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TWiP 41 Letters

Adam writes:

What up Doc's?

I'm writing to voice my complete disagreement with the sentiments of Sven Urban, in his letter on TWIP 38, that you as hosts are prone to engage in a ‘degree of banter which is distracting'.

I'm sure Dickson does not mind being antagonised, and like caffeine on an adenosine receptor the antagonist in this case is a vital educational aide serving to keep me awake.

I will concede the point that Dr. Racaniello is most often the instigator of these disruptions. For negative control please see the first episode of TWiV which Alan and Rich did on their own - this ran disappointingly efficiently, depriving me of company and edu-tainment on the latter half of a long commute to uni.

I will end with this observation - If you can't play as a child you can't be imaginative, and the last thing we need is scientists without imagination (I believe these are called accountants btw).

You have this listener's permission to be as disruptive as you like.

Keep up the good work.


Melbourne, Australia (26◦C Partly Cloudy)

PS: Consider this my vote against This Week in Old Guys Reading Aloud from Textbooks (TWiOGRAFT).

Liesbeth writes:

Hi Vince, hi Dick,

my name is Liesbeth and I'm doing my Masters in Epidemiology of Infectious Diseases at the Oswaldo Cruz Institute in Rio de Janeiro. I started to follow TWIV a couple weeks ago and now I'm absolutely infected with TWIP and trying to catch up with TWIM also. Thank you so much for this great initiative, for the effort and time dedicated... it's really appreciated and highly contagious! Keep up with the amazing podcasts!

All the best,

Bill writes:

Dear TWIP Team

30-40 years ago, completely unaware of giardia, when hiking in the high Sierra we commonly drank from mountain streams without any ill effect. There's much greater awareness since then, but I wonder if the risk of infection has really increased. i.e. if drinking from fast flowing streams at high elevations is as safe now as then. What do you think?

Arthur writes:

Vincent Racaniello and Dick Despommier- you guys are GREAT!

I discovered TWiP one month ago and so far I'm addicted, I don't know how many guys in Kenya listen to TWiP, I suspect I'm the only one but I'm quickly spreading the gospel. I have special interest in the Leishmania podcast because I came across so many patients with Kala Azar especially during my internship year in Eldoret- Kenya, last year and I have seen firsthand the kind of clinical havoc the parasite can cause. A few questions;

Q.1 Why do patients with Kala Azar have pancytopaenia (most of the time-severe)?

Q.2 Apart from the BMA and the Splenic Aspirate, what are the rapid diagnostic methods that are available and how accurate are they?

The doctors working for MSF- (doctors without borders) in Pokot (an area near the border of Kenya and Uganda where Visceral Leishmaniasis is endemic) usually base there diagnosis on epidemiology and some rapid testing methods and start treatment- mainly sodium stybogluconate but some patients still die, so over to my next

Q.3 How effective is Sodium Stybogluconate in the treatment of Kala Azar? Is Amphotericin B more effective despite its side effects?

Observations: In Kenya the most vulnerable age group are kids around the age of 6 years because they play on and around anthills where most sandflies are found.

Prof. Despommier and Prof. Racaniello, it would be really great if you give lectures in Kenya- the medical fraternity here will really appreciate it.

Dr. Arthur Mumelo - Medical Officer - rural Kenya.

Roxanne writes:

I am a new to the podcast. I gotta say I love the repartee. I find it entertaining and it sometimes adds suspense when the answers are put off for a bit. As a disclaimer: I am an avid CarTalk fan. Your names, Vincent and Dickson, even share an alliteration component like Click and Clack.

Roxanne, PhD (microbiologist turned forensic DNA analyst, public health hopeful)

Daniel writes:

In the early TWiP episodes Dr. Despommier spoke at length about neurocysticercosis. You mentioned that the neurocysticercoses remain dormant and the patient is asymptomatic (unless they obstruct the foramen magnum) until they begin to die and subsequently cease to suppress immune response. My question is, if cestodes that become neurocysticercoses have no aging genes what causes them to die? Is it because they are encysted and can't gather nutrients from their environment?


Ethan writes:

I had some questions regarding the difficulties in producing successful vaccinations for sleeping sickness. From my understanding, the biggest trouble is that as the immune system produces effective antibodies and the trypanosome populations decline in the host, gene expression for molecules making up the outer VSG coats in progeny switch to quiet genes thus changing the VSG molecules and rendering the host's current antibodies useless.

Why can't we vaccinate against all of these antigen variations? If that is impractical, why can't we vaccinate against every 10th antigen, for instance, so that once the trypanosomes turn on one of those genes it is then eliminated by the host's inoculated immune system? I'm also curious as to whether the trypanosomes always begin their life in their host with the same VSG or if it will vary its first expressed gene. If it always starts in the same place and uses a specific order, we could better select which ones to make vaccines for.

Since the trypanosomes switch these genes in a specific order, can we catalog this progression in a model and use that as a reference for the host's current and future antigens? If so, we could select the most relevant vaccine that would be effective against the impending wave of new antigens, playing the waiting game for our target gene to be switched on.

Sorry for the barrage of questions, this just had me thinking the last few days. It seems to me a vaccine for this should be easy - but obviously I'm wrong!

Christopher writes:

Hello gentlemen,

First off I want to thank you both for an excellent and entertaining podcast. I am a regular listener and I enjoy your show immensely!

I had a question regarding the "successful systems attract parasites" quote. Dr Despommier mentioned that this quote had won a poll in which readers were asked to vote for the pithiest statement on biological research over a specific time frame (or perhaps that best summarized 100 years of biological research??). As part of an upcoming faculty lecture series, I am preparing a talk on how- at least from an ecological perspective- that statement is perhaps better worded this way: "parasites play key roles in defining and structuring successful systems". Unfortunately I have been unable to find any reference to this poll online, and I was hoping Dr Despommier would be so kind as to remind me of the details (what publication / organization ran the poll, what were the "rules" of the contest).

Thanks for your time, and I look forward to more awesome podcasts in the future!

Cheers, Chris
Christopher Blanar, Ph.D.
Assistant Professor of Biology
Division of Math, Science, and Technology
Farquhar College of Arts and Sciences
Nova Southeastern University

Stephen writes:

Re: using sari cloth to filter water to reduce cholera, the agent being filtered is a copepod that carries Vibrio, not the Vibrio itself:

"In laboratory experiments employing electron microscopy, we found that inexpensive sari cloth, folded four to eight times, provides a filter of [about] 20 [microns] mesh size, small enough to remove all zooplankton, most phytoplankton, and all V. cholerae attached to plankton and particulates [greater than] 20 [microns]."

Links to download a pdf of the PNAS paper:

Reduction of cholera in Bangladeshi villages by simple filtration

PS, I wrote to TWIV previously regarding hyperparasitoids. I really like the extended format and the fact that your shows feature people who know what they're talking about, or admit that they don't know.

Chris writes:

Hi Vincent and Dickson,

Love all your podcasts. I just wanted to write in to clarify a couple of things that were said on a couple of recent TWiP episodes.

On TWiP 37, you were discussing the use of water filtration in the eradication efforts of dracunculiasis and the subject of the work of Rita Colwell came up in which she used sari filtration to filter out Vibrio cholerae from natural water sources. Dickson mentioned that this might be possible due to V. cholerae's long flagellum. In fact, the reason this is possible is because of V. cholerae's affinity for chitin. The majority of the bacteria in nature tend to be attached to small crustacean zooplankton. It is this property that allows enough of the bacteria to be filtered out of the water to significantly reduce the incidence of cholera in areas using this practice. Thus, because of this, I think it would be unlikely that this type of filtration would have a significant effect on removing other enteric bacteria (infectious dose playing a role here too).

On TWiP 38, you were discussing Babesia, and Dickson said that the species was bigemina. However, B. bigemina is vectored by Boophilus ticks and is the cause of a cattle disease known as 'Texas cattle fever' or 'red-water fever'. In the United States, Babesia microtiis the species that most commonly infects humans and is vectored by Ixodes scapularis ("deer tick") in the U.S. Northeast and New England regions. Thus, it is B. microti that is the most important species infecting humans and has a deer tick - rodent life cycle. Since it infects red blood cells, it has also been an issue for the blood supply.

Just wanted to clarify those two statements not as criticism, but more to get the correct information out there. Keep up the great work with the podcasts.

Chris Whitehouse, Ph.D.
Microbiologist working for the U.S. Government in the Washington, D.C. Area

Allan writes:

I've enjoyed listening to your your TWIP podcast. You are a wonderful story teller and though I have worked in this field a bit as well, I never fail to learn something. I listen in the car on Sticher. My kids think I'm weird but they like it too.

In the episode today (1MAR12) on dracunculosis, you made the natural connection that we come across cyclops both in Malaria and the Guinea Worm programs, but in the podcast you mentioned a couple times that mosquito larvae eat the cyclops and I think you probably meant the converse.

We add cyclops to family water jars in Cambodia to eat the mosquito larvae.

Anyway keep up the great work. You strike a nice balance of making the field more approachable, while keeping it interesting enough even for the grouches.

Best regards,

Allan, DIH, MPH

TWiP 40 Letters

David writes:

Love the TWIPs! I'm a helminth user (25 hookworm for allergies), so your programs are fascinating!

Dr. Racaniello, after listening to TWIP 33 where you were discussing the history of your surname, I thought I'd give your listeners a way to remember your obviously Italian name. It's the rap song, "Black and Yellow"! lol

Peter writes:

Dear Professors,

please do NOT abandon your style ever!!

Even if there´s some privacy in there, be it fishing or simply the weather or whatever, it has to be in your podcasts because it makes them authentic! Even more, talking like you with so much commitment and humor increases the amount of learning. You know why!

I always tried to be a good teacher (for natural sciences at a german secondary school since more than 20 years) exactly in that way.

And scientific researches in recent years have approved that the brain of all ages learns better and more effectively with these attributes.

Here you are:

And remember, just because informations cause an emotional response, and that means attention is rising: (page 7)

Please keep on with your excellent work, you are pioneers in science and "face-to-face" interaction,

greetings from Wiesbaden, Germany


Richard writes:

Dear Dickson & Vincent,

I recently delivered a lecture to nursing students at Kilimanjaro Christian Medical Centre in Tanzania, on a subject that Dickson is very well versed, Trichinella.

I am a medical entomologist & have no knowledge of Trichinella so quickly had to do some reading & piece together a basic lecture. In the process of preparing the lecture I was left with a couple of questions that I hope Dickson can answer.

1- In East Africa the species is Trichinella nelsoni. My understanding is that there have been very few human cases reported (200 ish) and they have all come from eating undercooked warthog or bushpig. In Tanzania pork meat from domestic pigs is commonly eaten (on a sidenote pork is called "kiti moto" in swahili which translates to "hot chair"- possibly because if the muslim population of Tanzania get caught secretly eating pork they will be in big trouble, or the "hot chair"). I was left wondering why T.nelsoni has not made the jump from wild pigs & warthogs into domestic pigs? I was asked this question in class & my explanation was that it could be due to geographic isolation as warthog/wildpigs are mainly found in "bush" and savannah areas where usually only Maasai are found. Maasai keep cattle, sheep, & goats but not pigs. Do you think this is a reasonable explanation? How would you have answered this question?

With rapid population growth in Tanzania do you think expanding human settlements could result in T.nelsoni making the jump into domestic pigs & resulting in more human cases?

2- In the excellent book, "Manson's Tropical Diseases" the T. nativa Arctic cycle shows that polar bears can become infected by eating raw walrus and seal meat. How do seals & walrus become infected with Trichinella? Don't they eat fish??

Looking forward to hearing your thoughts.

Best wishes


Ethan writes:

Hello Vincent & Dickson!

I'd like to thank you for the superb podcasts I've had the pleasure of enjoying the past few months. Not having any previous interest in parasitism or virology, I downloaded a few podcasts on a whim and was immediately hooked!

Working a night shift by myself in the biology building of a university calls for TWIx podcasts for entertainment. While listening to the TWIP episode on hookworm, I noticed a ton of slides left out in a lab room full of microscopes. What was on them? Parasites galore! I took the liberty of finding slides of hookworm in various stages of life cycles and got to follow along during the podcast and actually see with my own eyes real examples of what you guys were describing under the microscope - it was awesome!

I really enjoy being able to learn from TWIP being a non-scientist (although I'm going back to school for physics soon, so I'll be in the scientist club before too long!). I have to look things up to follow along in TWIV, and TWIM is often way over my head, but I try to listen to both anyway, they're always interesting.

I've since listened to all the TWIPs and would love to hear new ones added more often. I'm also looking forward to adding Dickson's new book West Nile Story right beside my recently read copy of Parasite Rex.

Sorry for the lengthiness of the email!

Thanks again,


Rebecca writes:

Hello again!

Thanks for mentioning my email and talking about my obscure profession! Cytotechs screen pap smears in addition to fine needle aspirations from just about any body site. A normal day consists mainly of screening pap smears, but I get to look at some lung, thyroid, liver cells, etc. Legally, we have to screen all paps at an appropriately licensed lab with a Medical Director and Technical supervisor. Gone are the days of screening in your underwear at home - well, maybe some folks can still screen in their underwear. My workplace frowns on it. A lot of slides are still hand screened on an regular ol' light microscope, but some are analyzed by a computer first. All slides must be screened by a cytotech or pathologist - the computer just uses an proprietary algorithm to determine the areas of the slide with the highest probability of abnormal cells to guide our screening. We send all slides we diagnose as abnormal to a Pathologist. He or she has the final say. In addition to looking for cancerous or precancerous cells, we also look for non-cancerous infectious agents. HSV and CMV produce some gorgeous cells! Check google images for HSV or CMV cytology. As far as it being kind of boring to just look through the scope all day: you have do enjoy looking through the microscope or you will quickly go insane in this line of work. I personally enjoy the focused attention this work requires - it's like mediation for me. Bonus: I get to listen to awesome podcasts while helping people. Additionally, the microscope rarely back-sasses me, so I don't have to deal with any workplace conflict or stress:) Thanks again for the podcast!

Dan writes:

Hello gentlemen,

My name is Dan and I'm considering becoming an epidemiologist. I discovered your podcast and am slowly working my way through all of the old episodes, which I find extremely fascinating.

Forgive me if it's already been mentioned on your show as I am listening to the episodes in chronological order and haven't yet arrived at the most recent one, but I would like to recommend a book called "Parasites: Tales of Humanity's Most Unwelcome Guests" by Rosemary Drisdelle. I recently purchased this novel and it served as a wonderful primer for your show and as fantastic "thought food".

If you can recommend any books, journals, or other publications that would be helpful for a budding young student such as myself I'd be very appreciative. I know for certain that with my next paycheck I'll be buying Mr. Despommier's "Parasitic Diseases".

Thank you very much for publishing this podcast! I'm very happy that I've discovered it.

Best regards,

TWiP 39 Letters

Rebecca writes:

Thanks for the podcast! I wanted to add a quick note about diagnosing trich: As a cytotechnologist, I diagnose trich on pap smears daily. I imagine this is how a lot of ladies find out they are infected.

Peter writes:

Greetings Dickson and Vincent,

A cool overcast 14°C on the Eastern Mediterranean coast of Turkey as I write this.

Further to my question on a previous TWiP about whether parasites that used blood feeding vectors made the host more attractive to the vector I found this article on parasitic manipulation in vector-borne diseases

and this 2005 study which indicates that malarial parasites do manipulate their mosquito vector's biting behaviour:

The results look positive even if the number of test subjects was very small.

It was a slow day at work so I had time to spend on the internet.
A couple of other interesting items I found:

A new genus and species of leech (Tyrannobdella rex) from Perú that feeds from the mucous membranes of animals and when feeding may remain in situ for several days.

Blood feeding by proxy - the East African jumping spider Evarcha culicivora feeds on vertebrate blood by preferentially preying on blood-fed Anopheles mosquitoes. Not a parasite, but still interesting.

I would also like to suggest a possible guest for TWiP - Dr James Logan of the London School of Hygiene and Tropical Medicine

Cam writes:
I'm an amateur at this, looking for some help with identification.

These are in human blood, drawn at night via pin prick to the finger, magnified about 300x. No additives or stains. Nocturnal periodicity, so not found by any more conventional method. Note the thin, translucent folds on the head shot, and "V" shaped head. I was thinking mansonella, but the egg and nocturnal periodicity are not right for mansonella. M. perstans has a ribbon-y quality at the tail, not mid-body.

Warm regards,

p.s. Also wondering what the object is at 3:00 on the tail shot.

Peter writes:

A POTENTIALLY lethal tick infection newly identified in Australia has mysteriously emerged on the NSW south coast.

Doctors have revealed the first reported Australian case of human babesiosis, a tick-borne infection that carries a 5 to 10 per cent
fatality rate, higher than the death rate from the most common tick bite infections.

The victim was a 56-year-old man from the south coast who died, it is thought, partly as a result of babesiosis. In a report published today in the Medical Journal of Australia , doctors say the infection probably contributed to his death from
multi-organ failure last April.

The report of the first babesiosis case in Australia thought to have been locally acquired had raised ''intriguing questions'' about how
the infection is spread in Australia, the lead author of the report, Sanjaya Senanayake, of the Australian National University, said.

Todd writes:

I was reading news from my childhood home, Louisiana, and saw an article about a surge of heartworm infection due to a warmer and
wetter than normal winter (more mosquitoes roughly translates to more heartworm infection). The more concerning statement though: "...even more disturbing is that some dogs, who have been on a heartworm preventative medication, are still coming down with the potentially fatal disease."

Can you offer some details and insights into what the vets are seeing?|mostview

Peter writes:

Hi TWiP Team

I was talking to someone about animal diseases and they sent me these links to some plush parasites:

Francois writes:

Hello Monsieur Despommier & signore Racaniello,

Before all, sorry for my English.

And It's now 24°C in southern France. First water restrictions of the year.

My research years were oriented toward food safety & ferments selection. A.k.a fight Listeria in food with other bacterias or cheese ecology.

During, this previous life, I've found some some pretty amazing cheese ferments.
And I'm quite sure the smell & taste of some the resulting raw milk cheeses would have killed mosquitoes & parasites alike.

I've recently listen the oldest TWIV & TWIP, with exceptional pleasure.

I would like to follow on Mr Despommier comment about the 1981 movie "Quest for fire" (TWIP 10), & his suggestion that parasites exchanges between modern & Neanderthal humans could have been deletarian for Neanderthal.

Now, with proof that those populations have reached a certain level of intimacy, at least in the case of the Denisovans. What kind of traces paleoparasitologists could find to conclude that this was indeed hapenning : traces on bones, eggs or cysts in caves soils.
Or at the, now available, genetic makers. Ex : drepanocytosis ?

There was also wooly mammoth, sabberthoot tigers & bears in the film.  Do people get parasites by eating elephants, bears or big cats meat, because it seems that the megafauna was a frequent part of the neandertal diet and vice versa ? I've also heard about tiger, bear or canid meat in today asia, & seen hippopotamus meat in Togo.

Other info, I was 7 in 1982, when I & most of my school mates saw the film. No one have been bothered by the most "X-rate" part, but we were freaked by the "eat people alive bits by bits" part. Today the film is frequently seen in school by children between 7 to 10 years old.

Best regards, & all my thanks for those amazing efforts.

PS : For Mr Despommier
La Tour vivante (The Living Tower)

TWiP 38 Letters

Carlos writes:

Dear Vincent Racaniello and Dickson Despommier

I am an avid listener of TWIP since its start, have been following TWIV for at least two years and, surprise, also follow TWIM.

My field is Computer Science, but I crave for information in all areas I find interesting. To me, your Podcasts fill the role of giving me very pleasurable conversations on science, and help me better understand fields where nature dictates the validation of the research. In my field we often deal with the construction of artifacts that are validated by their mathematical properties, so the validation process is a bit more detached from nature.

What prompted me to write now is that I just listened to the start of TWIP #33 and your discussion of how google scholar indexes more publications and citations, than PubMed I believe, but with a more messy presentation format. You might find it useful to explore a new tool that allows authors to aggregate papers in a specific google scholar author page. After one does that, its easy to sort by publication year, impact etc.

Take a look at the following link to see how to set it up:

The strong point is that the tool makes it very easy to identify (and separate) your own publications and co-authors. For more common author names its often a mess to separate one's articles from the other homonymous authors.

Keep doing the excellent job of promotting interest in your fields and science in general.



Universidade do Minho,

Peter writes:

Just watching a clip on cellular metabolism. The background music was the Vangelis theme from Carl Sagan's Cosmos.
A very great sadness came over me.
He looked outward whilst you guys look inward, so to speak.
I feel sure he would have loved your shows and would eagerly have embraced podcasting.
You are doing the inner Cosmos.
Thank you.

Emerson writes:

Hi guys,
love the show.

You listed csf, blood, lymph, urine, aqueous humor, cochlear fluid, and semen.

I'd like to suggest that there are more than 7. Ignoring interstitial fluid and cytosol I'm fairly sure that bile is sterile before it leaves the gall bladder. Synovial fluid within the joints is typically sterile, the falopian tubes/ ovaries are bathed in sterile fluid. Tears are also sterile before they are cried I believe.

Take care!

Laura writes:

Drs. Vincent Racaniello and Dickenson Despommier,

I'm a Masters student doing research on Soil Microbes, and in my research have come across papers referencing Mollicutes (phytoplasmas, mycoplasmas, ureaplasmas, and spiroplasmas are examples). Are there any parasitic mollicutes that actively infect humans and cause detrimental symptoms?

Thank you,
Chatham University

Peter writes:

Taking the image challenge on the NEJM site i guessed wrong on a lung
sputum sample. Desperately trying to recall lung involvement parasite.

Ascaris? Bzzzzzzzt!

Of course not, dummy. Too quick on the mouse.

It was a bloody egg in the lung, not a juvenile organism, and I don't
think Ascaris does the disgusting stomach to lung thing?

Turned out to be paragonimus. -> Paragonimiasis

I don't recall that one in twip

Sounds interesting,

coming soon?

Ignore last email

D'oh! I realize you guys did touch on paragonimus. TWiP 27: Trematodes
Must have some in my brain.

Anyway, here's the link.

Brian writes:

Docs R & D,
At the end of your A. lumbricoides program you discussed problems related to Toxocara canis & T. cati infection in humans, namely VLM & OLM. Dick said it would be great if someone surveyed dog runs in NYC, or nearby, for Toxocara eggs. Sampling & counting eggs sounded relatively straightforward, piece of cake was mentioned a couple times. Such a survey would be an excellent topic for an enterprising high school student, with some help from a famous parasitologist or virologist, or someone they may know. Give it some thought.

I am reading Dick's book pick a while back, "The Fever" by Shah and find it fascinating. As an anthropologist, I am well acquainted with the sickle trait balanced polymorphism, but under-appreciated the impact malaria had on human history. The rapid spread of the parasite in the US hit home after reading how fast it infected areas of New England after the environment was altered by the building of mill ponds. It took only a few returning soldiers from the Civil War to infect whole towns. Incredible.

My wife took a parasitology class a few years ago and had to draw many of the specimens you have discussed. She thought Giardia trophozoites were "cute" with their little faces. After going though a Giardia infection, I'll tell you how cute they are.

As much as I love TWiP, I am happy with the longer break between episodes so I have time for the many other terrific podcasts like TWiV, TWiM, Science Friday Video (a favorite, if you haven't seen it), NYTs The Minimalist, Science Now, Nature, Archeology Channel, RadioLab, among others. So many podcasts, so little time.

And, I have to know how you selected the fun but creepy opening music and great hard-driving riffs at the close of the show. Good stuff.


Trudy writes:

Listening to you right now on Science 360 Radio. You mentioned this post and I had to comment. As a former nurse epidemiologist who worked in County Public Health Practice, I am a strong proponent for vaccination. I worked a number of vaccine preventable disease outbreaks including rubeola (measles) which resulted in individuals becoming needlessly seriously ill. Very much enjoy TWIV and TWIP and TWIM....My mother was also a nurse who worked in public health before most vaccines were available. She saw the tragic cases of diseases which resulted in great morbidity and mortality. I could go on and on about the good vaccines do. Thank you Professor Racaniello. Kudos to you and all who assist in the productions of your wonderful podcasts. Dr. Despommier is a treat. I have so many interesting experiences with all kinds of reportable diseases and conditions including on how I became a nurse instead of a medical illustrator or possibly a physician. I sustained a needle stick pre recombinant HBV vaccine while working my way through college in a teaching hospital. I carry natural immunity to hepatitis B now. Didn't get extra credit in my micro class, however.

Best regards,

retired from public health but never tired of pathogens and learning about them...
Naples, Florida

Ricardo writes:

Hello Vincent and Dickson.

I just came from my first jury in a monographic work where the student cited TWIP. The monograph title was "Trichinosis: from the parasite to the ecosystem".

I was very impressed with the "watermark" left by TWIP on the student, and happy that my friend (her supervisor) suggested her to listen to TWIP.

One of my colleagues from the jury commented the text looked like a romance. She appreciated the "stories". :)

Thank you both for the really great work you are doing.

Ricardo Magalhaes, Ph.D.

Associate Professor of Microbiology
Faculty of Health Sciences of Fernando Pessoa University

Felix writes:

Hi Professors,

In episode 16 on Giardia you discuss Antonie van Leeuwenhoek and his early adventures with a microscope. Here are a couple of interesting resources which discuss him:

Firstly an article in the ASM magazine claiming that Leeuwenhoek gets too much credit for his discoveries, some of which should be shared by Robert Hooke of the Royal Society of London.

Secondly, an excellent BBC documentary "The Cell", which begins with Hooke and Leeuwenhoek.

You have also mentioned Paul De Kruif's book "The Microbe Hunters" as one of the few sources for information on the history of germ theory and microbiology. A recently published book (also from the ASM) addresses the same area, most likely with a less idiosyncratic style than the dated De Kruif volume:

Germ Theory: Medical Pioneers in Infectious Diseases
Robert P. Gaynes
ISBN: 978-1555815295

Just while writing this email I discovered the ASM book store with a section of the history of science
(I have no connection with the ASM!)

I am currently re-listening to all of your TWIP podcasts, having listened to them all at least twice when they were first released. They're are just that good!

I really love the beginner-level approachability of the first 30 or so episodes.
It would be great if you could cover a small number of highly important non-parasitic diseases, such as cholera, in the same style.

best wishes,

Jim writes:


I'd really like to hear the details of your efforts to convert Dickson's text to electronic format for access over the web. Lessons learned should be useful to anyone with similar thoughts. How is it different from creating such a work from raw materials? I'd prefer it as part of the TWIP's, if that is acceptable.


I'm still hear all the TWIM, TWIP and TWIV's, but my podcast listening load is heavy (60/wk) and production of a weekly blog about the best entries is slow for an old-timer.

Loved Dickson's link to the stop-action high-speed photos of the liquid drops.

Smithfield, VA

Sven-Urban writes:

Dear Profs Racaniello and Despommier,

As a long time listener of TWiP (and for that matter TWiV and TWiM) I feel obliged as well as entitled to express some - mild - criticism that I feel and hope is appropriate.

While Your mutual friendship is a much valued aspect of the show, I think it might lead You to a degree of bantering that interferes with the contents. Slightly too often I find Your discussion interrupted by mutual jibes, which make me lose the thread of thought. I would say that generally, though not exclusively, Dr Racaniello is the instigator of these interruptions. I am, of course, not now referring to those abundant, seriously intended and equally seriously phrased questions that Dr Racaniello interjects, but rather about occasional stray comments and jibes that appear in private between very close friends. I think the term "in private" here is crucial, as I doubt that You would express Yourselves like this were the two of You jointly presenting before a class.

Today I could, by the way, compare TWiP #37 ("Dracunculiasis") with TWiV #172 ("Two can be as bad as one", with Kathy Spindler) - both in a one-on-one setting - and the difference in tone is remarkable.

Naturally I speak here only for myself, of course, but I for one would appreciate if You might henceforth tone down the sparring, keeping in mind that You do actually appear before a large, international audience, not all of whom might appreciate or be able to follow Your bantering. (And just to be precise, "tone down" does not necessarily mean "discard".)

This notwithstanding I am very grateful for the set of podcasts You so graciously provide us all with!

Sincerely and Respectfully, Yours

Robin writes:

This from

- plural noun 1. Often, Acta. official records, as of acts, deeds, proceedings, transactions, or the like

< L, neut. pl. of āctus, ptp. of agere to do; cf. act

Robin writes;

The TWIP podcasts again emphasize to me the difference between hearing first-hand from someone with experience in contrast to hearing material regurgitated by someone with book-knowledge. It made a world of difference listening to a trauma surgeon or an emergency physician from a trauma center speak in contrast to similar material presented by someone without direct experience.

Sarah writes:

Greetings Dickson and Vincent!

I am a new listener and I am thoroughly enjoying working my way through the TWiP and TWiM podcasts. I found your conversation regarding Draculunculiasis very informative. I think it is great that you spent a good portion of time emphasizing the necessity for clean water for overall public health. It is something that we often take for granted here in the U.S. Something caught my attention though. You talked about the use of cheap cloth to filter water in the prevention of Guinea worm and mentioned that it was unfortunate that this wouldn't prevent diarrheal diseases. I attended a session at the ASM general meeting a few years ago to the contrary. While Sari cloth won't prevent viral borne diseases, it does seem to reduce the incidence of Cholera. Here's the link to the study which was published in the first issue of mBio:

Kind Regards,

Assistant Professor of Biology
Gordon College
Barnesville, Ga

Ian writes:

Dear Drs. Twipaniello and Twipommier,
On the topic of the Dracunculus life cycle: Is there evidence that a male is required for fertilization? Some nematodes are parthenogenic and "virgin birth" for this worm would be a nice compliment to the biblical story of the cadueceus (sp??).
Keep up the good work,

Alicia writes:

I`ve heard that Toxoplasma gondii might be caught by touching a leech. What`s the general consensus on this?

Thanks and keep up the great work.

TWiP 37 Letters

Cam writes:

Dick Despommier is often talking about the importance of ecology when understanding parasitism. Does he have any suggestions for good introductory texts to the subject for someone of my lowly level?

I recently came across this article, which led me to the idea of Oogst. Has Professor Despommier come across this, and how does he view it in relation to the idea of Vertical Farming?

Raihan writes:

Hello Guys,

Sorry but I wanna share a non-parasite related news story with you guys.
Came across this article about how the government in Singapore is deciding to invest in roof-top gardens here, as a measure of controlling the recent cases of flash flooding here.

When I read it, i was reminded of Dr Despommier's brain child, the Vertical Farm. I guess this is not exactly a farm but it has a lot in common and displays another way of how incorporating fauna in cities can help solve problems in an urban setting.

You guys may choose to read this email on your Vertical Farming Podcast instead of TWIP.

That should be coming pretty soon right? *cheeky grin.

Love the show

Matt writes:

Dear Dickson and Vincent,

(Not sure if I sent this to the right place on the microbe world website, but as I noticed that you gave this email address at the end of the podcasts I thought I'd try it as well...)

Thanks for your wonderful series of podcasts; I have been working my way through all of TWIP and you are currently keeping me sane whilst I data-enter several thousand clinical records from a malaria prevalence survey. I also have TWIV on CDs which I listen to in my car on my commute route to my workplace in Muheza, North East Tanzania. And I'm very excited by TWIM which I will indulge in soon.

I am a medical entomologist currently working on insecticide-treated materials against malaria vectors and have a question which I hope you'll discuss on TWIP in relation to malaria but also in a broader context. It is this: do you think we already have enough tools to control (many) infectious diseases and that funding should be channeled into improved application/delivery of those tools and away from the search for novel techniques and 'blue sky' research? For malaria, we already have a diverse arsenal of proven weapons and auxiliary tools including bed nets, indoor residual spraying, intermittent preventative treatment, house screening, rapid diagnostic tests; GPS and mobile phone systems have vastly improved surveillance, we have subsidized and highly effective frontline drugs for treatment, amazing repellents and lures for mosquitoes etc. etc. People like Fred Soper and Malcolm Watson were incredibly successful at reducing malaria 60+ years ago with a much more limited arsenal. You might say that there was much less resistance to insecticides and anti-malarial drugs in those days, but in recent times two brilliant weapons emerged that are still being used, to which there was no resistance, i.e. pyrethroid insecticides and artemisin-based combination therapy (ACTs). What do you think are the major stumbling blocks in infectious disease control? Is the health sector too slow to act on research findings*?

Many thanks and keep up the good work.

Matt, National Institute for Medical Research, Tanzania & London School of Hygiene and Tropical Medicine

p.s. I wrote this before I saw the topic of Twip 35! I hope this question is still relevant (and I'm going to listen to that episode now once I can download it!)

p.p.s. I thought you might like to know that my two dogs are named after you! (Vincent and Dickson - jpg)

Dr Matthew J Kirby
Fieldsite Project Manager PRISM
Amani Research Centre
National Institute for Medical Research

Heather writes:

Dear Doctors R&D,

I love your podcast! It is wonderful to listen to commuting to work and while I am working as the support technician for the chemistry and microbiology teaching labs at our small state college. My favorite thing about your show is that the format is similar to the "seminar" or "journal club" courses that were my favorite in graduate school (that was back when I too wanted to be a "dr.", before I became a lapsed microscope jockey. Maybe I will go back to grad school....maybe...some day). Basically these 1-2 credit courses consisted of grad students getting together with a professor to pick apart papers in specific disciplines such as microbiology (we went over the "old" "elegant" research that was the foundation of modern microbiology), microbial genetics (we called that one "cloning club), current topics in molecular biology, current topics in elasmobranch biology, and current topics in shellfish aquaculture. My background is in fish and shellfish pathology, specifically the microbial and parasitic (and molecular aspects thereof) diseases of cultured fish and shellfish. Bearing that in mind, while I realize that you focus your podcasts on human/public health issues related to parasitism, might you consider doing an episode about epizootic parasites (or microbes or viruses) that impact humans economically and/or ecologically? Some examples that come to mind are my good friends QPX (quahog parasite unknown) or Perkinsus marinus in the New England shellfishery, "bumper car" disease in Long Island Sound lobsters, or the recent controversy surrounding the ISAV (infectious salmon anemia virus) outbreak in the Pacific Northwest. Then of course there are always parasites that are just fun for their "gross" factor like "salmon poisoning disease". Regardless if your decision regarding the discussion of parasitism of non-human animals I will continue to look forward to your TwiP, TwiV, and TwiM podcasts.

Thank you!


P.S. I read "Parasite Rex" as a freshman in college and it is still one of my favorite books!

P.P.S. "Monsters Inside Me" sometimes grosses me out, and that is saying a lot for it's accuracy!

TWiP 36 Letters

Trudy writes:

Dear Drs. Despommier and Racaniello,

I am almost caught up listening to TWiP! I look forward to your future efforts and eBooks, etc., however, in TWiP # 32, I thought I heard you mention that there would be a link to Dr. Despommier's lectures. I couldn't wait to go to your website and check them out. Unfortunately, the link was missing. You know what they say about the missing link, don't you? It must be a cryptid! But seriously, hope you will post the link to the lectures at your next opportunity. Please? :-)

I am dreading listening to # 33 because there are no more TWiPs available yet. I live in a semi tropical climate in SW Florida so tropical diseases and parasites are especially interesting. The only good thing about being current with your series, is that I can start to catch up on TWiVs and TWiMs. I did find Dr. Racaniello's lectures in Virology on iTunes and am watching this series. I started with the hepatitis Delta virus. It is of special interest to me as are all forms of viral hepatitis.

Dr. Despommier, please consider doing a podcast on vertical farming and even throw in some other tidbits of gardening wisdom.

I took the user survey as you request. Perhaps the results will help you in your future efforts. The way you two work together on TWiP makes for a delightful experience. Science, medicine and pathogens "float my boat" so it is a great pleasure to have two learned professors so engaged in interesting discussions.

I have written before. Hope this isn't too much. Consider that you are talking (via my earbuds) straight into my noggin: I feel like I know you both and it is an honor.

Best regards,

Peter writes:

Brian writes:

Vincent & Dickson,

My wife pointed me to TWIP and what a blast. My 23 year old son and I are making our way through the early episodes during our commute to and from work and loving every minute of it. After listening to the tapeworm episodes I will NEVER pet a dog from Wyoming or any other of the sheep states.

I'm not sure if you have covered the evolution of parasites, we're only up to episode 9, but that must be as crazy as ever. Surely you have enough material for several years worth of podcasts, but I'd like to hear a bit about how an animal accumulates such a bizarre life history.


Peter writes:

Dear TWiP team.

I was speculating about parasites that modify host behaviour and a possible strategy that may have evolved in those transmitted by blood feeding vectors.

To achieve optimum transmission of the parasite uninfected blood feeding insect vectors should find infected hosts more attractive than uninfected ones and once the insect vector had itself become infected its behaviour should change so that it would then preferentially seek uninfected hosts.

Has any research been done to determine whether any parasites that employ blood feeding vectors actually do modify host smell and vector preference in this manner?

As I was writing I was thinking of arthropod vectors such as mosquitoes and biting flies but it occurred to me that there are other possible blood feeding vectors such as vampire bats and leaches whose behaviour could also be potentially modified in this way.
Are there any zoonotic infections that are transmitted by leach vectors?

Lastly, I have seen blood feeders described as Hematophagous and Sanguivorous are these synonymous, and if not what is the correct/preferred term?


Gopal writes:

Hello, Vincent & Dick,

This month's issue of The Scientist has this interesting article:

Can't help wondering, somewhat uneasily, what our own parasites make us do!



Don writes:

In your discussion of Wolbachia in filariasis, Vincent suggested tetracycline for therapy. Dickson opined that it was too toxic and expensive . Au contraire, in the QID form it is "dirt cheap" and has been used widely since the mid 50's. Prolonged use does cause mottling of the teeth, and florescence of the bones under Woods light, not a problem for most of us. Wonderful Podcast, and deeply appreciated. Thanks

Kyle writes:

Top O' The Mornin' To Ya! (I'm not Irish - I just like the phrase..)

I would like to thank you for putting together such an excellent podcast. I'm currently a Med Tech working in a parasitology laboratory and enjoy my days searching through blood and pooh for those tiny life forms that you describe so well. I was introduced to the world of parasites by a course I took as an undergrad. The course instructor was one Dr. James B. Jensen. Judging from your earlier talks, I trust that this name will sound familiar. As you can imagine, the course taught by such a well known parasitologist was an amazing experience. I have a great passion for parasitology, and I'll see what kind of future I can put together. Thanks again for the great shows. I encourage you to continue, and add my voice to those that are calling for more. It is This WEEK in parasitism, you know! :)


Jim writes:

Vincent and Dick,

Delighted to hear the latest TWIP on the malaria vaccine. You guys mentioned using impregnated bed nets to reduce malaria. The NY Times had an article at:

This article described using poisoned bait to reduce the mosquito populations by a bunch like 90%. Would love to hear your thoughts on this.

Was also delighted to hear you guys are going to have more TWIP.

Am still devoted to TWIP, M, V.
Thanks much and 73

Kelly writes:

Hi, Vincent and Dickson.

I'm a PhD student at the University of California Davis and a long-time listener of This Week in Parasitism and This Week in Virology. I have a great appreciation for the fact that you two are successful scientists who take time out of your busy schedules to share your love of parasites and viruses with the general public. In fact, I was so inspired by This Week in Parasitism that I have since begun podcasting about science topics myself! Thanks for the inspiration!

I thought you two might be interested in an "experiment" in science crowdfunding called the SciFund Challenge. One exciting aspect of this experiment is that we're exploring a potential new source of funding (i.e., the general public) for small science projects at a time when everyone seems to be complaining about how difficult it is to get grant money. While this aspect of the experiment is certainly exciting, the most exciting part to me is the fact that crowdfunding forces scientists to engage with the public. Not only does the public get a chance to learn about cutting edge research, but they get the opportunity to have a voice in deciding the direction of future research through the money they donate.

While I think you might be interested in learning about a program incentivizing scientist engagement with the public, my motives are not entirely altruistic. I have a SciFund project focusing on how trematode parasites manipulate the behavior of their hosts, and I'm wondering if you would be willing to help me get exposure to my RocketHub proposal for this project (URL is here:, or go to and search "Support Zombie Research"). I study Euhaplorchis californiensis (EUHA), a trematode parasite infecting the brains of California killifish. EUHA manipulates the neurochemistry and behavior of their fish hosts, a fact which I find endlessly fascinating. These parasites have essentially had millions of years to figure out how the fish's brain works, and to figure out how to manipulate brain chemistry to achieve their own goals. I'm working on quantifying the extent to which the parasites modify the behavior of their host, and am trying to figure out the mechanism by which these parasites achieve their extraordinary behavioral manipulation. I believe parasites have a lot to tell us about how brain chemistry influences behavior, and I think of my research as an exercise in coercing EUHA to tell me what it has learned over millions of years about brains and behavior.

If you would be willing to tweet about my project or mention it in any other way, I would be endlessly appreciative. I'm happy to answer any questions you might have about my study system, as it's pretty much my favorite thing in the world to discuss!

Trudy writes:

Dear Drs. Racaniello and Despommier,

I just discovered your wonderful Podcasts! I am a registered nurse who has an unusual background. I worked as a diener at a teaching hospital while working my way through college. My mom was an RN also when there were few vaccines. She graduated in 1935. She would often discuss what she had seen as a public health and Army nurse anesthestist in WWII. She had a library of medical textbooks that I enjoyed reading . I spent part of my career as a nurse epidemiologist (county public health practice) and as an STD clinician, where I got to work with all kinds of infectious diseases and conditions (viral, bacterial and of course parasitic.)

I have been interested in infectious diseases and conditions since I was a young child when I got my first microscope. Also I have been lucky enough to live in semi tropical Florida for over 30 years. The University of S. Florida still has a great series of podcasts from their medical school's Division of Infectious Diseases. They also discuss tropical medicine and have a College of Public Health.

My first in person experience with a parasite specimen which really "hooked" me on microbiology was that of a tapeworm which was in a huge (tall) container in the foyer of Abbott Labs in Chicago. I was with a group of High School students which had a NSF grant in collaboration with Northwestern University's College of Medicine.

I have been fortunate to see a lot of interesting things because I also did some bio-medical illustrations. I am both an artist and a nurse.

To make a long winded email shorter...Your podcasts are infectious...I believe there is no cure or treatment other than continuing as a listener to you discuss microbes in your most engaging fashion.

Thank you for sharing your knowledge and experiences!

Trudy in Naples, Florida

Paul writes:

Hi guys

Just discovered the podcast.
Listening to 2 shows a day ...working my way up.....absolutely love dr. House ..parasite rex....and monsters inside me:)
While gathering information about parasites i often see these so called zappers little devices that kill parasites ..what are your thoughts on these.....and the history of using electric devices in killing parasites.

Greetings from switzerland

Josh writes:

Dear Drs. Despommier and Racaniello,

I am an auditor. To occupy my mind while I work I started scouring iTunes for science rich content. I saw your show "TWIP" and thought why not? I think the first TWIP I listened to was #33. I was immediately hooked. I went home and subscribed to TWIP, TWIM, and TWIV that night.

Currently I am listening to all of the TWIPs in a row before I start the other shows. I love the education, the ick factor is pretty high but this show provides me with an EXCELLENT free education, and helps me confront fears that were boogey men in my mind by giving me real quantifiable behaviors and characteristics of many things I have had uninformed fears about ( i.e. Trichinella, Toxoplasmosis, and tapeworms).

I am very saddened that I didn't know who Dr. Despommier was prior to November of this year. In the Spring of 2011 I was writing a business plan for my entrepreneurship class and I advocated that my group do our project on vertical farming. We were unable to find any resource that would provide us with information on how to successfully integrate a vertical farming business into an urban area such as Phoenix AZ, where our fictitious business had to be. We had thought about potentially buying a tall structure like an empty condo tower, or office building and converting it into a farm, or placing farms on roof tops (kind of like they do in Cuba). Sadly we couldn't find any cost to benefit analysis, yield per acre data, or potential profit margins with which to build our fictitious business plan. We ended up using another idea of mine, recycled building material sales. I remain sad that we were unable to write a plan for vertical farming.

Thank you for providing me with such a wealth of free information. Thank you for presenting it in such a content rich way, without spoon feeding the listener. Please continue to do these shows. I am indifferent to frequency as long as I can continue to have access to your knowledge and experiences.


Rachel writes:

Dear Dr. Racaniello and Dr. Despommier,

I'm in the process of choosing a career (PhD or MD)

I would love to follow in your footsteps and become a professor, researching parasites and leading the young minds to new discoveries! However, when talking with my parasitology teacher it seemed like he was discouraging me due to the lack funding and interest in the subject. I wanted to know your opinion, especially Dr. Despommier's. Do you think part of your success in your area of research came from the 'newness' of the subject or is there still an opening for hopeful parasitologists.

Thanks for all the work you both put in to the TWI series, I am a huge fan.

I am waiting anxiously for the next installment of TWIP.

TWiP 35 Letters

Trudy writes:

The more I listen to your fantastic podcasts, the more I love them. wO0t. I am the Naples, Fl nurse/artist who has written before.

Because I did get the pleasure of tracking reportable diseases and conditions in Florida, I was struck to know that other states did not require reporting of giardiasis.
Thought you might find the link to the list in my state interesting.

I do have a question...if you answered it can you mention the podcast number, please? It is more of a TWIM question, but I would like both of your comments because of the urban gardening interest by Dr. D. When tomatoes were suspected of being the source of a widespread salmonella outbreak in the not too distant past, there was speculation that the organism was contained within the tomatoes' cells!!! I garden, was a biology art major before finishing my BSN. This made absolutely no sense considering the differences between animal and plant cell structure. Also, what does Dr. D. think of organic gardening?

You also may find it interesting that Florida does allow land application of bio solids after processing in a wastewater treatment plant. Considering some of the encysted pathogens, I always felt this was unwise. Not every County allows it.

All the best from your very loyal long learner with ear buds which are rapidly embedding as a result of your "infectious podcasts"...


Dang, you are the best, guys. Listening to the podcast about crypto right now.

Gave you 5 stars and wrote a "glowing review" (ala Mark Crislip) on iTunes.

Alexander writes:

Dear Drs. Despommier and Racaniello,

I've really enjoyed listening to your podcast and learning about all of the fascinating parasitic diseases that they don't teach us enough about in medical school. I'm a student at Boston University School of Medicine but currently taking a year off to do HIV research in Uganda. Among other things, I'm hoping to perform a retrospective study looking at the impact (if any) of soil-transmitted helminth infection on antiretroviral treatment outcomes in a cohort of HIV-infected individuals in rural Uganda.

At any rate, my real question for you has to do with treatment of schistosomiasis. I happened to be swimming in Lake Victoria last weekend (self-preservation is not one of my strong points...) and am thinking it may not be a bad idea to take some PZQ. My question is: how long does one need to wait after potential exposure to schisto for PZQ to be effective? My favorite new textbook, Parasitic Diseases 4th Edition by Despommier et al (have you heard of it?) says that PZQ is effective against the adult organism. However, it sounds like it takes several days for schistosomulae to migrate from the infection site to the liver, only then at which time they develop into adults. Provided that schistosomulae are also susceptible to PZQ and the drug has good subcutaneous tissue penetration, it should be fine to prophylax even within the first days after exposure. However, if this is not the case it may be necessary to wait some period of time to ensure that any schistosomulae have had time to transform into adult worms before administering PZQ. Any thoughts on this?

Finally, I just wanted to say thanks for taking the time to create and sustain TWIP. It's always a pleasure to listen in, and I'm actually finding the information you provide in the podcast (coupled with your wonderful textbook) to be quite clinically relevant here in Uganda.

Thanks, and all the best,

PS - here's an idea for a future TWIP episode: a review of clinically relevant (or otherwise interesting) interactions between parasitic infections and other infections, e.g. genital schisto increases susceptibility to HIV infection in women. I think one important and possibly under-emphasized point by Peter Hotez and others at the forefront of advocacy around NTDs is that it is valuable to target NTDs not only for the purpose of eliminating these infections themselves but also for mitigating any pathogenic synergy they might have with other more "sexy" diseases like HIV.

Cedric writes:

Dear Vincent and Dickson,

I recently read this paper discussing the phenomenon of self medication in animals. The authors speculate that this behavior was selected for, at least in part, due to the antiparasite properties of many of the plants, animals, or materials consumed by animals for reasons other than nutrition. I was wondering if Dickson had any more information on this process, and what his opinions are regarding the origin of self medication in regard to parasites.

Thanks so much for all of your work in developing TWiV, TWiP, and TWiM. Your discussions have given me a real head start in my undergraduate biology classes, and I look forward to every episode.


Ricardo writes:

Novel Drug Wipes out Deadliest Malaria Parasite Through Starvation

Theodore writes:

Good day (or night),

Starting from October I've listened to about half of the TWIVs, all the TWIMs and the TWIPs. I find them to be very enjoyable, the semi-Socratic method of teaching is quite refreshing. However, two particular subjects have been underplayed.

First Toxoplasma. The papers by Fekadu, Lindova and McAllister are great primers for the studies regarding the behavioural effects of T. gondii. The Gaskell one is by far the most interesting though. So, hands down, the leading theory for schizophrenia's etiology is an inappropriate level of L-dopa, the precursor for such molecules as dopamine and epinephrine. Depending on the population studied, seroprevalence of T. gondii induced IgGs among patients with schizophrenia is as high as 97.7%. Though there is some ambiguity as certain studies report a 42% seroprevalence amongst schizophrenics, compared to 11% in controls. Regardless of the exact rate, it has a statistically significant presence in schizophrenics and people with other mental health problems.

Just a correlation though. A tongue in cheek refute of correlative studies is the stork theory (will be paraphrased/butchered). The idea is that from 1970-1985 there was a surge in the German birth rate. At the same time, there was a surge in the stork population of Germany. Their coincidence was statistically significant. Of course, we know this is bupkis. Storks and babies aren't actually related. However, if we found that there was a drop in condom sales, we could have an aha moment, due primarily to the fact that we can name the mechanism for why that correlation actually matters.

Back to Gaskell, and the aha mechanism for toxo and schizophrenia. Their group shows that T. gondii has two fully functional enzymes specific for producing L-dopa, and they show that these genes are transcribed specifically when the parasite infects neural tissues, and that the enzymes produced do make L-dopa. We really can't prove that toxo causes schizophrenia with Koch's postulate since putting a brain parasite into a volunteer isn't all that nice. However, I'm flummoxed to think of anything else that is needed to point at T. gondii as the causative agent for some types of schizophrenia.

Ricardo writes:

Global warming wilts malaria

TWiP 34 Letters

Raihan writes:

Hello Professors Racaniello and Despommier,

In TWIP #33, Dr Despommier said that certain parasites do not need receptors to enter cells, while Dr Racaniello then said that all viruses require a receptor for entry. I might be wrong but don't certain paramyxoviruses like Respiratory Syncytial Viruses enter the host cell by mere membrane fusion? I hope I'm not missing the point here, but i remember being taught in my undergraduate course that there are a certain class of viruses that don't need a receptor at all.


Steve writes:

I first read of the Red Queen's Hypothesis in Parasite Rex by Carl Zimmer, which list Dr. Despommier in the acknowledgements. Recently there was an story in The Wall Street Journal: "Why Sex? To Keep Parasites at Bay, of Course" by Matt Ridley. I believe it would be very helpful to hear your thoughts on the Red Queen's Hypothesis.

Thanks, we appreciate all of your great podcasts.

Scott writes:

Vincent & Dickson,

I listened with great interest this afternoon to the TWIP story on malaria vaccine (via Science360 - I am not an academic, but a true science junkie). My keen interest is due to the fact that I lived in Nigeria for some time and suffered from P. falciparum infection seven times before I was finally able to build enough immunity to not suffer mightily. No cerebral, thank goodness! But it left me with a passion for watching developments in the study of the parasite and the science of malaria control.

In listening to the part on the TWIP podcast about the locus of injection site being critical to efficacy for this possible vaccine candidate, a thought occurred to me: Since mosquitos are so adept at finding blood vessels from which to suck their bloodmeal, why not create a genetically modified mosquito that would produce the candidate vaccine protein in its saliva, so that when it inserts its proboscis into the blood capillary, the host gets a tiny injection of the protein at the same time. While I do expect that not a single mosquito bite would produce immunity, of course, the many thousands that one receives over time, might do the job, and would maintain it over time, as "booster shots" would be received daily. Since this vaccine seems to be efficacious against all the strains it has been tried against, it would suggest that the parasite's docking protein is highly conserved in evolution, making the evolution of resistance much less likely.

If the same genetic sequence were also used to invoke immunity to Plasmodium by the mosquito itself, it would give the mosquitos an evolutionary advantage in the environment, in that there is also a cost to the mosquito as well in carrying the parasite. This would ensure that the genetic modification would become dominant in the mosquito population over time. It would also provide a double-pronged attack on the parasite - both at the mosquito and human blood stages of the parasite's life cycle would be suppressed.

While I recognize that there are surely some formidable barriers in the way of creating such a system and deploying it in the field, my thought is that it might have enough promise to be worth looking into.

Warmest regards from (so far) malaria-free Cartago, Costa Rica,

Trudy writes:

Listening to you in Podcast #6 on tapeworms. You are making me laugh. I live in Florida. Not everyone is retired in Florida. Not even people who live in South Florida are all retired.
FYI Whole Foods does list the country of origin of the animal proteins sold in their stores.
With my background in Public Health epidemiology and communicable disease clinic (STD clinician...TB outreach), I have never seen a tapeworm in a specimen since moving to Florida. I had seen on in the teaching hospital I worked at in Grand Rapids, Michigan in a specimen from an immigrant. Now I said not everyone in Florida is retired and they are not...but I am retired (early).

Cattle ranches are not just in the panhandle either...many of these ranches are all over the state. Florida is a big state, we have a lot of open land used for all types of agricultural purposes. While there are beef cattle grown in Florida, many more farms/ranches are devoted to dairy production.

I am a nurse, an artist and a Florida Master, microbiology and infectious diseases continue to be of tremendous interest to me.

Charlotte writes:

In TWIP 33 you asked which protozoa should be discusesed in future episodes. If you discuss Acanthamoeba as a "Trojan Horse" you can correct errors made on two episodes of TWIM regarding Legionella as endosymbionts of Acanthamoeba.

I think listeners would find comparisons of Acanthamoeba, Neglaria and Hartmonella (in terms of pathogenesis and as bacterial reservoirs) interesting.

Thank you for the podcasts, without which I would never sleep.


P.S. The "Trojan Horse" term was coined by Barker & Brown, but everybody uses it now.

TWiP 33 Letters

Howie writes:


Great podcast!!!

A while ago, Dick made a comment along the lines that Sir Ronald Ross was a dim bulb. Ross did much more than "just" discover that bird malaria is transmitted by mosquitos. He was a closet mathematicians and published about 20 papers and books on pure mathematics (see

He was also a superb infectious disease transmission modeler.

Germ theory was developed in the 1850s. Before then, people believed that diseases such as cholera were caused by a miasma, a noxious form of bad air. About 60 years latter, Ronald Ross, a public health physician, developed two ODE (ordinary differential equation) transmission models for malaria [Ross, 1910] that made the following predictions:

Germ theory was developed in the 1850s. Before then, people believed that diseases such as cholera were caused by a miasma, a noxious form of bad air. About 60 years latter, Ronald Ross, a public health physician, developed two ODE (ordinary differential equation) transmission models for malaria [Ross, 1910] that made the following predictions:

1: One does not need to kill all the mosquitos in an area to prevent malaria epidemics. There is a threshold value of vector capacity,  below which the disease quickly dies out in humans. This conclusion was at first rejected by the experts, but proved correct by field trials in Malaysia where malaria transmission essentially ceased after draining the mosquito larval habitats.

2: Malaria can not be eradicated by treating humans alone. Even if the number of infected humans is reduced by 99%, if the mosquito population remains unchanged, then the disease prevalence will rebound to its former value.

3: The endemic level of infections is lower for longer lasting infections, e.g., it is lower for P. vivax than for P. faciparum infections.

Of course, mathematical models can not prove anything, but they generated novel hypotheses which were found to be correct and saved countless lives.

Ross was also the first to present a mechanistic model of the transmission of a generic infectious disease.

Not bad for a dim bulb!

Please, never stop TWIVing.


Professor of Mathematics

Georgia Institute of Technology

Spencer writes:

Dear TWIP,

I really enjoyed your analysis of the Malaria Vaccine article from the New England Journal of Medicine.    You guys had an interesting discussion about the different phases of clinical trials and I thought it was incumbent upon me to clarify these phases.  As a clinical investigator, I oversee several Phase 1 clinical trials.  A Phase 1 trial is a dose escalation trial:  It is simply carried out to assess safety at various potential clinical doses of a compound.  Obviously, before a compound makes it to such a trial, there has been some demonstration of effectiveness in animal models, or some reasonable suspicion that the compound will be a useful treatment for the disease.  Phase 1 studies are small - typically 20-80 people and it is in this phase that side effects can first be seen.  A Phase 2 trial targets the maximum tolerated safe dose in a specific population that either has the disease or is at risk for the disease.    There are usually 100-300 people in a Phase 2 tri al.  In addition to looking at continued safety at the studied dose, the compound in question is studied for its effectiveness in treating the condition or disease in this phase.  In Phase 3, the compound is compared to standard of care treatment, often in a head-to-head blinded fashion.  In some cases, there is no defined standard of care treatment.  Alternatively, in some cases, such as you discussed about HIV, it would be unethical to withhold conventional treatment while evaluating the new compound.  This makes Phase 3 trials very difficult to complete.  Also, Phase 3 trials usually require thousands of participants and take a long time.  Phase 4 trials are post-marketing trials.  The compound has already been approved for sale and prescription by the Food and Drug Administration.  Many of the side effects and sometimes disasters associated with some medications are not apparent until the drug is taken by 10s of thousands of people after it is already released.  I hope this is helpful to listeners and I just want to remind you guys that there are still some interesting parasitic lifecycles and histories to discuss for which we are still waiting.  Keep up the great work.

Jim writes:

I was jolted to hear the casual mention in TWIP 28 by Dr Gwadz of chiggers and scrub typhus.  I thought chiggers were one of the local pests I could ignore other than itching during routine encounters with them each summer.  This summer at the worst point I had over 50 on two legs despite deet all over my shoes, socks and lower pant legs.  One or perhaps two adjacent bites produced a large blister in contrast with the usual small, red, itchy nodules.  No other symptoms, but now I'll be alert associated symptoms.  During scrub typhus research with Google I saw instructions for soldiers about tucking trousers into the tops of their boots as a protective measure.  I assume this is the reason for "blousing boots" done by the Army, but don't recall ever hearing that was the reason.

Another great TWIP, by the way.  A small group discussion seems to produce the most interesting results.

Thanks again.


Smithfield, VA

Michael writes:

I love TWiP!

I am starting my parasitology class (for a Medical Lab program) this fall. I am also excited to be able to learn and understand many more of the details now that I have the basics down because of TWiP.

I also have enjoyed being able to use all of the TWi_ podcasts to form questions for my friend in Physician Assistant school who then often asks her classmates the same questions (I bring up topics you say are not often taught in medical schools and the unusual cases, and put them into a type of case study, adding the most vague hints as she and they get stumped). Due to your podcasts I will be able to better grasp everything I learn and be able to help impart critical thinking skills to other health care professionals.

Also, Do I remember hearing that a 6th ed may be coming out of the Parasitic Diseases book? I would love to add that to my studies! If so, any idea when? Did you say it may be avaliable on ibooks? I also encourage you to consider Kindle, for it is easier to read the text on a Kindle, and anyone with a computer, ipad, iphone, android, ect. Can get the free Kindle app and read it and view any color pictures.

I would still like a higher frequency, but so long as you just don't stop, I will be happy with whatever you can do!

Anything associated with Infectious Diseases and how humans interact with and are affected by them is my passion!

Thank you for giving me chopped and dried wood to put onto the fire!


Jim writes: (incomparable TWiP 30)

Just incomparable!  Pure knowledge; so much expertise in one place; another podcast in my Best Podcasts folder.  All the TWIV, TWIP and TWIM podcasts are great, but they are readily accessed, too, so far, and I'm capturing a collection of less easily retrieved audio files for times when I can pass on the collection to interested folks which has already occurred twice.  A couple TWIP's are there to capture attention and alert listeners to where similar files are available.  I'm sure your backup plan is excellent, Vince, but I'll happily store copies of everything, if you need another remote site.


Smithfield, VA

Alan writes:

What creature/parasite/worm can I catch from eating a cockroach snack late at night?

I can't decide which entertainment personality I like more, Vince or Des Pom. Its not just the subject its you guys that I listen to.

Have fun,


P.S. I am with Dixon on the orchids.

Scott writes:

Hi guys!

This article popped up on a facebook feed I subscribe to; probably you already are familiar with the material, but just in case I thought I would pass it along. I have an interest, but no expertise, in tropical medicine, and would like to hear your opinions.

Ricardo writes:

Alex writes:

Hello Doctor Racaniello and Despommier,

Curious if you might have some incites on a particular malaria life cycle. I've been reading on Plasmodium vivax.  We know that Plasmodium vivax can relapse via the hidden agents stored in the liver, termed 'hypnozoites'. But time and time again through multiple sources it's stated that vivax malaria relapses much more quickly in patients in tropical regions over non-tropical regions, on the magnitude of several months.  For the life of me I cannot explain this, the parasite would seemingly detect the same body temperature and conditions within the host regardless of where they are living. I have two theories here; Perhaps the hosts are indeed different, with varied levels of nutrition and other factors causing the hypnozoites to convert earlier in tropical cases and later in better nourished non-tropical cases. Or, on the other hand, the cases of "relapses" could be muddled by actual cases of re-infection. Since you are more likely to get an infection in a tropical region the relapse rates seem lower in non-tropical regions. Any thoughts?

In TWIP#31, Doctor Despommier mentioned that a man by the name of 'Macgregor' conducted a statistical analysis to determine the number of cases needed to maintain malaria infection within the population?  I was unable to find this paper, and curious if you might be able to link in within the show-notes next time.  I'm extremely interested to see these figures. It seems to me that we might be on the cusp of a medical paradigm, with a vaccine that's 50% effective it may be the extra push with the combination of mechanical preventative strategies (bed nets, ect.) needed to eradicate the disease.  Is there such a thing as 'vector-based herd immunity'?  Conventionally, 85% of individuals within a population must be immune to maintain herd immunity within the entire population.  I know this is complicated by the fact that it must be essentially eradicated within two populations (humans and mosquitoes), and therefore likely to result in a much higher threshold of immunity.

Keep up the great work!

Todd writes:

I'm reading this article and take a small issue with item #5 :

The first part of this paragraph makes perfect sense:

If it's parasites or other risks associated with sushi that worry you more than mercury, Andy Bellatti suggests you put your mind at ease. "Fish served in sushi restaurants has been previously flash frozen, which kills parasites as effectively as cooking," he explains.

Particularly confusing to me though, and if memory serves, contrary to a comment that Dick made about farmed fish (though I think it was in reference to a sheep borne parasite (liver fluke maybe?)) is the second part of the paragraph:

[Andy] also points to Steven Shaw's book Asian Dining Rules: Essential Eating Strategies for Eating Out at Japanese, Chinese, Southeast Asian, Korean, and Indian Restaurants, which explains that most fish used for sushi in restaurants around the world are farmed to avoid the problems with parasites in wild fish. "Fish like tuna are not particularly susceptible to parasites because they dwell in very deep and cold waters. Sushi restaurants typically use farmed salmon to avoid the parasite problems wild salmon have," he explains. The fish that are at times likely to have parasites, like cod or other whitefish, aren't used for sushi anyway and are generally served fully cooked.

I suspect it is more about which parasite they're referring to than the absolute of "all parasites."  Can you clear up my confusion?

Keep up the great work guys!  TWIP and TWIV are both part of my commute routine.  It makes me wish my drive was longer...well...maybe not...but your penchant for educating the masses is earning you karma points daily!


P.S. Ronald Jenkees *ROCKS*!  You should hear his unreleased music, which he has linked from his website.

Luca writes:

Dear Vincent and Dick,

Once again I write to you after listening to TWIP episode 32, where Vincent went off on a tangent to discover the meaning of acta in the various scientific journals.

Here I am to shine some light upon it. As an Italian, I learned that word in primary school, when we were taught that every day, in Ancient Rome, all that had been discussed and decided in the Senate would be put up on a poster in the Forum, the public square, so that the people could know about it. This was called Acta Diurna (loosely, record of the day) - of course there's a wikipedia page for it: Here it is! It goes into much more detail than I ever would be able to. I probably got it wrong in some details, too. Primary school was long time ago.

Once again thanks for your constant, excellent work in education and public outreach, I have now expanded my weekly podcast schedule to include TwiM, but I have to admit that TWiP is still my favourite.

All the best


PS: here's an added bonus - I knew the meaning of Despommiers, but was curious about Racaniello, so looked it up online - there's no meaning as far as I can tell, although to me it sounds like some kind of edible root in Italian. However, I found the Racaniello coat of arm, in the corresponding wikipedia page - - did you know about it? And you have a (rather mean) family motto, too: Dominus exquisitus artis saeviter quis revocas malum memet (I possess a refined art, that to hurt cruelly whoever does me evil). Cheery-o!

TWiP 32 Letters

Raihan writes:

Hi Guys,

I saw this video during the course of listening to TWiP. Is there any parasitic truth behind this phenomenon?

Amazing Podcast. You guys are revolutionizing education.


from @Sophie on Twitter:

Please do a TWiP on Baylisascaris procyonis

Jim writes:

TWIP 26 on the schistosomes was equally interesting. I did some serious thinking about a swimming episode done in Cam Rahn Bay, Vietnam in 1971, but never had any problems, yet. I heard that shistosomes either stopped or prevented invasion of Quemoy and Matsu Islands by the Chinese by wading across an isthmus probably in the early 1900's. Neat analogy with Schwarzenegger.

Smithfield, VA

Suzanne writes:

I think most wild salmon are caught at sea. Would any parasites they picked up as youth in rivers stick with them then?

I've been told that from an economic/environmental point of view Alaska does a very good job fishing (and not overfishing) for wild salmon. That's one reason I buy Alaskan wild salmon. I don't think I'll stop, but most of what I buy is canned and cooked. Or smoked. I do like salmon sushi occasionally, though... hmmmmmm.

Chad writes:

I came across an organism named Naegleria fowleri while I was going off on tangents from a wikipedia search.
This looks like an interesting organism for your podcast, (assuming it is considered a parasite.)

Thank you,

Jim writes:

Prof Despommier:

In your excellent TWIV 22 about hookworms you noted that after the Civil War lethargy was a major problem in the South due to hookworm infection. My local newspaper today contained a long article about difficulties US troops have in training and working with Afghan troops, stating in part that "...American forces often characterized their Afghan counterparts as drug abusers and thieves who were also incompetent, corrupt and lazy with 'repulsive hygiene.'" Do you know of parasites in that part of the world which could lead to a person being seen as incompetent and lazy, especially if they have poor hygiene, or if studies have been made to identify prominent parasites in Afghanistan or that region? No other details about these characteristics were offered in the article, so we don't know, for example, if the repulsive hygiene description is by necessity, due to cultural differences, or laziness.


Smithfield, VA

Alberto writes:

Dear Vince and Dickson

Following the release of TWiP #27 (Trematodes) I attended grand rounds at our hospital where an interesting case was presented that was coincidentally relevant to this recent episode.

A middle aged man presented at our hospital with severe liver dysfunction and was eventually found to have a Fasciola hepatica infection (a single egg was seen in a stool sample). The CT and NMR scans clearly showed tracks of necrotic tissue in the liver but the most impressive graphic was a video of the gall bladder ultrasound where multiple flukes could be seen moving in and out of the field of view of the scanner.

The presenting infectious disease registrar believes the source of infection was fresh watercress consumed with a traditional Lebanese dish of raw beef (Kebbeh nayyeh). The watercress was obtained from the patient's friend in Forster on the Northen New South Wales coast, in sheep country.

Apparently there have been other cases of F. hepatica infection including one in Melbourne associated with cultivated watercress.

I am still catching-up on old episodes of both TWip and TWiV. I look forward to hearing more about molecular hydrogen generation by parasites. Is anybody looking at cloning the enzymes involved in this pathway for commercial exploitation.

Keep up the amazing effort guys.
Molecular Haematology Lab, Institute of Haematology
Royal Prince Alfred Hospital

Ryan writes:

Just so you know...

I could listen to Bob tell stories all day long! Great episode, guys!

Ryan Rogers
Texas Parks and Wildlife Department
Possum Kingdom Hatchery

Jim writes:

Professor Despommier,

I realize both you and Dr Racaniello are concerned about public health issues, but this seemed at first glance to be of greater interest to a parasitologist than a virologist. However, please don't prevent Vince from commenting. So, may I get your comments about this Thirstaid Bag from Britain ( Despite its small size it looks like another possible item for my emergency equipment box for use in a local disaster, or for travel anywhere water quality is questionable. It's compact, tough and lightweight and has a filter shelf life of 5 years. Of course some iodine pills or small bottle of clorox would be much cheaper, so is it a cost effective item? I wonder, also, how temperature affects the filter and also how a user in the field could test the water it produces to verify filter effectiveness. For example it could be on the shelf for 4.5 years and have just produced some 200 or 300 liters of water out of its 350 maximum. The manufacturer says the filters are stamped with a production date and once placed in use are effective for a year, or I presume, the 350 liters. Let's say the bag and a 3oz bottle of clorox are stored in a car glove box or car trunk in Florida for 2 years and then in Massachusetts for 2 years, before a need for them occurs. Do you think both will be as effective as when produced?


Smithfield, VA

James writes:

Dear Vincent and Dickson,

I have finally caught up with all the TWIP podcasts! In October, I will start a position as an assistant professor in host-pathogen interactions at the Faculty of Veterinary Medicine at the University of Calgary. My background is in biochemistry and bioinformatics. I completed a PhD at the University of Edinburgh on genomics of parasitic nematodes and a postdoc in Toxoplasma gondii at the Hospital for Sick Children in Toronto. In my new position, I hope to return to nematodes - if the funders will permit me!

Although my work is focused on genomics, I readily see the importance of classical parasitology, e.g. taxonomy and systematics, cell biology and ecology. In recent podcasts, Dickson has referred to the end of the golden age of parasitology and the closure of parasitology departments. Rest assured that there are still groups of Young Turks telling anyone who will listen and shouting at those who won't about the importance of all aspects of parasitology, not just DNA-sequencing.

I want to thank you both for your efforts in TWIP - I continue to learn a lot, especially the history and social aspects. With respect to the basic biology, I am continually blown away by the invasion and survival mechanisms of these parasitic critters. Trying to understand them better is what gets me out of bed in the morning, that and a cup of tea!

Listening to Robert Gwadz was inspirational and I look forward to hearing from other legends in the field.

best wishes


Faculty of Veterinary Medicine,
University of Calgary

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