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TWiP 57 letters

Anne writes:

I found TWIP just a week ago and feel I've found a home. I'm a pharmacist, usually on the night shift, and stay excited all night listening to you. Parasites have always been my hobby. In fact, I recently divorced one. His life cycle is unique. I get oddly thrilled when dispensing anti-parasitic drugs. Thought I was odd. Thanks for normalizing me. Annie

Renato writes:

Hello dear TWIP hosts!

Just in case you are not already exposed to this, I send you the web address for a recently launched worm-watching game:

It consists of video feeds of C. Elegans, which are being recorded automatically by tracking microscopes. As far as I understand it, the researchers want to measure the efficacy of the serotonin-regulated musculature of egg-laying for each worm, so recording when the eggs are layed is a vital piece of information.

This game is from the same guys that spawned Galaxy Zoo, where you classify galaxies, and Planet Four, where you classify terrain formations in Mars. Actually they have several interesting "scientific games", so I'd like to pick their project menu for this week:

Also, there is something I'd like to ask Dixon. In TWIP 56 you and Vincent had a brief discussion about the name TWIP, why it uses the word "Parasitism" instead of "Parasitology". It has occurred to me sometimes that the "P" in a "TWIP" show name could also mean "Pathology". Whenever I think that, I wonder if all parasitism is a pathology - not necessarily a human pathology, but some living being's pathology. I then usually imagine that Dixon could argue that not all parasites cause harm to their hosts, and therefore parasitism is not completely within the scope of pathology. Is that the case?

Thank you and all your guests for the shows!


Oops, terribly sorry for misspelling your name, Dickson!

(I guess I always think of the Dixon from the "Mason & Dixon" line when I hear your name. By the way, the book by that name by Thomas Pynchon is an awesome read (well, all Pynchon books great, but M&D is arguably the best one so far)).

Chris writes:

On your last TWiP someone mentioned the Pandemic Board Game. I stumbled upon a YouTube video of it being played and explained by Wil Wheaton (the actor who started out as a teenager on Star Trek, and now shows up on various television programs):

Apparently the person who starts is someone who had recently been sick, or had the worst disease. It turned out three of the players had caught H1N1 in 2009 at a gaming type convention in Seattle (link so you can understand what they mean by "Pax": ), but one of them had suffered worse a few years before with a sequences of strep infections.

Enjoy. Just like I enjoyed learning about parasites in fish due to transporting them elsewhere.


(And I really hope that my two college age kids going to that same gaming convention don't get some kind of infection!)

Garren writes:

Hi all

I have a short bit of trivia to add to TWIP #56. You briefly discussed the topic of fish spawning and the salinity or not of the water in which the fish spawn. The question of a salty river was oh so very briefly brought up and dismissed. Well there does in fact exist a salt water river. I have been there and it is on the Island of Okinawa. The river is spring fed and the spring is so close to the ocean that the ocean water actually infiltrates the spring and it flows its extremely short length back to the ocean. It is something like 1-2km long. I have a picture burred around here somewhere but I know not where at the moment.


Robin writes:

Joe writes:

Vince and Dickson,

Here is a follow up on your biofuels question. To make fuels from crops succeed we need a biotech breakthrough that I really thought someone would have done already. Basically we need a bug that eats cellulose and converts it back to sugar so you can ferment it. Personally, I think there is a Nobel Prize in it for the group that creates an e. coli strain that converts cellulose to sugars. Once you have that, then you can feed the farm animals the corn and run your tractor on the corn stalks! Or you could use hay or grass clips or wood chips or waste paper, whatever is available cheaply. Until we get that bug, ethanol from corn will just be a niche technology.

People will keep pushing to use corn crops or other high sugar crops to make fuel, but the economics are not good and the lost opportunity costs are too high. Look how the modest current efforts in the USA have pushed up food prices and still required government subsidies to be competitive. No doubt there is a listener out there with lots of arguments for how great ethanol from corn is but I don't see anything like the margin needed to make it a viable market changing crude oil substitute.

I will show my age and tell you that as a senior chemical engineering design project in 1980 at Purdue, we looked at how to convert crop waste materials (like corn stalks) into fuel and it wasn't pretty. The only real way to break down the cellulose was to grind it up and treat it with hot fuming sulfuric acid in big reactors. Fuming sulfuric is 98% concentrated acid that is saturated with sulfur trioxide gas, brute force chemistry for sure! As I remember, you could get pretty good conversion of the cellulose, but the ugly part was separating the good stuff from all the waste acid and the non reactive lignin. Once you got all the acid out of the good stuff, then you still had to ferment the sugars. It is not surprising that you don't see anybody running this process to make fuel! We need a biotech solution to break down the cellulose without all the mess. I think folks were looking at the microbes in termites' stomachs as a place to start., but I have not heard of any progress on this in several years.

I will add that biofuels are not the only option for our fuel supply. For the past 100 years, we have had repeated dramatic reports that we are about to run out of oil and yet it never seems to happen! I remember a particularly detailed one in Scientific American about 10-15 years ago with beautiful graphs and everything. Each time the trumpets of doom sound, some smart engineer or geologist comes up with a new way to extract more oil. I don't see any reason why this trend will suddenly stop this time, we still have lots of tar sands, deep oil, and shale oil that have not been touched. Please note that I am not expressing a political view on the social correctness of these options just the technical aspects. Even more impressive are the reported quantities of frozen methane hydrate clathrates on the ocean floor that would likely be fairly easy to extract. Some estimates are that there is more than 10 times the amount of energy stored there than in all the oil we have ever used. Obviously none of these fossil fuels address the CO2 generation concerns that many people have.

Wind, solar, hydro and even nuclear power all have their places and I hope their niches keep growing as the technology improves, but nothing comes close to competing with chemical energy as a cheap, portable, high density source of energy. One just needs to look at biology to see the truth of this; plants fix the suns energy into chemical forms that then cascade through the food chain ever evolving into more complex forms. How cool is that!

Thanks for helping me stretch my brain each week! Thus ends "This Week in Chemical Engineering"!

Warmest Regards,


Daniel writes:

Dear The Good Doctors!, I hope you are well!

I became fascinated with parasites at Uni when I was studying Freshwater and Marine Biology and took zoology and again relating to shifting global distributions of aquatic infectious organisms by climate change. I loved every aspect of parasitim but they were such small parts of my course I didn't think I could go into parasitology. I left college and went into aquaculture, listening to you all the while, which nudged me into returning to study. I'll be starting a masters in molecular parasitology at Glasgow Uni next year. I'm certain I wouldn't be, if not for you two and TWIP! I cannot express my gratitude in words for your effort and work making TWIP!

I love TWIP (et al.), I've been following it for years. However, I'm currently working at a remote pearl oyster farm in Australia (Beagle Bay, WA). As the podcast is over 50mb, my iPhone won't download it without a wifi connection. There is no wifi...

Is there anyway you can reduce the podcast file size? Without reducing the length of the show, of course!
File compression or something?

It's been months since I've had a TWIV fix and I'm starting to get the shakes!

Worm regards,

TWiP 56 letters

Suzanne writes:

Your discussion about technology and fixing things here before we go out into space made me wonder if space exploration might turn out to be like investigative science. In the process of exploring space we might run across the means of fixing our problems here.

Robin writes:

Ecology and parasites

Just as "weeds" are plants that seemingly have no use for us, but interfere with our attempts to cultivate plants in controlled ecosystems set up by us, parasites are organisms that interfere with the controlled ecosystems that constitute organisms, but seemingly have no use in the limited perspective of human timescales.

The parasites may have substantial functions in shaping natural ecosystems, such as in controlling population overgrowth, helping in modulating immune systems (as in preventing autoimmune bowel disease in humans with intestinal parasites, and in building herd immunity - which was lacking in New World humans to Old World viruses, causing New World human populations to be wiped out on contact with Old World humans) and quite possibly other influences as yet unrecognised.

Extermination of wolves - perceived in the same light as parasites - caused an overgrowth of herbivores, altering plant populations and affecting the ecology of streams and rivers.

Parasites can have effects on human social structures, as when the Black Death so reduced serf populations that they brought an end to the structures of mediaeval serfdom in Europe.

We have been around for 200,000 years, and have had an understanding of the organisms we call parasites for but a couple of centuries. Our attempts to reshape natural ecosystems to what we see as our advantage in our timeframes may have unintended consequences on evolutionary and geological timescales.

Parasites and hosts are in a dynamic dance within ecosystems, a dance that contributes to shaping the ecosystems over various timescales of which we see but a few frames, and even a small part within each of those frames.

This is so well exemplified in virology, where we have only recently come to recognise that our very existence now depends on ancient viruses that melded into our genomes.

Parasite ecology:

He also sent:

The Red Queen was Right

Blaine writes:

Hi there Twippies,

I saw this interesting link on the USDA website discussing the work of Eric Hoberg on the origins of tapeworms:

I would love to hear you guys interview Eric or have a podcast discussing the origins/evolution of some of these parasites. I find it remarkable to think about these complex lifecycles and how these parasites require two or more hosts to survive. It just doesn't seem like a great strategy for survival (other than the fact that it does seem to work). This leads to a lot of questions about how or where these things ever came from regarding tapeworms that use domesticated animals as part of their lifecycles.

One more question that you may or may not have hinted on in your podcasts. Do parasites have parasites (or commensals)? There must be bacteria and viruses that infect or live on parasites. Is anyone studying them. Can you comment on this too?


Fort McMurray, AB

John writes:

In TWiP 51 you speculated about the effect of wing muscle modifications on mating success in mosquitoes.

The subject of wingbeats and mating has been studied in the related family Chironomidae. Both families share an enlarged Johnston's organ
(hearing organ) in male antennae. Chironomidae are abundant and don't try to eat researchers, so they make better test subjects.

Males of most species form aerial mating swarms and listen for the wing beat frequency of females of the same species. I doubt females
listen for individual males, because they lack modified antennae. They may hear the swarm, and males could listen to each other to form into
a compact swarm.

A male of one of the larger lake-dwelling species might (metaphorically) say to a female:

"Meet me 5 meters over a contrasting dark object on the sandy beach at dusk when light has dropped below 50 lux. Beat your wings at 370 Hz
adjusted by 10 Hz per degree C of ambient air temperature above or below 20 C. I'll be waiting with a million of my friends."

The combination of swarm marker, altitude, and wing beat frequency is different for different species.


Ogawa and Sato. 1993. Relationship between male acoustic response and female wingbeat frequency in a chironomid midge, Chironomus
yoshimatsui (Diptera : Chironomidae). Medical entomology and zoology. 44(4):355-360.

To tie this back to parasitism, here is a picture I took of some ectoparasitic water mites on a midge (Chironomidae):

Joe writes:

Vince and Dick

As always I love your podcasts. You all made me laugh in TWIP episode 55 With Dick’s comment about the foreign nature of Chemical Engineers’ brains and Vince’s post modern nonsense about the evils of the internal combustion engine and denigrating it because it is was just so cheap.

Well let me take you on brief tour of how this Chem E’ brain sees the world.

The development of mechanical power to replace human and animal power is one of the single most important advances in human history. You may have heard of it, its called the Industrial Revolution. The rise of mechanical power is arguably the single biggest reason for the economic and moral decline of slavery as a viable social model on most of the planet. Slavery was rampant in the birthplace of democracy, ancient Greece, and not seen to be incompatible as it freed up the rich folks to have time to think deep thoughts. Mechanical power ranks right up there with the invention of writing, cities, mathematics and the scientific method as the most impactful events in our history that have enabled us to reach the incredible quality of life we have today. It has certainly had a much greater impact on the world than modern medicine or electronics both of which I value highly!.

The internal combustion engine in its various forms (2 stroke, 4 stroke, gas and diesel) is one of the single most successful inventions in history. It has beat out water power, steam power, coal fired boiler power or any other options in almost all applications with a few notable exceptions like centralized electricity generation. It is dependable, cheap, easy to repair, durable and scalable. This is the highest praise an engineer can give.

It has filled every available power generation niche in almost every conceivable human habitat and pushed its competitors to extinction. Here is a short list: weed whackers and leaf blowers, motorcycles, cars, buses, trucks, tractors, trains (diesel electric locomotives), ships, airplanes, portable generators, portable pumps and air compressors, One of the amazing things about the IC engine is that it has dominated applications where capital outlay is small with accompanying higher high operating costs (small engines) right on up to those larger applications where capital outlay is very high with relatively lower operating costs (locomotives, semi trucks and medium sized ships) Only at the very largest scales where turbine engines have an advantage do they lose out. Think E coli the size of an elephant for comparable biological example!

Imagine life in any large city without the IC engine. The quality of life drops dramatically. Public transit, food delivery, waste disposal, etc. all depend in the IC engine. I leave it to Dick to discuss the health and comfort impacts of all of us going back to horses. Don’t mind the flies and careful where you step!

Yes I know fuel cells and hybrids are so much cooler. Some day they may be one tenth as durable and successful as the IC engine. Some personal history will give some perspective, I started in a industrial R&D department in 1981 fresh out of college and I thought it was really great that about half of the R&D budget for this chemical company was going to developing membrane technology (AKA microporous separators) for use in electro chemical cells, which are essentially fuel cells running in reverse. We all saw the promise of the technology even then. They finally gave up years and many $$ later with little progress. The state of field has changed little since then and you can make the argument that this is a problem on the order of difficulty of our efforts to cure cancer. The devil is most certainly in the details. We engineers will keep working on these new technologies because that is how our brains are wired and there are some incredible advantages if we can ever make them work. But don’t disparage the IC engine until you can show me one of these new solutions going 200,000 miles over 10 years without several major rebuilds like so many old trucks and cars do ever day. Realize that the telling measure is that people only shocked when an IC engine breaks down much sooner.

If you stop and think about it, we all literally depend on IC engines on a daily basis in many ways. So the only real question is; “Have you hugged your engine today?”

All my best. You folks make my daily ride behind my IC engine a treat and are greatly appreciated!


PS. Yes machines are alive, just like viruses!

EH&S Manager

Amanda writes:

Hey guys!

Avid fan here, love all your podcasts, weather updates, and especially Dickson's digressions.

Just a teeny correction from TWiP #55. A listener (Jessie) picked the board game Pandemic. Unfortunately, you confused the board game with the flash internet game Pandemic 2. Minor, I know, but I don't want you, or any listeners, to miss out on the board game by thinking it's the same as the flash game. The two games, while equally awesome, are completely different.

In Pandemic 2 (The internet flash game and iPhone app) you build your pathogen and try to decimate the world through disease.

In the board game Pandemic, you work with 3 of your friends to eliminate 4 different diseases - developing cures and thwarting outbreaks. The game has a few levels of difficulty, and the expansion brings new elements like a mutated strain, a bioterrorist role, and even petri dishes to keep your game pieces in.

I highly recommend it! I was wary about the cooperative element, but it's a blast.

If I may, I'll submit the expansion as a listener pic: Pandemic: On The Brink
Also, for those that love Pandemic 2, there is an iPhone/iPad/iTouch app out there called Plague Inc that is very similar, but with a slightly nicer interface: Plague Inc

15 degrees Celsius and rainy here in Halifax, NS, Canada.


Post-Doctoral Fellow
Canadian Center for Vaccinology
IWK Health Centre
Halifax, NS

Judith writes:

My husband discovered TWIM for me. It was love at first podcast. I am retired after a wonderful and exciting 40+ year career in Public Health in San Luis Obispo, CA.

I have tried to keep up with Internet articles but your podcasts bring me back into the latest happenings in such an entertaining manner. Having gone through all the TWIM's I am now into the TWIP's. I love all of the regulars & am amazed at the collective depth of knowledge.
I have a strong background in evolution and ecology and love when you put the pathogens in their "places" in the big picture.
Mycology was my greatest love ... would enjoy a "TWIF"! Maybe you could clone yourself Vincent!

Question: Why TWI Parasitism rather than This Week in Parasitology for uniformity ?

I just found this article ... It is heartening that microbes are working hard to fix our messes.

Many thanks for all the hours of enlightenment! ... Judy

TWiP 55 letters

Jessie writes:

Hi Vince and Dick!

Has anyone volunteered to do transcripts for TWIP? I love this show, and I'd love to be able to contribute in some way. Forgive me if transcripts already exist and I'm just not finding them on the website. If no one is already working on this project, let me know and I would be happy to pitch in.

I am a nonscientist with a deep interest in biology, and the TWI shows are all definite favorites of mine. Thanks for making so much great content available.

P.S. - Have you ever played the boardgame Pandemic? As far as I know it's the only public health themed boardgame out there. It's challenging, and lots if fun. Call it a listener pick :);desktop_uri=%2Fwatch%3Fv%3DytK1zDPPDhw

Jessie in San Diego

Jenn writes:

First off, I want to say I recently discovered twiv and twip (and love them both). Thank you for such entertaining and informative podcasts.

Two questions:

1. Do you guys have any other shows?

2. I recently started going back to school, and started taking things I was actually interested in (namely biology). I had taken a genetics and a physiological psych course previously, but I had no idea how chemistry intensive basic bio courses were. My problem is, I'm absolutely useless at chemistry. While I seemed to score high grades on my exams, all of my labs were awful. What was supposed to be a crystal, turned out as brown sludge. What was supposed to change to bright orange, turned out dull yellow/green. And once my prof even had to rush my experiment to a hood because I had somehow made toxic fumes (even he was puzzled by that one). Is there any hope for me in any sort of public health or research related field, or should I just suck it up and go back to being a paper-pushing desk jockey?



Veronica writes:

Hello Dasher and Dancer Donder and Blitzen.. I mean Vince and Dixon!

I am a new listener and loving your podcast. I started with the renali worm and have been checking in each week and also going through your archives. Crazy fun! I have no idea what you are talking about half the time, but very impressed with the language and the fact that you both seem to know what you are talking about! I have a daughter in Microbiology and another one in Health Science and so i am hoping some knowledge will gradually seep in.. like osmosis, so that they will think I am smart.

I appreciate when you analyse and source the scientific words. Haha, and you were wondering if the mascatory secretory gel was something you buy at the drugstore! Funny! But anyway I always understand the parts about the weather and the kinds of weekends you have!

I have a query: Generally Is it correct that Dixon trusts that believes technology can solve our problems, but Vince on the other hand might feel we are moving further and further from our biological roots and this is what is causing a lot of our problems. For example D says mans job is to colonize space but V says he's too busy here on earth. D's solution to our food shortages is vertical farming a grand tech fix!

So, do you both also see this difference between yourselves? Or is that terribly simplistic? I would like to hear your thoughts about that.. if it doesn’t take you too far from your parasites.

Thanks so much for the show. veronica, from bc

Peter writes:

Dear Dickson and Vincent,

I am a recently retired biomedical scientist, having worked my entire career in hospital labs, mainly in Microbiology, but in my latter years as a manager. I have been fascinated by parasitology since I was a student, however I do not have a formal qualification in the area, other than a few lectures as part of my training. It was therefore delighted to discover TWIP, and I have been listening avidly over the last few weeks – fascinating!

I was wondering if Dickson knows of any distance learning courses in General Parasitology – I would be very interested in following such a course.

Finally, just a small point, arising from an observation made by Dickson (TWIP 33) I think the rare human thorny headed worm Moniliformis moniliformis has the Cockroach Periplaneta americana as an intermediate host, rather than a paratenic host.

Perhaps, as I listen to the next podcasts, another TWIP aficionado has already pointed this out, if so, please ignore this.

looking forward to seeing many more new TWIP’s in the future

all the best

Peter from Cavan

Tim writes:

In TWIP 54 there were a lot of pseudo apologies for Dicksons asides and I have to say no apologies are needed. I was unaware of the fascinating behavior of fig trees and their relationship to monkeys and bats. Please continue to wander off subject as the fancy strikes because it generally leads to me learning something I may have never come across any other way. I may be partial to this type of discourse as I ramble in both general discussions as well as emails so I will end this with a keep up the good work and go back to the task at hand of feeding this new calf who is waiting so patiently for me to finish up my email.

Tim Zweber
Zweber Farms

Sent from mobile device w/ a small keypad, forgive brevity and typos ; )

Niall writes:

My name is Niall and I am a recent high school graduate working on a virology research project at Rocky Mountain Laboratories (part of the NIH/NIAID) in Hamilton, MT. Dickson may also be interested to know that I am an angler and my father is the local fisheries biologist working for the state. As such, I have heard a fair bit about whirling disease and would like to hear more if you haven't already done a show on it. Also, I have a quick question to ask you both. I will be attending Montana State University next year and majoring in microbiology. I am undecided as to what field of microbiology I will go into but have been intrigued by the following; virology, parasitology (especially of the Neglected Tropical Diseases), and the microbiome. I was just wondering if either of you had some tips or advice for an aspiring microbiologist. Anything helps.
Thank you both a bunch. I am a big fan of TWiV, TWiP, and TWiM and would love to hear what you have to say.

P.S. I just talked to my boss here at RML and apparently he knows Vince. His name is Marshall Bloom.

Student Intern
Tickborne Flavivirus Pathogenesis Section
Laboratory of Virology
Rocky Mountain Laboratories (NIH/NIAID)

TWiP 54 Letters

Tommy writes:

Hi Vincent and Dickson,

I was listening to the new episode of TWiP (episode 52) and one of your listeners wrote in asking about tree parasites. While plant parasite is not my main field of research, I have written about one such parasite on the Parasite of the Day blog - the nematode Bursaphelenchus xylophilus which causes the tree disease known as Pine Wilt.

The basis for that post was actually a PLoS Pathogens paper on the genomic characteristics of that particular parasite.

In addition, there are also numerous insects, nematodes, and bacteria that can infect plant tissue and induce gall formation. I feel that
Dickson might be fond of those plant parasites because much like Trichinella spiralis, these organisms are capable of manipulating the
architecture of the host's tissue, forcing it to grow structures that both house and feed the parasites - much like T. spiralis with its
nurse cell.

Mike writes:

Dear doctors Racaniello and Despomier,

I just wanted to write in with a bit of praise. I have been a regular listener of TWIV for over a year now, and I'm just now catching up with both TWIM and TWIP. I have to say after having listened to the episode on hook worm and the remarkable back story given by Dickson about that organism in a historical context, that I am truly impressed. I spent ten years reading about history outside of school in my youth, and I must say that I am deeply impressed by both the depth and breadth of Dickson's knowledge.

Thank you both for a wonderful show and the hours and hours of edutainment.


Suzanne writes:

RE: earthworms

They come out when it rains because they can. It's not so much that they avoid wet tunnels when it rains as they usually avoid dry ground. When the ground is wet they can come out so they do.

Jeff writes:

Hello twip hosts,

I just listened to TWIP 52 and all the emails had to do with you guys mentioning stopping TWIP. I just discovered TWIP last summer (2012), and I've caught up with all the episodes! I just wanted to let you guys know that TWIP has kept my mind constantly busy during half day hikes in the Pacific Northwest Cascades! I thoroughly enjoy the report Vincent and Dick have. I love the jokes. It is one of my favorite podcasts.

I was trained as a Chemist at San Diego State, so I have a special connection to TWIM, with the SDSU hosts that are often on there. I now live near Portland, Oregon and hike quite frequently.

I hope none of the TWI's die, and I thank you two for all your work and information you've given to thousands of people.


Rick writes:

Hello Dr. Racaniello and Dr. Despommier!

I, like many, had a sinking feeling in my stomach when cancelling the show was proposed earlier. I was refreshed to hear this will not happen! Dr. Despommier, do you know the Komuniecki's at The University of Toledo? I had the opportunity to do some work in her lab (Patricia) working with Ascaris suum. Ah, the trips to the slaughterhouse.

If I may make a suggestion for a TWIP, TWIM, and TWIV: drugs. A review of antiparsitic agents and resistance mechanisms. Likewise antibiotics and resistance mechanisms (the New Delhi metallo-beta lactamase, cfr resistance, erm resistance, effluc pumps, gyrase mutations and everything TB has). What a show(s) that would be. TWIV, well i know there are not as many antivirals (for non-retroviral infections) but why not. Then again there is no shortage of TWIV episodes (sorry Dr. D).

Thank you both so much for all of the education and the history lessons. I am always captivated by Dr. D's stories.

Best regards,
Rick in Toledo OH, patiently waiting for spring to come

Spencer writes:

Dear Vincent and Dickson,

Attached is a letter which I think represents a sad state of affairs for parasitologists, epidemiologists, physicians and particularly for patients. It is a decision probably driven purely by cost. In the past year, I have treated a patient at this hospital with amoebic dysentery. Was this patient part of the 0.3 percent? Could you address the quoted statistic about the overwhelming giardia/cryptosporidium being found nationwide?


Spencer Kroll MD PhD

Frank writes:

Dr. Racaniello,

It is 50F and sunny today in Central Illinois, with plenty of flooding in low lying areas.

I would like to start by saying Thank You for the three TWiX podcasts. I enjoy listening to them during my commutes and while I am out walking. They are helping to keep my skills in Immuno/Micro/Etc while I am busy with my medical school studies in many other topics also.

I want to point out one clarification that applies to this weeks TWiP #53. You stated that a positive PPD indicated an active TB infection. It actually indicates that the patient has been infected with TB at some point. Most individuals that are PPD positive will not develop active TB unless if there is an issue with their nutrition or immune system.

The active disease is when there is clinical or radiographic evidence of the disease. Without either of these the patient at worst has a latent form of TB. This is important to know because latent TB is virtually non-transmissible.

It is also important to note that some patients with HIV and other immune disorders that effect the T cell population will not react appropriately to a PPD test due to a lack of T cells that cause the skin reaction.

SIU School of Medicine

PS I will be at the ASM conference in Denver. Do you know where and when you will be recording any TWiXs while you are there?

Marcel writes:

Hello TWIP team,

I love your family of shows, but while listening to TWiP 53, I noticed that Dickson used the word Eskimo. I hate to play politically-correct police, but Eskimo is now considered as fairly derogatory (at least in Canada and Greenland). The word, meaning "eaters of raw meat" by some accounts, has been replaced here by the word Inuit.

Just something to consider. Love the show!

Marcel in Canada

Justin writes:

I bought crabs from a local grocery (Pathmarket ) and noticed these small black ovals the size of sesame seeds (image attached and compared to the size of a quarter) on one of the legs and I was hoping you could identify this and confirm its normal and an ectoparsite. I love the show.

Thank you!

IMG 20130426 231444

TWiP 53 Letters

John writes:

Dear Vincent and Dickson,

I just heard your most recent TWIP. Please keep these podcasts going! I love listening to your podcasts and hearing your enthusiasm for my favorite biological topic, parasites. Remember that for every fan that takes the time to write to you there are probably 20 other fans who have not written. Plus many "new" fans are still catching up on the archived episodes (I began listening to TWIP at around episode 35 and it took months to catch up). These podcasts make an excellent teaching tool and I certainly plan to incorporate them in my Parasitology courses. And they expose the parasitologist to other areas of research that they may not otherwise have explored.

Let me suggest some topics and guest for upcoming shows.

Parasites and behavior: You've touched on this, but I think the topic deserves its own show. I recommend asking Janice Moore at Colorado State.

Parasites and Ecology: Again, you've touched on this topic (especially in episode 44), but it left me wanting more. I recommend asking Kevin Lafferty at USGS and Tommy Cheung at UNE (who has written to you previously)

Insect parasites: parasitoid wasps would be fun to learn more about. You could also focus more on fleas and lice as parasites (as opposed to vectors of parasites).

Plant parasites: not my area, but it's something I'd like to learn more about.

John Janovy teaches Field Parasitology at the Cedar Point Biological Research Station at U of Nebraska. I'm sure he would enjoy being a guest on your podcast.

And Shelly Michalski would enjoy talking about her work with FR3.


Saint Aardvark the carpeted writes:

Hi there -- I came across TWiP, TWiM and TWiV recently after following
a link from this article:

I downloaded the episode and was aghast...the idea of volunteering for a norovirus study was incredible. The entire episode was fascinating.
I could not stop listening, and ran around afterward telling everyone about what I'd learned.

I've added all three of your podcasts to my regular listening, and will be catching up on old episodes as well. I'm not a scientist, but
an interested amateur, and the level of detail is great -- I'm learning a lot, and I'm challenged to learn more. The atmosphere is
great, the guests are wonderful, and for the record I *love* the digressions and the weather reports...they make it feel comfortable
and casual.

I'm sending this to TWiP because I just listened to the episode about malaria and was sad to hear that you're considering giving it up.
Please don't! The episode was fascinating, and I'm currently downloading more back episodes. I hope you continue to produce more.

Thank you very much for your work, and the generosity of you and all your guests.

Tom writes:

A few months ago my wife asked me to look at and photograph a moribund grasshopper lying atop the leaves of a bush in our front yard.

It appeared to me that it was a grasshopper covered with eggs. My wife wanted no more such grasshoppers fearing they might eat some plant she treasured in our garden. I knocked it to the ground and stepped on it and the kicked it under the bush.

I did immediately send the photo to my friend who has a Ph.D. in entomology and she informed me that those were NOT eggs but a rare form of grasshopper mite. The mites had infested the grasshopper and killed it by sucking its vital juices. She wanted to know if I could find the dead grasshopper and stick it in a Zip-Lock bag and cool it with dry ice and give it to her. She had contacted the leading mite expert in the USA, I think some fellow in Michigan, who said he could only identify the species with certainty if he had one to examine.

By this time it was the next morning and while I did find the grasshopper's remains, alas, the mites were gone I suppose because the grasshopper was dead and no longer capable of giving them a delicious meal. I did provide her with the carcass with the hope that there might be a mite or two left on the carcass, but apparently there were none present.

Have you ever studied or become aware of mites of this type before? I did learn there are grasshopper mites but the common one[s] look nothing like these.

You just never know when you will find something rare.

I have added photos to my flickr account that you might enjoy, as you did last time I mentioned this site to you:


I have also attached a beaver I photographed a couple of days ago in one of the ponds near my house.


Rie writes:

Hello, professors. This is neko from NZ again.

I just listened to twip episode 50. You mentioned you haven't got any email and you might stop your podcasts. Now that you've mentioned it, I can imagine your mailbox is overflowing with email from all over the world, but here is another one, from land of the long white cloud.

When I started listening to twip, I was fascinated but also couldn't help feeling uncomfortable. I used to love steak rare but I no longer feel like risking it. I can't help but cook them well done for my family now. I now wash my hands and cutting boards often with detergent after handling raw meat. On the other hand, I can eat pork without hesitation after defrosting. All thanks to your educational podcasts. If you are looking for some ideas for future episodes, I'm really interested in food safety, just every day risk factors and preventive measures, associating with parasites.

At the end of episode 50, you talked about toxoplasma. One of my favourite podcasts from Japan mentioned toxoplasma being able to manipulate some neurotransmitter in the brain. I think he was talking about this article.

That Japanese host said that toxoplasma might be responsible for some suicidal cases if this article is true. That, the people committed suicide might have been infected by toxoplasma. He was wondering weather it will bring down the suicidal rate if we systematically carry out a test to find the infected and treat them. What are your thoughts on that?

Lastly, I don't mind if it's monthly, or bi-monthly, but please do continue educating us.

Thanks always,

Alexandra writes:

Dear TWIP,

I recently wrote to TWIV to express my admiration and ask a question about viruses of fungi. However, I have not previously written to TWIP, though I listen to it almost as often.

I am an undergraduate, and I work as a tutor for the biology survey class which all new biology majors must take. We're currently covering Biodiversity, and I cannot express to you how fabulous it has been to be able to enliven our discussions on Phylums Nematoda, Platyhelminthes, Apicomplexa and so on with the stories I've gleaned from TWiP. I take a particular (perhaps a little sadistic) pleasure in relating the story about how outhouses perched over lakes and rivers led to endemic fish tapeworm, or how toxoplasma gondii can cause radical behavior changes in rats (and maybe humans).

Every now and then, I even manage to turn on another person to TWiP, TWiM, and TWiV. Keep up the good work! You help to remind me of the inherently joyful and curious nature of science - which undergraduate coursework often obscures or obliterates entirely.

Peter writes:

Hi guys.
Another tool for field work.


202 specimens of Astronotus ocellatus (Oscars), were collected from a freshwater lake in the state of Amapá, northern Brazil.
A total of 6,308,912 parasites belonging to 11 different taxa were found. Protozoa was the most abundant; flukes, worms were also prevalent and abundant.

No Amazon sushi for me. 

I used to keep Oscars. Didn't realise the parasitic load would be that high.

In relation to parasitic species being 40% overall.
The link also examines the notion of the food web and the role of parasites.


peter w

Jim writes:

See for the latest, and you can go back to this one if you wish...

Oh - and thanks for the continuing podcasts, too!

Yet another Jim from Virginia

Maureen writes:

Another innovative idea used in Africa:

Scientists diagnose intestinal worms -- using an iPhone microscope

Robin writes:

also: How to pronounce Shankar. It's a name widely recognised in India. The first pronunciation is the Indian one, the second is akin to the way the British overlords butchered the local languages.

Robert writes:

Dickson's first two choices of people he would like to meet (Lincoln and Darwin) shared a birthday, February 12, 1809.

All the best,

TWiP 52 Letters

Jason writes:

Hi Drs. Despommier and Racaniello,

This week you wondered why the immune-activating receptor for Toxoplasma gondii, TLR11, is present in mice but not in humans. You noted that it looks like there's no selective pressure keeping it around in us and it has become a pseudogene. You asked why mice then need it since it doesn't harm the host.

Is it possible that rodents need extra defenses against T. gondii because it changes their behaviour and makes them more susceptible to predation? "Toxo" could be killing the mice indirectly. We descended from tiny crawly things, but when our ancestors moved up the food chain, they wouldn't need this defense any more. If it is true that T.gondii increases your risk of auto collision then perhaps we will see a selective sweep over the next million years!



Houston, TX

Kim writes:


I just finished listening to TWIP 50 and got sad when you guys were partly demoralized to continue the series. I would like to suggest you merging TWIP and TWIM, to make the burden of making these excellent podcasts a little less exhausting.  You could find a parasitologist every now and then (if Dickson is not availabe) and speak about these things in a larger group. For example Elio would probably know something and Michael, as he seems to have knowledge about almost everything! This could be embedded with doing like a ratio of 1:3 with bacteria (meaning every fourth podcast on parasites or so). Please consider this, as I object to quitting the series but am also worried about Vincent’s mental health with his work-burden!

I would also love to hear Dickson explain the vertical farm-thingy. The name is pretty obvious what it is, but a little more in depth. The book is on my list of books to buy, but I have still a few to read before buying new ones so I would like a little preview!

Thank you for the great podcasts.

Best regards,

Kim, biomedical undergraduate from Stockholm.

Jan writes:

Hello doctors,

Just a thank you from the Netherlands. I'll keep listening. And if you could do an episode on tree parasites (with external expertise ) I'd be ever so grateful. I never took any biology in school, but I can still understand the podcast ( I am a science nerd though ). What is your opinion on Carl Zimmer"s Parasite Rex ? It seemed quite accurate to me, and is very well written, but I'm no expert. Would you recommend it to the general public?



PS Majored in medieval history, now a tree-worker

Maureen writes:

To Our Esteemed TWIP Duo:

I waited with bated breath for #50 TWIP for a month. TWIP is my favorite of the tri-TWIs! Imagine my dismay when the discussion at the end of it was about whether you should end TWIP (I listen to the end). We are listening!  We just didn't write because there was no TWIP to write about for a while. I find TWIP to be the most informative and comfortable to me. Vincent and Dickson have a great rapport. I work in infectious disease with patients with Toxoplamosis, Leishmaniasis, Lime disease, Malaria, Loa Loa, Strongyloides, Giardia, etc., and always look to understand these parasitic diseases better. Your discussions clarify so much for me so please keep TWIP. I would like a TWIP that includes information regarding Sarcocystosis. Long live TWIP!


Clinical Research Nurse

Justin writes:

Good morning Dr. Depomier and Dr. Racaniello,

I listened to episode 50 on Monday, congratulations, and nearly had a panic attack when I heard that the show may come to an untimely end. I have not listened to all the episodes but have been listening sind late summer early fall and always excited to listen though as of yet I don't understand much about parasitic life cycles. Anyways, my contribution to saving TWIP is proposing a topic that I would like to see discussed. Chagas disease recently trended on the news and twitter and I thought it was pretty cool. I know you have discussed T. cruzi before but here are two links I'm interested in, a news article. and the corresponding paper

Thank you and God save the TWIP

Mabry writes:

first - to let you know how much i am enjoying your podcasts.  my husband steered me your way with #38 about dracunculiasis. i am working my way though all them now  while i am quilting on my sewing machine. then i will go through the viruses.  i was trained as a chemist; my biology education has just been picked up over the years (many now).  this is a great way to learn, and you two are fun to listen to.  thanks

second - i have great-grandparents who left the mississippi valley for oregon in 1845 & 1853 because of malaria.  in one family account, one was so sick from it that he could only lay in the wagon for the first month of the trip.  (as an aside - can you imagine walking all the way from iowa to oregon?)  i have heard that one/perhaps the major reason why we don't have malaria in the u.s. now (and italy & other places) is that because of our mosquito eradication programs, principly with ddt, we dropped the human resevoir of the disease enough so that there is not enough to propagate the disease.  we certainly have drained a lot of swamps. that helps, but i doubt that it is the answere. mosquitos will always still have more than enough places to breed. i know that ddt had a bad rep, justifiably so.  but it broke the cycle of transmission, and then it was no longer needed.   what sort of studies have there been on transmission rates vs rates of infection in the population vs the others transmission factors?

Trudy writes:

I love this podcast.  I learn so much from you two...just listening to #50.  Will be thinking of what other topics or papers might make an interesting episode.  Was very excited to see that there was a new episode!  I am subscribed via the iPhone and iPad podcast app.

All the best from a fan in Naples, FL


Rufus writes:

Yes, I'm still listening.  Fine episode.

I think I now know a bit about what complement is.


Portland, Oregon.

Nick writes:

What is your guys' favorite parasites and why?


Neal writes:

Dear Vincent and Dixon,

I am not too proud to beg.

Don't stop TWIP-ing.

I am a recent devotee to all things TWIx.  Love it.  

You have made my commute much more productive; like a journal club while I am behind the wheel.

I just listened to TWIP podcast 50.  My colleagues work on Factor H and Neisseria (maybe good for a TWIM podcast); so I found this mosquito/malaria/complement business was very cool.  Of course, mosquitos have their own complement C3 like factors that are involved in controlling malaria.  Maybe complement is the achilles heal for this parasite that we should think about more?

As an "insect immunologist", I am looking forward to listening to episode 51.  Lost of great mosquito immunology that you might consider for TWIP.

Don't stop TWIP-ing.  If you build it, they will come.

Keep up the great work!



P.S.  I won't tell Shankar that you butcher his name.


Neal Silverman Ph.D.

Professor & Research Director

Division of Infectious Diseases and Immunology

Department of Medicine

University of Massachusetts Medical School

TWiP 50 Letters

Alaric writes:

Hello Vince and Dick,

I just found your podcast and I love it! You have some wonderfully witty banter.

I am only on my 4th episode (that's what you call a podcast segment right?), and have a question pertaining to my original reason for searching out your podcast.

I am working on the research portion for a short story I am wanting to write about what the world would look like if we knew exactly how different parasites effect behavior. Think of it as a thought experiment dealing with the nature of environmental determinism and the concept of free will. Say, would people purposefully expose themselves to a parasite for a desired effect, or use one as an alibi for an act of bad faith? I may bring in epigenetics into this story as well, but I'm not sure how it will fit. It is meant to be science fiction with a bioethical slant.

Importantly, I don't want it to seem too sensationalist though, so I am trying to base as much of the story in reality as possible. Hence listening to your podcast! Do you have any suggestions on where I should look for information about this? Do you have a podcast/episode/segment about this? It's validity as an idea? Conspiracy theory or reality?

Also, love the mini-history lessons. Myself, I am a student of history of science/medicine/technology and seriously appreciate it! A++ will listen again.


C. Alaric

Robin writes:

If he is of Indian origin, the first name is not pronounced as in chancre

But as:

Robin writes:

Minas in Portuguese means ‘mines’.

James writes:

Hi folks,

You wanted to know how many NZ listeners you have so now you know you have one more. :p

Keep up the great work.

Kind regards,
New Zealand

Jacob writes:

Hi all,

I saw this in my inbox this morning and thought that it would be a good TWiP pick of the week.



Peter writes:

Dear Vincent and Dickson

I thought that this paper from PLOS one would be worth a mention on TWiP

Tapeworm Eggs in a 270 Million-Year-Old Shark Coprolite

The fossil from Brazil has been found to contain the oldest known examples of tapeworm eggs.

The specimen was so well preserved that a worm larva could be seen in one of the eggs.



TWiP 49 Letters

Jim writes:

Professors, you've discussed this idea before, but I thought you'd enjoy this nice summary from Nature:

And I do enjoy your podcasts. Thank you for sharing your wonderful conversations!
Sincerely, another "Jim" from Virginia

Alan writes:


Virginia writes:

I've been fascinated with parasites for years, ever since reading Peeps, a novel by Scott Westerfield. While it is fiction, every other chapter focused on a particular parasite and described its life cycle.

When I found this podcast, I nearly burst from happiness! While I am no longer a wildlife biology student (I recently switched to an English major - what a change, eh?), I still love learning more about parasitism. So many people find it odd that I'm so enamoured with such "gross" creatures, but I think they're just nifty.

Anyway, I just wanted to thank you for starting this podcast. It is both informative and entertaining. Keep up the excellent work!

Ethan writes:

Saw this and it instantly reminded me of Dickson's heavy breathing in the background.


Don writes:

Dear Sirs.
I became intersted in parasites of the gills in fresh water fish, esp Myxoma fundubli, and was surprised to learn tha this animal produces spores. How common is that? Your TWIPMV is marvelous, thank you so much.

Spencer writes:

Dear Vincent and Dickson,

Here's a link to an interesting study published in the Journal of Clinical Endocrinology and Metabolism that was done in China suggesting that schistosome infection may curb diabetes risk. The researchers detected an association between previous schistosome infection and a lower prevalence of diabetes in patients. This may hint at a link between glucose metabolism and T cell mediated cytokine secretion. Before I tell patients to go seek out schistosome infection, perhaps more studies need to be done.

Association of Previous Schistosome Infection With Diabetes and Metabolic Syndrome: A Cross-Sectional Study in Rural China

Spencer Kroll MD PhD

Noor writes:

I apologize in advance for the large volume of correspondence, and for not knowing the entire catalogue of what has and has not been covered. I send these e-mails with only the utmost respect and admiration.

I was so ready to roll my eyes into the back of my head for that story, but found myself captivated. I believe I sense the gift.

Also any chance of exploring the facts of the great Candiru myth?

From Wikipedia:

William S. Burroughs wrote about the candiru in his 1959 novel Naked Lunch, describing it as "a small eel-like fish or worm about one-quarter inch through and two inches long patronizing certain rivers of ill repute in the Greater Amazon Basin, will dart up your *censored* and hold himself there by sharp spines with precisely what motives is not known since no one has stepped forward to observe the candiru's life-cycle in situ."[22] Burroughs also mentioned it in The Yage Letters: "At that time I was stationed at the remote jungle outpost of Candiru, so named from a tiny eel like fish that infests the rivers of that area. This vicious fish introduces itself into the most intimate parts of the human body, maintaining itself there by poisonous barbs while it feeds on the soft membranes".[23] The fish is also referred to in David Grann's The Lost City of Zand in Chuck Palahniuk's Fight Club (novel).

Not knowing anything about its reproductive or life cycle, its difficult to say if this should be classed a predator or parasite, but in my book anything that "allegedly" swims up your urethra and needles itself in there permanantly should be classed a parasite, although one that certainly shows no regard for the life of the host, although I'm sure there must be surgical interventions to prevent kidney rupture.

It should also be noted that the Candiru is a major plot point in the Season 1 Episode 9 of the animated Adult Swim show "The Venture Brothers" entitled "Are You There God? It's Me Dean."

The episode appears to have been available for free some time in the past, but is now certainly $2 on iTunes.

Being a Johnny Quest kid I have a special place in my heart for The Venture Brothers.


Robin writes:

With regard to TWIP & TWIM & TWIV: Keep 'em comin' !

Possible reservoirs in a vertical farmer:

Many hares
Ten little piggies.
Two soles.
Two calves.
A large variety of ducks:
Thoracic, R lymphatic
(R & L & common) hepatic, (cystic & common) bile, pancreatic etc.

Visceral pain:

All viscera except the central nervous system have pain receptors. They are activated by stimuli appropriate to the organ, which are not necessarily the same as the stimuli for somatic receptors. The intestine can be cut with a knife without pain, but just about everyone has experienced the pain from stretching of the gut. The pain receptors in most solid organs is located in their (fibrous) capsules, and are stimulated by ACUTE stretching or ACUTE inflammation.

Insects, bugs & arachnids:

It was quite clear to me in school that all bugs were insects, but that not all insects were bugs. I would not have graduated if I were not clear on that point. I had to unlearn English after coming to the uS of A (lower case "u", as that is the way it was originally intended, in the Declaration of Independence).
Likewise, I would not have graduated if I had lumped ticks and mites with insects. But of course in the uS, one must not expect to hear about Medical Arachnidology.

Mosquito swarms:

In my childhood, I remember swarms of male mosquitoes swirling above the heads of people in the evenings. One knew that they were male because they had mustaches (feathery antennae). Therefore one was not concerned about being bitten by them.

TWiP 48 Letters

Ruth writes:

Dear Dick Despommier

My name is Ruth
I am a listener of twip and recently I decided to look into your vertical farming that you mention on the podcast.

While I was watching a video of you explaining vertical farming you mentioned soil-less growth in an urban environment and I immediately thought of another video that saw earlier this week.

The video is about a man named Eric Maundu - who combined aquaponics with fish farming in an amazing way. Using a very small amount of space he set up a system with a fish tank . The fish water with the fish waste is carried on a basin of rocks (in which sit plants). Bacteria break down the fish waste and the plants use the nutrients. Afterwards the water -minus the waste is returned to the fish tank. Maundu also mentions that the fish could be edible types - so you could grow two resources at once.

I just thought it was so amazingly efficient and thought you may be interested also.

Here's the link to the video .

Also I would like to thank you and Vincent very much for This Week in Parasitism and this week in virology - both wonderful entertainment and education :)


Maureen writes:

I'd like to learn more about sarcocystis, a parasite that usually only affects animals but seems to have infected some of our military.

Carl writes:

To: This Week in Parasitology podcast (Vincent Racaniello, Dickson Despommier)

Here's evidence-based advice for cat owners unwilling to get rid of their pets:

" litter should be changed daily, and pregnant women should delegate this task to others.

"Many scoopable cat litter manufacturers suggest scooping fecal lumps daily and changing litter weekly, but this is likely to give a false sense of security because the oocycts might sporulate in the leftover feces; in addition, the scooping spoon is likely to become contaminated with oocysts; hundreds of oocycts may be present in a milligram of infected feces. There is also the risk of cats tracking infected feces throughout the house.

"We do not currently have a practical recommendation for safe disposal of cat litter other than disposing it in a heavy duty plastic bag with the hope that anoxia will kill T. gondii oocysts."

Dubey et al: Survival of T. Gondii in Cat Litter.
Journal of Parasitology, Oct 2011 at 753.

"Gloves should be worn while gardening, while changing litter and while handling soil potentially contaminated with cat feces.

"Owners may also be advised to keep dogs away from the cat litter box to prevent ingestion of and passage through of oocysts.

"Vegetables should be washed thoroughly before eating, because they may have been contaminated with cat feces."

Dubey: Toxoplasmosis of Animals and Humans,
2d ed. 2009 at 54.

Practical suggestions:

Here's what I'm doing with 3 cats my wife insists on keeping:

Using a small open litter box, arrange a big plastic bag covering the bottom and extending up over the sides. Add the litter. At least once every 24 hours, wearing disposable examination gloves, lift the bag containing all the litter, knot the top and take it outside to the trash container. (No scooping.) Replace bag and litter.

We switched to pine pellets for litter, which is much cheaper--especially from farm or horse supply stores.

Public health risk:

Although most vets believe that cats shed oocsyts once for a few days, the leading researcher says, "Whether naturally infected cats shed oocysts more than once in their life is unknown."

Dubey: Toxoplasmosis of Animals and Humans, 2d ed. 2009 at 36 - 39.

While everyone was skeptical of the initial reports of brain cysts leading to mental illness and car crashes, the more recent research has made such claims more plausible. Given the limits of research tools and funding (and how small oocysts are and how hard it is to evaluate brain cysts...), it seems prudent to minimize our individual risk of toxo from cats and encourage more effective public health efforts (like changing the labels on cat litter.)


I assume you've been trying to get JP Dubey on your podcast. Please
keep trying....

TWiP 47 Letters

Liesbeth writes:

Tomorrow starts the XVIII International Congress for Tropical Medicine and Malaria Conference here in Rio de Janeiro. I read Peter Hotez will be participating in a round-table session on “What is the future role of academic journals in the research, control and prevention of tropical diseases?”.I myself will be presenting partial results of my graduate project on the zoonotic potential of Giardia duodenalis in the past. Dr. Racaniello recently participated in the Brazilian Virology Society meeting congress in São Paulo, but what about Dr. Despommier? It would have been awesome meeting you both here! But well, too many congresses, too little time, right? (and money, for that matter!)

All the best


Sophie writes:

Hello Twipsters

I have a pick of the week: Windowfarms, it's a non-profit vertical gardening project: How to make your own vertical window garden. If you want a full description listen to Britta Rileys TED-talk, I can't do it justice. I don't know if this is a fitting pick, as it's more a Dickson pick, than a parasitology pick. But I think it is amazing, I'm definitely doing this:)

Keep up the good work

Peter writes:

Dear Vincent and Dickson.

I would like to point out that the "Female Owners of Cats More Prone to Suicide" article mentioned in TWiP 43 is rather misleading. The study mentioned made no mention of cat ownership and men were not included in the study as it was only mothers who were included in the cohort.

Most human infections are from contaminated meat, not from handling infected cats.

If a cat is infected with Toxoplasma gondii the oocysts are only shed for a short period of time, typically less than 14 days, before the cat's immune system stops oocyst production. The cat should then be immune to further infection.

Dr Postolache has noted limitations to the study, such as the inability to determine the cause of the suicidal behaviour.

He said:

"T. gondii infection is likely not a random event and it is conceivable that the results could be alternatively explained by people with psychiatric  disturbances having a higher risk of  becoming T. gondii infected prior to contact with the health system.”

Could the high rate of infection reported in France be due to the popularity there of rare meat?

Further information on Cats and toxoplasmosis:

Peter writes:

Dear Vincent and Dickson.

Thank you for a fascinating and informative TWiP, I thoroughly enjoyed the linking of parasitism and ecology.   Following your request for listeners to find more information on the life cycle of  nematomorphs I did some reading and found that many nematomorph species use a "paratenic" or transport host in which the larva forms cysts and do not develop further until the paratenic host is eaten by a scavenger or predator.(1)

Crickets are generally omnivorous but some species are carnivorous. A wide range of species can be used as paratenic hosts including flatworms, snails ans some nematomorph species make the transition from water to land by forming cysts in aquatic insect larvae, with the cysts surviving the host's metamorphosis to an flying adult which can then convey them to land. Adult nematomorphs are short lived and do not feed, they die after mating. One species of nematomorph has been  discovered from Kenya that is parthenogenic and lacks males(2) Some sites I looked at mentioned the morphological similarity of the larval nematomorphs to some adult marine worms(3)





continuing: I came across a bit more information on  how  nematomorph worms  influence insect behaviour.

David Biron,  Frédéric Thomas and  colleagues at the  Laboratory of Genetics and Evolution of Infectious Diseases at Frances National Scientific Research Center in Montpellier., France, have found the worms produce proteins that mimic some found in the insects nervous system. Somehow these prompt the insect to jump into water, allowing the adult worm to swim away.

Tommy writes:

Dear Vincent and Dickson,

I really enjoyed your episode on the horsehair worm and food web ecology. In case if you haven't already found it, here is a review on the biology of nematomorphs which you might find useful:

Hanelt, B., Thomas, F., and Schmidt-Rhaesa, A. (2005) Biology of the Phylum Nematomorpha. Advances in Parasitology, 59: 243–305

Also, I was pleasantly surprised to hear you talk about the New Zealand cockle-trematode system. Those papers you mentioned originated from the lab where I did my PhD - in fact, my PhD thesis (and a small part of my postdoc work) consisted of research which followed up on some of the questions which were raised by those initial studies you cited, delving deeper into the ecology of that host-parasite system. Here are a small selection of publications which pertain specifically to the cockle-trematode system.

Leung, T.L.F. and Poulin, R. (2007) Interactions between parasites of the cockle Austrovenus stutchburyi: Hitch-hikers, resident-cleaners, and habitat-facilitators. Parasitology, 134: 247-255.

Leung, T.L.F. and Poulin, R. (2007) Recruitment rate of gymnophallid metacercariae in the New Zealand cockle Austrovenus stutchburyi: an experimental test of the hitch-hiking hypothesis. Parasitology Research, 101: 281-287.

Leung, T.L.F., Poulin, R. and Keeney, D.B. (2009) Accumulation of diverse parasite genotypes within the bivalve second intermediate host in the digenean Gymnophallus sp. International Journal for Parasitology, 39: 327-331.

Leung, T.L.F., Keeney, D.B. and Poulin, R. (2010) Genetics, intensity-dependence, and host manipulation in the trematode Curtuteria australis: following the strategies of others? Oikos, 119:393-400. Leung, T.L.F. and Poulin, R. (2010) Infection success of different trematode genotypes in two alternative intermediate hosts: evidence for intraspecific specialisation? Parasitology, 137:321-328.

Leung, T.L.F. and Poulin, R. (2011) Intra-host competition between co-infecting digeneans within a bivalve second intermediate host: dominance by priority-effect or taking advantage of others? International Journal for Parasitology, 41: 449-454.

Vincent was wondering how the cockles become infected with the trematodes - I can answer that as I conducted (and came up with the protocols for) experimental infections of those cockles, and spent many, many hours observing and documenting the process. The free-living cercariae are initially sucked in through the cockle's inhalant siphon, once inside the cockle's mantle cavity, they immediate cling to the foot and begin penetrating into the muscle. Once within the foot, they then migrate through the muscular tissue for some time (a few hours at most) before encysting at a suitable spot (usually the tip of the foot). During one of my observation periods, I recorded some footage of the cercariae penetrating the foot tissue - the link to which I recall I've sent to you in another e-mails, but to save you the trouble of wading through masses of old e-mails, here it is again:


P.S. I really appreciate all the effort and time which must go into making all the "This Week In" podcast series and the role they play in educating the public about the unseen and overlooked majority of life on this planet. I am the writer and co-administrator of the Parasite of the Day blog (, where I write about newly published research on parasites that I happen to come across, in a manner that is accessible to the general public. I consider that my small contribution, as a scientist, for public education and promotion about parasites, parasitism, and parasitology.

Robin writes:

A Conversation with Robert Sapolsky

A few years ago, I sat down with a couple of the Toxo docs over in our hospital who do the Toxo testing in the Ob/Gyn clinics. And they hadn't heard about this behavioral story, and I'm going on about how cool and unexpected it is. And suddenly, one of them jumps up, flooded with 40-year-old memories, and says, "I just remembered back when I was a resident, I was doing a surgical transplant rotation. And there was an older surgeon, who said, if you ever get organs from a motorcycle accident death, check the organs for Toxo. I don't know why, but you find a lot of Toxo." And you could see this guy was having a rush of nostalgic memories from back when he was 25 and all because he was being told this weird factoid ... ooh, people who die in motorcycle accidents seem to have high rates of Toxo. Utterly bizarre.

What is the bottom line on this? Well, it depends; if you want to overcome some of your inhibitions, Toxo might be a very good thing to have in your system. Not surprisingly, ever since we started studying Toxo in my lab, every lab meeting we sit around speculating about which people in the lab are Toxo-infected, and that might have something to do with one's level of recklessness. Who knows? It's very interesting stuff, though.

You want to know something utterly terrifying? Here's something terrifying and not surprising. Folks who know about Toxo and its affect on behavior are in the U.S. military. They're interested in Toxo. They're officially intrigued. And I would think they would be intrigued, studying a parasite that makes mammals perhaps do things that everything in their fiber normally tells them not to because it's dangerous and ridiculous and stupid and don't do it. But suddenly with this parasite on board, the mammal is a little bit more likely you go and do it. Who knows? But they are aware of Toxo.

Don writes:

Dr. Racaniello,

On TWIP 42 you decried the lack of a Microbe World search engine.  Well here's a little used Google feature that can help.  To find the TWIP episode about toxoplasma simply type this as a Google search: toxoplasma "this week in parasitism"

As long as the site allows the Google crawlers the result is usually better than site search features.  Unless of course the site search feature is an embedded Google search.

Looks like the TWIP you were looking for was #12.

Love TWIP, TWIV and TWIM.  I have heard them all.  Some multiple times.  But my favorite has to be TWIP largely because of the happy accident of a world class parasitologist and a world class raconteur being embodied in your co-host.   Dickson Despommier is without peer.

Dickson's modest erudition and your nagging straight man routine make for a very entertaining show.  Please don't think I am belittling the part you play.

That you could do what you do so graciously, given all your accomplishments, is rare.  Lesser men would let their egos get in the way.

That I can also learn something is also much appreciated.  Don't change a thing.

Thank you, Don

Kyle writes:

Dear Dr. Despommier,

I am a student doing post-bac work in premed, and was intrigued by your discussion of a possible study of the contamination of dog run soils by Toxocara Canis.  I'm designing a study in the Chicago Land area to gather this data, and was wondering if you could recommend a method of testing for eggs in the soil, i.e. if there is any preferential methods in your opinion.  Also, I heard on your podcast that there is some graduate work being done in New York, and was also wondering if they would want to compare data after both our studies are done.  Thank you for the great work both you and Dr. Racaniello put out every week, your podcast is an absolute joy to listen to.

Sincerely, Kyle

Ronald writes:

I love your TWIP and TWIM and am sharing a balance of them with students as time permits. My absolutely only complaint is that ... as an old geezer ... my hearing is not what it once was and for me ... there are often times when a speakers' voice seems to almost disappear ... sort of a mumble for me ...  I believe this is because you speak ... and this is natural ... as if you are speaking to someone sitting close to you. I believe it would help if you each spoke as if you were speaking to an audience ... maybe with a microphone and never allowing your mouth to point away from the audience ... aiming the sound down instead of forward ... without losing the cordial atmosphere. Trivia, I know and I doubt anyone else has described similar issues. Keep up the great work. It is great to have a chance to learn from your discussions. I know you spend a lot of time preparing these and I am truly grateful. Enunciate is the word that has been escaping me but I believe that is the core of my problem.


Nick writes:


Firstly I'd like to say I am a huge fan of your shows- TWIP, TWIV and TWIM. I am a student in Perth, Australia and am in the final year of my zoology major, and first year of my microbiology major. I am extremely interested in getting some experience in a lab to do with viruses, parasites and microbiology, so I was wondering if there was any help or advise at all you could give me?

Thanks, Nick

Amanda writes:

Good morning Drs. Racaniello and Despommier;

My name is Amanda and I just love your TWIP podcast.  This article caught my eye and I thought it would be of interest to both of you considering that it seems to be about a virus parasitizing another virus!

Also, a recent study on DNA methylation in Trich:

Keep up the good work!   Can't wait to hear another podcast…you guys keep my brain active when doing routine lab tasks!


Research Technician at Massachusettes General Hospital

Jim writes:

FYI for Dick just to show where the subject is appearing, with comments.

Jim Smithfield, VA

Singapore Builds First Vertical Vegetable Farm

via Slashdot by samzenpus on 11/5/12

kkleiner writes "Short on arable land? One solution would be to plan up. Singapore, a small country that imports most of its food, has now begun selling vegetables from its first vertical farm. And even while they're more expensive the vegetables are already selling faster than they can be grown. If the farms prove sustainable – both technologically and economically – they could provide a much desired supplement to Singapore's locally grown food and serve as a model for farming in other land-challenged areas."

Michael writes:

Dear Professors Vincent Racaniello and Dick Despommier,

I am a long retired biochemist who spent his career in Public Health. The two things that I miss the most are access to journals, and the round table discussions that I held in my office every morning. I accomplished this by providing free coffee, and often Danish. Soon my office was bursting with those wishing to talk about what they were doing, where they were having problems, and what they were going to do about them. These were not meetings in the normal sense, but rather verbal free-for-alls where many problems were resolved, many friends made, and aptitudes which were dormant came alive.

While I often worked with the biochemistry of microbes, I never had occasion to do any work with parasites other than see an interesting slide or specimen that someone wanted to display to everyone in sight. When I started listening to TWIP,  I first I thought it was the filling of an enormous cavern of personal ignorance that drew me towards your show. But then I realized it was the Socratic method that formed the backbone of your lectures. With Professor Racaniello so often playing the foil, and the general banter it was almost like being back at my favorite time of the day at work. As I now live in a rural area and can no longer have such conversations with my old colleagues, this has truly gladdened my heart and filled in a missing part of my life that goes far beyond the knowledge provided. While I realize that this is not your primary intent, it is a delightfuly serendipitous collateral benefit. I would like to urge you to ignore those curmudgeons and martinets who demand a formal, structured and pedantic presentation. You are at your best when you allow your personalities to show through.

This is particularly significant to me as I had been in an undergraduate honors program that had about 40 profs and a dozen students. We were completely self directed, and met either one on one, or in small groups with the profs. We got to know them as people, and as a result leared more and did more than we ever would have under more normal circumstances. It was unfortunate that this outstanding experiment was far too expensive to be broadened to the rest of the students.

Before I wear out your patience, I would like to note that I listen to many such podcasts, but that yours is the only one that does not request financial assistance (which I usually provide.) You program is most worthy of some mechanism of recognition. So I thought perhaps a donation in your names and TWIP to be a possible method of recognition of your outstanding work. Would you please advise me as to your favorite charity or research facility in parasitology that you would prefer the donation to be made.

Truly gratefully yours, Michael

Robert writes: Sirs, In September 1903 the British satirical magazine Punch published an insomniac's ode to the students of tropical disease:

Men of science, you that dare

Beard the microbe in his lair

Tracking through the jungly thickness

Afric's germ of Sleeping Sickness

Hear , oh hear my parting plea

Send a microbe home to me.

Sometimes it is better not to get what you ask.

Todd writes:

Thank you so much for the parasitology podcast. I am encouraging my children and nephews who will probably pursue health related careers to listen to it, first because it is such an interesting “fly through” of the related science, and secondly because I find you two so interesting. However, my family eats a whole lot of sushi, and I haven’t been able to find the sushi episode on iTunes. Did that end up getting made?

Regards, Todd

P.S. I had been imagining myself to be a sort of forager, and would eat the semi-fermented pears that fell from my tree after cutting away the portions containing ants and worms and washing them a bit,  but after watching some YouTube videos about roundworm infections, I got a little bit afraid, since I don’t know but that the pears had fallen onto soil or leaves that had traces of dog, opossum, squirrel, rabbit, raccoon, or bird feces. However, a professor friend of mine told me that our immune system kills roundworms for us, and it’s only children who are at risk.

PPS. Since I also occasionally dip into alternative health websites, I wonder if you have ever podcasted related to the “clean hypothesis” of allergies and the alleged cures of asthma and other allergies  from exposure to roundworms (in controlled situations) and hookworms in uncontrolled situations. I think a lot of people are interested in auto-immune disorders lately, and those of us who live somewhat dirty and untidy lives wonder if somehow environmental stimuli are keeping us robustly healthy.

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