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TWiP 74 letters

voxsciurorum writes:

Dear water-based life forms:

It is 24 degrees in Overland Park, Kansas and I am looking at a slide labeled "Giardia lamblia", part of a museum exhibit on water and human (over) use of water.

I see a greenish lump. I don't know if it's alive. I was not meant to be a diagnostic technician.

The exhibit is produced by AMNH and/or, and located in the Museum at Prairiefire ( It may be interesting to listeners in the Kansas City area.

Heather writes:

Hi Dr.s R & D!

I think I recall one of you mentioning a younger relative enjoying the game Plague, Inc. during a podcast somewhat recently. With this vague notion in mind I downloaded the game and have been enjoying it ever since. Normally I don't like electronic games, but this one seems to use some very accurate algorithms to simulate the spread of various real and imaginary pathogens, with the ultimate goal of the player being the total annihilation, or enslavement, of humanity. The game is played from the perspective of the pathogen and DNA is the "currency" of the game, which I thought was very clever. Most of the "science" the game is based on seems to be quite well-researched also. I think a discussion of the game, from the viewpoint of scientists who work with microbes and pathogens, would make for a very interesting TWiM or TWiV (there are many kinds of pathogens, besides parasites, including viruses. I have good luck winning with both, even on the "brutal" level of difficulty).

I have just subscribed to Urban Agriculture. I have no idea how I will keep up with four podcasts now! I have no idea how Dr. R. keeps up with four of them! I can keep on top of TWiP and TWiM easily enough, since that is my background but I sometimes have trouble with TWiV, since I only have the most elementary virology background. Perhaps a virology primer, like the early episodes of TWiP, would help me and other listeners who don't know a ton of virology?

Thanks for the great podcasts!


Tristen writes:

Dear Vincent and Dixon,

I have to tell you that I'm a huge fan of Twip and I love listening to you guys! In November 2013 I did my first medical mission trip to Nzara, South Sudan. Vincent you probably already know an interesting fact about Nzara is that it's one of the first places Ebola virus was discovered in 1976! After the short trip I enjoyed the work so much that now I am trying to find funding or sponsorship to leave life here and work in Nzara for a couple years. I appreciate how your podcasts are both educational and entertaining at the same time. My favorite one so far is when you had Peter Hotez on talking about neglected tropical diseases.

I want to request you guys do an episode about chronic malaria infection in children living in sub Saharan Africa and the connection between Epstein Barr virus and the high rate of pediatric burkitts lymphoma diagnosis. This would be a great podcast because it combines parasitology and virology! I learned about this connection after having malaria myself after my trip and find it very interesting. Thank you both for your good work and for giving me such valuable information which I can take back with me to South Sudan!


If you are interested in seeing the page about my work, visit here:

Claire writes:

Hi Dickson and Vincent,

I wrote to Twiv recently but had to also write in here to let you know that without your podcast I would have been totally lost last month when I heard a series of talks on some of the more "popular" parasites (tryps, leishmania etc). I didn't know an amastigote from a billy goat before studying up with your podcasts. Thanks for the help!
-Claire in Seattle

Jim writes:

Here's a link to a short story in our local "Daily Press" for the Norfolk area, about a museum in Tokyo about parasites. Perhaps it's provide Prof Despommier a side trip one day when he's in that part of the world. - Jim; Smithfield, VA

Museum might put you off sushi for a while

For something educational to do before lunch, I admired bottle after bottle of pickled parasites. Some frilled. Some with suckers. Most hermaphrodite. And all gross...

Suzanne writes:

I found lice in my 7 year old's hair about a month ago. My 11 year old had been asking me to check her hair for months and I never could find anything. Checking more closely with a lice comb revealed she did have them. A quick comb through my hair came up positive, too. Yay. Lucky for my husband, he keeps his head shaved.

There was a funny thing I noticed, though. I had been taking a low dose of iron daily and can pretty easily tell when I'm... eliminating... the extra and ought to skip a day or so or when it's all being used up. As soon as we shampooed and combed out the lice, I stopped using all the iron.

Remembering your comments on hook worm and anemia, I looked up lice and anemia. Google had links to a few cases where kids who were very infested showed up at doctors' offices or hospitals with severe anemia that had no other cause the doctors could find. This and the information about lice that mentioned some people have asymptomatic cases (evidently the itching is due to an allergy, not their bites) made me wonder just how long we had all been infested. I've had off and on times of slight iron deficiency since I was pregnant with my youngest and my oldest was in preschool. That's not too uncommon in women and I'm healthy otherwise. This could be totally coincidental, I know, but it's making me wonder.

I'd love to know if anyone has studied how prevalent lice are in the US. I'm starting to suspect that quite a few of us could carry them around in low numbers and not know for... maybe years? It does seem, like bed bugs, that lice are turning up more. At least around here in Central Texas where the weather is barely even worth mentioning. It's summer so it's hot. Seriously hot. But we've been getting more rain this year so that's something.

Peter writes:

Dear TWiP team,
I thought this report from The Lancet Infectious Diseases may be worth a mention:

Evidence of schistosomiasis has previously been found in 5200-year-old Egyptian mummies, that date has been pushed back a thousand years by the find of a flatworm egg in a grave at a Neolithic settlement site in northern Syria.

Piers Mitchell at the University of Cambridge and his colleagues examined sediment collected from beneath the pelvises of 26 skeletons, all between 6500 and 6000 years old. In one 6200-year-old sample they found a 130-micrometre-long flatworm egg that belonged to one of the species responsible for schistosomiasis.

More information on the Tell Zeidan site:


Rabbit writes:

I just started listening a couple weeks ago, so I'm not caught up yet, but TWiP is the best science podcast I've found. It's so hard to find resources for laymen about parasite that aren't full of misinformation. I've been teaching myself about parasites for a while (I'm autistic, and they're one of my special interests). As is the case with many subjects, it's hard to find resources about parasites that appeal to an audience that's not made up of either experts or complete novices. It's easy to find very basic information, and it's not too difficult to find academic resources, but TWiP is by far the best resource I've found for my level of knowledge.

I have a question: I've read that cat owners aren't significantly more likely to be infected with toxoplasma gondii than people who don't have cats. Is that true, and if so, why/how do you suppose that is?

TWiP 72 letters

Robin writes:

plethora (n.)

1540s, a medical word for "excess of body fluid," from Late Latin plethora, from Greek plethore "fullness," from plethein "be full" (see pleio-). Figurative meaning "too-muchness, overfullness in any respect" is first recorded 1700. Related: Plethoric.

Are birds infected?

"No" "Only warm blooded animals".

"Warm-blooded animals" includes birds.

David writes:

Dear guys,

Question, who is Spencer Wells, arose in final minutes of TWIP show I just heard, near mention of tragocytosis (sp?) and a couple of enjoyed PBS series.

Spencer Wells also had a PBS (I think) bit of his production. Must be something <ten years ago now, but charmed me so that it seems fresher than that. I've always wished to see him back with more. Wish I knew the title.

He is a geneticist, and I guess was on the cutting edge of reconstructing the origins of human dispersal. He clarified the first spread of sapiens along the South Asian corridor, ultimately to Australia. Your context was "tropical species which went where it didn't need clothes."
His bearing seemed a little (American) aristocratic, but not in an offensive way. I thought his discussion was especially smart, and I felt exceptionally well informed by the show. Is it conceivable that it was a bit too far above intellectual middlebrow to satisfy the viewing demographic? I don't know, and shouldn't even speculate, and must add that I too have enjoyed the other PBS productions you guys named. Besides, human origins has always been a favorite hobbyhorse of mine.

Anyway, the genetics-based reconstruction of human population origins has moved by leaps and bounds since, as you know, yet I haven't encountered any but snippets of detail in public productions. I wish Spencer would come back with a new show on the subject.

That's who I think he is.


PS So what is tragocytosis?

Rachel writes:

Dear TWiP Team:

In listening to TWiP episode 71 whilst gently tending my cell culture garden, I noted an inaccuracy in your classification/description of birds. In the context of the host range of Strongyloides, Vincent asks, "Are birds infected?" To which Dickson replies, "No... warm blooded animals," implying that birds are not warm blooded animals. This is a mistake that I have noted being made in previous episodes of the TWiX family of podcasts as well. Most birds are, indeed, warm blooded animals, more precisely homeothermic endotherms, as are most mammals.

A one-time point in need of clarification the same part of the conversation, which seemed to be about Strongyloides in general, not S. stercoralis specifically, is that, while it is true that S. stercoralis only seems to infect mammals, there is at least one species which does infect birds, S. avium.

Thanks for the interesting podcasts.

Rachel Tell

Rachel Tell, DVM, PhD
Postdoctoral Research Fellow
University of Iowa

Colin writes:

hi, is there a parasite known to kill all virus it encounters.
is there a virus known to kill all parasites?

Has any virus been found to have parasites yet? and if so do they have virus? and so on and on?

I know these questions may seem a little perhaps different, but what do you guys think?

Kind Regards,

James writes:

I’m not a veterinarian or a fish farmer. But I trained as a marine scientist, including a large part of my studies at the Institute of Aquaculture, and worked on the production of a vaccine. A bit of feedback concerning show TWiP 70 (which was great as always!).

Apologies if anything has been discussed across TWiX, feel free to center on interesting bits (if any).

Zoonotic or non-zoonotic invasive bodies

Just as significant, if not greater risk of invasive aquatic species likely to be through ballast water in shipping. This has already had significant impact across the atlantic. Carcinus maenas (Green crab / european crab) has been well studied and decimated your soft shelled crabs in parts of America. They hitchhiked as larvae in the ballast, which when expelled at shore to raise the height of the ship to enter so do the larvae. Conversely America then sent signal Crayfish over by the same means to pay Europe back!

This is why in Australia in addition to strict animal import rules (i.e. never, almost), ships are order to remove ballast much further out at sea in order to protect the barrier reef. As well as severe consequences for shipping firms, ship captains flaunting this will have severe consequences (non-nationals face banning from the country and it’s territorial waters- a career ender).

‘Aquaculture’ vs Rearing

Unlike True Eels, the Monopterus albus does not require migration to, for example in European species, the Sargasso Sea in order to complete it’s life cycle. However, I suspect (although I cannot find any exact confirmation) that M. albus has still yet to have it’s full life cycle closed in aquaculture. Hence the phrase ‘farm raised’ or ‘reared’ being used. In my quick search the only specific confirmation to captive either way to breeding of M albus was a negative one (, with a few US government agencies refering to ‘escapes from aquaculture farms’. But these could refer to those that escaped from a farm of another species, e.g. fish. Sorry I can’t be more specific most of my documentation is in storage in Scotland.

In Anguilla it actually still requires the capture of live elevers (young), and ongrowing in capture. They cannot be ‘bred’. Despite this is similar to the maturation of Salmon, which can have it’s life cycle closed, the closing of the Anguilla sp life cycle has still eluded scientists. I did find one reference to use of hormone treatments for M. albus, but I am sceptical barring further documentation.

DD, brisked over there being fresh and salt water eels. Anguilla anguilla (European eels), that are part of the true eels (Anguilla) and are normally fresh living but migrate to sea for spawning. European eels migrate all the way to the Sargasso sea! (satelite tracking of eels: Larvae return via the gulf stream.

The same is true for the American eel (Anguilla rostrata which also travels to sea for spawning, although the journey is less dramtic as it’s european cousin.

The whole of the Anguilla is often described as freshwater due to the greatest part of its life being freshwater.
Eels have strict protection in the UK. It means criminals try to harvest elevens at night. Leading to police waiting in the dark for them!


You mentioned polyculture. It has been known, on developing areas for pigs to be cultured in wooden sheds. On the lower level, chickens are cultured. Both floor have gaps between floorboards for the excrement to fall through to the lower level. Below the fish? It is built over rivers, so below the chickens are small fish cages!

This also kind of side arches into DD's new podcast (first episode was great) but i will save that for a separate email.

Didn’t catch many eels (100)- I can beat that!

There was a now infamous article of contamination in fish feed and effects on human health due to PCB’s. It rose to stardom due to the BBC being reprimanded for its use as part of a ‘documentary’ that was highly biased. It involved a sample of less than ten fish (five I think). It was a farmed versus wild comparison assuming feed would result in the changes on the chemical. Of the fish sampled some were from America, some UK. The ONE ‘farmed fish’ that was ordered, it turned out wasn’t even farmed (never specified when ordered). It got published and was being reviewed as part of EU policy. The blunder only got found out through coincidence of a scientist being on the EU review board also being at the Institute supplying the fish, knowing they only used wild samples of that species (and later confirmed this).

great to hear all your collective podcasts
(too warm at about 18oC)

Rachel writes:

Hello TWIP team-

I would like you to know that there are veterinarians listening to This Week in Parasitism. I am a veterinarian, immunologist, and steady TWIx listener. I have recommended all three TWIx podcasts to many colleagues, veterinary and otherwise, over the last year since I came across them for the first time. I find TWIP, in particular, is interesting to the me due, in no small part, to my veterinary training. We spent a lot of time on eukaryotic parasites, especially those with zoonotic potential.

Additional Episode 70 notes: I would really like it if you would spend more time explicitly on the non-human side of zoonoses, as you brush up against it during many episodes but rarely spend much time on it. Also, add me, along with letter-writer Heather, to the list of people who would love an episode here and there devoted to aquatic or aquaculture themes (my background is largely in the immunology & diseases of fish).

Keep up the good work, I like having TWIx in my rotation of cell-culture listening.

Rachel Tell

Rachel Tell, DVM, PhD
Postdoctoral Research Fellow
University of Iowa

TWiP 71 letters

Heather writes:

Hi Dr.s R&D,

I thought you might be interested in this news article about aquaculture in Hong Kong. Perhaps it's time for another fish parasite episode? I love the podcast, keep up the great work.


Bill writes:

Trichinella (1835-2007)

After a long and productive life, I am sad to tell you, poor Ella is gone, it seems she was always around, that she had such an infectious nature that she would never fade into history in this manner... needs an update datewise...

Your web guy can set an autoupdater for dates and copyright notices etc, so as each year passes, the year is incremented upwards. Each date you update needs to be told to the web guy, so it is included in the update and does not change the font or color.

It makes the website look fresh.

Ellen writes:

Thought you'd enjoy this :-)

Alicia Watkins' Etsy shop has many cross stitched bacteria and viruses too!

Fishpathologist writes:

Dear Doctors R&D,

I'm catching up on old episodes and I very much enjoyed Dr. D's reading from his new book. I see that his vertical farm book is in audio format, will the new book also be available in audio format? Dr. D telling "stories" is one of my favorite parts of TWiP and I would love a whole book of them.

I also wanted to tell you how far-reaching your podcasts are. My husband works coordinating volunteers for a state park. A science club from a community college in Tennessee came to volunteer in the park during their spring break. My husband was very taken with how industrious and intelligent the group was. I work managing chemistry and microbiology labs for undergraduates at a state college, so I was naturally slightly suspicious of these assertions. The students and their advisor invited us to have dinner with them and I must admit I found them very engaging young people. Due to my interests and previous work with parasites and microbiology the conversation naturally turned in that direction. One of the young ladies, who couldn't have been more than 18 years old, mentioned that she absolutely LOVED all the TWiP, TWiV, and TWiM podcasts and is pursuing microbiology as a field with an interest in cyanobacteria. I thought you would enjoy hearing how your work inspires some of the youngest of the new generation of scientists. Thank you for the excellent podcast. I look forward to more "stories" and I really like having guests like Sagi on TWiP.

Ellen writes:

Hi Vincent and Dickson,

I enjoy the TWIP podcast as someone who's interested in science so please excuse me if bubonic plague isn't a parasite. But if it is... did you see the 3/29 article in The Guardian where archaeologists and forensic scientists say "only an airborne infection could have spread so fast and killed so quickly"?

What do you think? Does this make more sense than transmission by rat fleas?

Jody writes:


Just a couple of corrections for when the discussion veered off into climatology.

La Niña is only the opposite case of El Niño and has nothing to do with the Atlantic. There are how ever oscillations in the ocean and atmosphere in the Atlantic as well, such as the North Atlantic Oscillation (NAO). It has been partly implicated in this cold winter in the US and the warm wet winter in Europe.

El Niño/La Niña also have nothing to do with undersea volcanos. At the most basic they are caused by changes in the trade winds affecting the depth and warmth of the upper layers of the Pacific. When the trade winds flow in one direction they expose cold currents (rich in nutrients) off the coast of South America and build up warmer water above Australia. The other way the warm water covers up the cold South American currents, cutting off the important marine food sources, and reducing the sea temps above Australia.

As a New Zealander I am very familiar with the Southern Oscillation Index which is one of the main measures of El Niño intensity. As a resident of Finland I am now learning of the effects of the NAO. Wikipedia as always has quite good descriptions of both and as well as other regional phenomenon.

And as a side note, I would say that human caused climate change is about as controversial among climate scientists as HIV causing AIDS is amongst virologists.

Thanks for the great podcasts. Even as a software developer I enjoy the whole TWiX series, although it is only TWiP that makes my skin crawl :-).


PS. Has Vincent thought of giving all the regular TWiX hosts the interview treatment like his recent podcast? I'm sure many are also interested in everyone else's backgrounds.

Scott writes:


As always I listened with considerable interest to your discussion of malaria, having had it many times. But when you got to the discussion of El Niño, that's where things went wrong.

El Niño is not the result of oceanic volcanism as you were speculating in the TWIP podcast of late March.

The El Niño and La Niña pattern is the result of the interaction of persistent trade wind patterns and surface water temperatures in the Pacific Ocean.

In normal years, the trade winds, which blow persistently from east to west, push surface waters in the Pacific towards the west. Current (last three hours) trade wind activity in the Pacific can be seen dramatically in this graphic:,-0.62,441

So ocean water that is pushed to the west by the trade winds, has to be replaced, and it is replaced by water rising from the depths along the west coast of South America. That water is extremely cold - and hence, the penguin populations in the Galapagos, which are located on the equator - the last place you'd expect to see penguins, and hence the chilly climate of Lima, on the tropical Peruvian coast. The penguins feed on herring and sardines, both cold water species, which flourish along the west coast of South America, in the upwelling cold water. The cold water generates little evaporation, hence the coastal deserts.

As the surface waters are pushed to the west, they accumulate around Indonesia/Malaysia, where they are pushed down into the depths. That deep, warm water is why that region is one of the most active thunderstorm regions in the world and the world's most active typhoon region - and, with global warming, becoming increasingly active.

On occasion, and for various reasons, the trade winds die down over a period of time, and the accumulated warm water in the western Pacific comes sloshing back to the east. Once it arrives in the eastern Pacific, the surface waters warm substantially, the sardine and herring fisheries die off, and the Peruvian fishermen starve. This usually happens around Christmastime, and hence, the Peruvians gave this phenomenon the name, "El Niño" referring to the Christ Child - in reference to Christmas. When this occurs, the warm water leads to increased precipitation, hence the flash floods in the Peruvian and Ecuadorian coastal deserts in El Niño years.

When the trade winds increase above normal, the pushback to the west is increased, and the opposite hydrologic effects occur. The cold water upwelling along the South American west coast is enhanced, and the herring/sardine fishery flourishes. This is a "La Niña."

Here in Costa Rica, our climate is dominated by the El Niño/La Niña cycle, so we watch it very closely (our worst drought on record by far was in the Great El Niño of 1984). So here is the current forecast for the "El Niño 3.4 index" for the next year, based on current climate models. A +0.5 or greater indicates an El Niño, and a -0.5 or greater indicates a La Niña. Close to the centerline has been dubbed "La Nada" The Nothing. The red line is the most watched model, the cyan line is the model consensus:

I hope this clears things up for you.

Regards from sunny and abnormally dry Costa Rica (77º as I write this),
Cartago, Costa Rica

Stacey writes:

Hi Vince and Dickson,

I came across this article on the IFLS website on facebook and thought it was really interesting. I do confess that I dont listen to TWIP as often as I listen to TWIV, but would love to hear your thoughts about this study (I promise to listen to the episode!). I can’t seem to download the article yet, apologies for only sending the link:

The weather here in sunny Pirbright is 16C and partly cloudy, quite a nice day in England lets be honest!

All the best,

Arbovirus Pathogenesis

Robin writes:

Homo sapiens is mostly an invasive species.

The species is adapted to life in tropical climates: any place that it needs clothes, it is an invasive species. Its natural migratory spread from Africa was through the (now) Middle East and South Asia to the Indonesian archipelago and thence to Australia. It did not need clothes for this.

Spencer Wells:
The Journey of Man PBS (playlist)

Everywhere else, it is an invasive species, needing clothing (and shelter) to survive. This includes the migration to the New World which passed through Beringia.

Gnathostomata are the "jaw-mouthed" vertebrates, as distinguished from the Agnatha, the jawless vertebrates (fish). The jaw is derived from the second branchial arch anlage. The clade includes the Sarcopterygia, the "flesh-finned" fish (with muscles in their fins) which in turn cladistically extends to the Tetrapoda: so, Gnathostomata 'R Us!

Thanks as usual for these most entertaining hours+. A whole lot more interesting because the subjects are intellectually stimulating. Dr. Dickson's resolve to stay at the tiller till the stars guide him elsewhere is much appreciated.


TWiP 70 letters

Robin writes:


While it is true that Taenia saginata tends to be benign as helminthic infestations go in humans, the same cannot be said for Taenia solium.

In both cases, ingestion of (encysted) larvae leads to enteric infestation with adult worms. In the case of Taenia saginata the eggs do not produce the encysted forms in human tissues.

Not so in the case of Taenia solium, where the eggs, even on vegetation, can be ingested by vegetarians, producing larval stages encysted in tissues, known as cysticercosis; an infestation in the brain, called neurocysticercosis, is particularly undesirable.

Segments of Taenia solium regurgitated from distal locations into the stomach can have their very numerous eggs all simultaneously activated by gastric juice, resulting in rather severe cysticercosis.

A species is an organism with a distinct group identity that can be maintaintained through multiple reproductive generations, even when hybridising across the entire group. Genetic drift limits species identity over time.

Jim writes:

Here's a link to an hour-plus podcast from EconTalk (!) by a journalist about the growing interest in exposure to pathogens to promote better immune responses. Looks like the related book has been out a year, and has only 54 reader reviews. It sounds like the interviewer, Russ Roberts, was reluctant to do the interview, but relinquished after prompts from several folk. I've not heard of the author or the book, but both may show up elsewhere, and the interview may provide enough insight to determine if the book is worth reading. Thought Dickson might be interested in listening and commenting on the concepts.


Smithfield, VA

Tim writes:

Hello Drs D and R!

I just listened to TWIP #66 where Vincent expressed his “I’m not mad, just disappointed” feelings towards the lack of emails received lately – so I’ll do my best. I would like to take the story of Schistosoma mansonii resistance to oxamniquine that you presented and appeal to Dickson’s ecologist side. It was found in the presented study that a single amino acid change inactivated the sulfotransferase activity of a Schistosoma mansonii enzyme, interfering with activation of the prodrug and conferring resistance. Assuming Schistosoma mansonii evolved the sulfotranferase enzyme for a reason, this inactivation must have come with some kind of trade-off. In the presence of the oxa drug, this trade-off is clearly beneficial. I am wondering if these resistant parasites are somehow at a disadvantage during the “normal” life cycle in the absence of drug since they are short an enzyme. Is anything known about this? Do you think that by removing the drug from the equation the parasites will eventually revert back to the active enzyme form by “fixing” the single amino acid change, thus restoring the enzyme function? Thanks for another great podcast!

- Tim

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!

Heather writes:

Dear Doctors R&D,

I'm catching up on old episodes and I very much enjoyed Dr. D's reading from his new book. I see that his vertical farm book is in audio format, will the new book also be available in audio format? Dr. D telling "stories" is one of my favorite parts of TWiP and I would love a whole book of them.

I also wanted to tell you how far-reaching your podcasts are. My husband works coordinating volunteers for a state park. A science club from a community college in Tennessee came to volunteer in the park during their spring break. My husband was very taken with how industrious and intelligent the group was. I work managing chemistry and microbiology labs for undergraduates at a state college, so I was naturally slightly suspicious of these assertions. The students and their advisor invited us to have dinner with them and I must admit I found them very engaging young people. Due to my interests and previous work with parasites and microbiology the conversation naturally turned in that direction. One of the young ladies, who couldn't have been more than 18 years old, mentioned that she absolutely LOVED all the TWiP, TWiV, and TWiM podcasts and is pursuing microbiology as a field with an interest in cyanobacteria. I thought you would enjoy hearing how your work inspires some of the youngest of the new generation of scientists. Thank you for the excellent podcast. I look forward to more "stories" and I really like having guests like Sagi on TWiP.

Peter writes:

Dear Dickson and Vincent.
I saw this paper and thought that it could be discussed on TWiP:

Interview with lead author of the study Rebecca A. Cole, PhD, Parasitologist with the US Geological Survey’s National Wildlife Health Center

Fiona writes:

Dear Vincent and worm enthusiasts. I have been listening to your podcasts for a few years now. I have personally seen and have pictures to prove that there is new species that is infecting millions. Myself included. I copied the following url and am interested to know what you think about the following? This is prolly TMI but to get these things out of me I have been administering MMS enemas and every single time I do these rope worms come out of me. WTF. I love your how you are both very witty and your worm info is awesome.
HELP. Fiona

Angelica writes:

Hi, my name is Angelica. I have a question regarding Lamblia intestinalis. How long antibodies are produced in blood against lamblia if infection occurred? Can we detect infection by blood test even if it is chronic infection? I will be very grateful for answer by email
Kind regards,

Paul writes:

Hi, I recently listened to your podcast on Giardia and have a question about treatment and life cycles that I can't seem to find anywhere in research papers I have read on the subject.

I understand the 2 stage life cycle of this parasite and that antibiotics will kill it during the trophozite stage, but what about the cysts? Do they survive the antibiotics and therefore will just develop and reinfect once you've finished the treatment?

Consensus seems to be that it is a pretty difficult infection to get rid of, is this the reason why? It would seem to make sense to me to do a second round of antibiotics to kill all the Protozoa that were in the cyst stage during the first round, but I can't find any mention of this in the literature or anything on the life-span/timing of the life-cycle to know when to administer a second dose to ensure complete eradication?

I found your podcast to be very helpful in understanding this parasite and thought you might have the answer to my questions?

Many thanks,


Dave writes:

Those who get precise about ice ages say it something like this: "The last three million (I'm guessing) years have been an 'Ice Age'. During this ice age, there have been several discrete glaciations."

The height of the most recent glaciation was ca. twenty thousand years ago. It tapered off for a few thousand years before entering the (recently ) current interglacial.

Keybrd gone back.



Dave writes:

El Niño is the Boy Child (Jesus). It is the warm anomaly in the Pacific. La Niña is a girl child, named for contrast, and is a cooling period in the area of the Pacific anomaly.

I don't know squat about the identification or naming of the anomalies in the Atlantic, but I wish I did. If somebody put La Nina in the Atlantic, it's news to me.

PS The Cali drought is the worst on record, beyond past dry periods associated with Niños. It is unknown if it will resolve, repeat, or persist for decades. The decline of glaciers in the Sierra (over past decades) may interact with decreased snow pack. In any case, a dry year means a decreased snow pack, the melting of which has been the primary source of water for ag and people in Central Cali. 0% of water contracts is going to most farmers this year. It is a big big deal.

Love, dave

TWiP 69 letters

Richard writes:

Hi Vincent and Dickson,

I enjoy TWIP, and often recommend it to my students. I'm a parasitologist, primarily a Leishmaniac, but I have learnt a lot from TWIP. I find it both more educational and entertaining than Car Talk.

The discussion on TWIP67 about nitrile drugs for Chagas disease was excellent, but I wanted to point out a common misconception about the amastigote, which does in fact have a flagellum. It is a non-motile, intracellular stage, but it retains a short flagellum, which is clearly visible in electron micrographs. The same is true for the Leishmania amastigote.

The flagellum, in all stages of these trypanosomatid parasites, arises from a structure called the basal body and emerges from the cell body in a specialised region of the cell surface called the flagellar pocket. The flagellar pocket is an invagination of the surface membrane which appears to be the only site of endo-and exocytosis in trypanosomatids. While in motile forms (promastigotes, epimastigotes or trypomastigotes) the flagellum extends for some distance outside the cell and gives the cell motility, in amastigotes it does not emerge from the flagellar pocket. However, while the non-emergent flagellum cannot confer motility, this does not mean it has no function. One possibility is that the flagellum is a sensory organelle, reporting on the environment of the parasite. In fact, the trypanosomatid flagellum is structurally and evolutionarily related to organelles that are responsible for sensing in vertebrates - olfactory sensors in our nose are a good example.

We have shown that motile stages of these parasites can respond to chemical stimuli in the environment, by swimming towards or away from them. Amastigotes can't swim, but it may still be important for them to sense changes in their environment.
Maybe we could compromise amastigotes by perturbing their sensory apparatus?

One other point. You cited Plasmodium as an example of a protozoa that does not have a flagellum. In fact, the male gametocyte undergoes a striking process called exflagellation to produce motile, flagellated gametes in the mosquito gut. This is the only flagellate form in the complex plasmodium life cycle - there are more exceptions than rules in biology.

Thanks so much for doing a great job with TWIP.

All the best

Institute of Infection, Immunity and Inflammation
Glasgow Polyomics
College of Medical, Veterinary & Life Sciences
University of Glasgow

Hilary writes:

Hi there, professors Despommier and Racaniello!

I'm a final year student doctor from sunny Melbourne (today: 24 degrees Celsius, sunny, with a 15km/h southeasterly) just writing to let you know how much of an inspiration your podcasts have been! I have always had a passion for parasitology, ever since my undergraduate microbiology days - not to mention an unfortunate encounter with the 1998 Sydney giardia outbreak. The entertaining, insightful and always educational content of your TWIP podcasts has kept me inspired and engaged through many long commutes. I count you guys amongst my greatest insipirations and must confess I have named two of my favorite zebrafish after you ( along with other luminaries such as Freddie mercury and sir Ed Hilary, as well as some very inspiring pharmacology professors). Nothing more to add, just keep up the amazing work,


Pete writes:


Hi professor guys, emeritus or otherwise!

I have been listening to the trio for a couple of years now, ever since you were on Sceptics Guide. Recently, for some unknown reason, I downloaded the early TWIP episodes.

So, to the question: about 6 months ago I had a holiday in Laos: probably the best I have ever had.

I was in the country-side one day, at a village home stay, when my host invited me to a celebratory lunch at a small local school. I ate some (well cooked, and delicious pork), but eschewed the dish based on blood, which I am glad they warned me about.

After many rice wines and a few local beers, we retired to the guest of honour's home. Where we ate and drank even more. One of the dishes was produced from a banana leaf, and I had a nibble. Whereupon someone informed me it was cured pork, with spices. It was delicious. But I do distinctly remember saying "that is not good falang [foreigner] food".

So, to a couple of questions:

1. Could there have been Trichinella in the blood based dish? I have no idea how much it was cooked.

2. How many organisms could I have possibly ingested in a few grams of cured pork?

3. Could I have developed an immune response from that that will benefit me in later years?

Thanks you guys,

Josh writes:

Drs. Despommier and Racaniello.

Thank you so much for the show! I think I speak for many listeners when I say that both of you have had a profound personal affect on my life through your (mostly) weekly teaching. TWIP was the major inspiration behind my decision to leave a career in woodworking and cabinetmaking to pursue a degree in biochemistry (which is off to a great start, by the way).

Onto my picks: I've been meaning to pick this first one for a while. I came across the blog of Nathan Shields when it was feature in a brief by the New York Times. He's a math teacher who started making fun pancakes for his kids.

I thought they were hilarious, so I scrolled through and hit the weekly pick jackpot:

A TWIP listener, maybe? My other pick is The Winged Scourge, a Disney propoganda film about the spread of malaria featuring the Seven Dwarves. It was apparently created for the Coordinator of Inter-American Affairs in 1943 for a Latin-american audience. The eradication methods seem a bit dated, but it's pretty educational and very entertaining!

Thanks again, gentlemen!

John writes:

Dear Professors,

You requested more reader email, so here is more reader email.

It is below freezing outside and I have a bandage on my finger.

I am writing again to share a paper about squirrel parasites. Again, there is more than enough here to fill an episode.

Franklin's Ground Squirrel, Spermophilus franklinii, lives in the northern prairie. Unlike the gray squirrel that bit my finger by accident, these squirrels often eat meat, catching prey as large as hares and mallards.[1]

As omnivores they have more parasites than their herbivorous cousins. Here is a parasite inventory from a paper.[2] I only recognize one
genus name from TWiP. I hope a parasitologist on your show can discuss life cycle or habits of some of the others.

Apicomplexa: "Eimeria bilamellata, E. callospermophili, and E. spermophili."

The last two species names are derived from genus names of ground squirrels. Do they only infect ground squirrels?

Cestodes: "Hymenolepis citelli was the most common cestode, Choanotaenia spermophili and Taenia mustelae were found in the liver,
and larval T. taxidiensis was found in distal muscles in the rear leg."

I do not recognize the first two genera. Taenia is the genus including common human-infecting tapeworms. The Latin names translate
as "weasel tapeworm" and "badger tapeworm." I assume squirrels are among the intermediate hosts.

Trematodes: "The trematode Alaria mustelae was found in lungs of 6 S. franklinii and in the spleen of 2 individuals. Plagiorchis proximus,
also a trematode, was found in the small intestine of 1 individual."

I found a list of hosts and stages of Alaria mustelae in another paper: "A snail which harbors the sporocysts producing cercariae, a
tadpole or frog into which the cercariae penetrate and in which they become immature metacercariae or agamodistomes, here to be called
mesocercariae, a mammal (mouse, mink, or raccoon) which carries the metacercariae, and another mammal (mink or weasel) the host of the hermaphroditic adult." [3]

I would have designed a simpler life cycle, but nobody asked me.

Nematodes: "The most common mature nematode, Physaloptera spinicauda, was found in the stomachs of 13 individuals. Spirura infundibulifomis was found in the stomach and esophagus. Capillaria cf. hepatica was found in the liver, and Citellinema bifurcatum occurred in 3 individuals."

I do not recognize any of these genera from human-centric TWiP.


[1] Sowls, Lyle K. 1948. The Franklin Ground Squirrel, Citellus franklinii (Sabine), and Its Relationship to Nesting Ducks. Journal
of Mammalogy 29(2):113-137 (

[2] Ostroff, Andrea C. and Elmer J. Finck. 2003. Mammalian Species, No. 724, Spermophilus franklinii

[3] Bosma, Nelly J. 1934. The Life History of the Trematode Alaria mustelae, Bosma, 1931. Transactions of the American Microscopical
Society 53(2):116-153 (

Sorry, only the second is open access.

Art form photographics writes:

Thank you for your wonderful episode on parasitology #67

David writes:

Vince and Dick,

Really glad I found your TWIP podcast. I have started on episode 1 and am working my way up so I am not at the current episode yet. The information you provide has been a great help in my invertebrate zoology course. I have been able to bring a lot of additional information on the parasites we study in the course due to TWIP. Keep up the great work.


David W. Allard, PhD
Professor of Biology
Texas A&M University-Texarkana

Jim writes:


I wrote TWIV last week about but now have reviewed the 140 projects shown and see four are related to parasites (lung fluke, mosquitoes, parasitic zombies, worm cures) in case this approach interests your listeners. If you support a project, you gain access to progress reports, but after the deadline you can't contribute to gain this access. Something for fence-sitters to keep in mind. I contributed to one project, but it may not reach its goal in which case the contribution is returned and I can use it again, elsewhere. I was a little concerned, at first, about the qualifications of the researchers and couldn't find any details, but now see the site provides background on each project. Also, the site has been around for several years, starting out with the name "microryza" which might be of interest to Prof Schachter.


Smithfield, VA

Suzanne writes:

I write too much :) The issue with people being anti-evolution has less to do with a specific religion than with the rise of fundamentalism. Plenty of Christians don't believe the Bible is factual in the same way scientific evidence is. It's just the ones who do who want to try to squeeze creationism into science.

I believe the main fight against Darwin's theory of evolution began a century or so ago as a reaction to so called social Darwinism at a time when eugenics was a somewhat popular idea. I sat through a sermon not too long ago at my parents' church by a preacher who assumed altruism had no place in evolution. I really wanted to stand up and correct him but figured my parents wouldn't forgive me. It's really frustrating down here in Texas where evolution hasn't been taught in a lot of schools for generations to the point that some people don't even understand what they're trying to keep their kids from learning. And really it's just a noisy minority causing the problem. A lot of people who go along with the creationists or just don't think about it enough to care aren't even really creationists. If you mention natural selection they don't bat an eye. They understand that the flu can mutate. It's just the word evolution that conjures thoughts of monkeys and leaving the poor to die or something.

TWiP 68 letters

Tim writes:

I listened to the latest TWIP this morning. Dickson mentioned the herbicide atrazine but thought it was a fungicide. It is actually a herbicide in the photosynthesis inhibitor class. Another bit of trivia about ag chemicals is that old chemicals like atrazine are making a big comeback in usage due to resistance problems emerging in fields. Too many farmers were spraying nothing but glyphosate on fields due to that being the first GM herbicide resistance trait and now weeds have caught up.

On the subject of monarchs having a bad taste so birds leave them alone you seemed dubious of bird memory and the difference one birds experience meant for monarchs on the whole. I think the reason it works out well as defense for monarchs is that the generation interval for insects is much quicker than birds and some birds live quite long lives and would most likely experience the taste of monarch early in life and not forget because they are not only bad tasting but I believe poisonous due to milkweed that they feed on as larvae. I've tasted milkweed and if monarchs taste like that I can see why birds would avoid them.

I found it interesting you have the view of humans as separate from the general ecology of the earth. Full disclosure: I wrote a paper comparing humans to weeds and pathogenic bacteria in college but have since changed my mind on that subject. I've been working on changing people's minds about that on social media because it seems once we view ourselves as separate from the rest of the world we live in it seems to give people license to do things that make no sense from an ecological sustainability standpoint. To put another way stealing a term from economics, theres a risk of moral hazard when one divorces themselves from their surroundings. I'm not saying this to criticize your thoughts on it and I'm sure you have a much more nuanced full view of the subject. Just some thoughts of mine on that topic.

Scott writes:

Hi Vincent and Dickson!

I just finished with ep64 and wanted to drop you guys a note to hopefully fill up your inbox since you only had 4 emails. I am a Hydrogeologist working for an environmental consulting company in Cincinnati OH, which is currently overcast 24F, 79% humidity, winds at 8 mph out of the S/SE. Though hydrogeology has almost nothing to do with biology i love listening to TWIP, TWIV and TWIM while doing my mundane data manipulation and am a lover of anything science. The furthest we tend to dive into biology would be the injection into groundwater of Dehalococcoides for the sequential reductive dechlorination through the daughter products cis-dichloroethene and vinyl chloride to ethene (guess its a little more relevant to TWiM than TWiP). Please keep going off topic! I love hearing the banter back and forth between you guys! Anyway i love the podcast and look forward to every episode. Hopefully, there are many more to come!

John writes:

Hello TWIP!
I just finished listening to episode #67 in which Vincent asks, "Why was a priest doing experiments?"

I'm parasitologist who will be ordained a priest this June and will teach biology at Creighton University. I earned my PhD in evolutionary biology from OSU before entering the Society of Jesus (AKA Jesuits) in 2003. After ten years of studying philosophy and theology, teaching biology and doing research, I could probably devote an entire TWIP podcast to the topics of priests "doing experiments" as well as parasitology and religion, but let me briefly state the following:

Christianity helped develop science because it assumes (unlike some Eastern philosophies) that the world is real and not an illusion.

Christianity also assumes that the world of creation remains distinct from the world of the supernatural Divine. So unlike many pagan religions that believe in nature gods, Christians assume that Nature follows laws that can be studied.

Finally, Christians believe that God created the world good. Thus, Creation reflects the Creator and so learning about Nature teaches us something about God. In other words, investigating the world of nature and is worth doing.

You (and your listeners) can check out some of my on-line articles on this and related topics at The Jesuit Post,

Thanks for the great podcasts and keep up the good work. I plan to use some of these podcasts when teaching parasitology.


Alex writes:

Hi Both Vincent and Dick,

Love the podcasts, in every way but for one thing. Vincent is very clear to hear, Dick fades in an out - meaning a volume can never be perfectly set. I thought I'd illustrate as below ;)


Please fix this so I can continue to enjoy stories from the world of Parasitism....



Christophe writes:

Hi Vincent,

Just thought i would pass on this link incase you had not heard about it already.
I have not watched this documentary series yet but i think i will try and track it down. I heard about it on the BBC Science hour podcast today and would like to hear Dickson and your thoughts on it.

ps. I love the TWip/TwiV/TWiM podcasts - i am only a high school graduate and self taught web designer but find all the TWiP/V/M fascinating - keep up the great work.

"Swallowing three cysts which are twitching with tapeworm larvae sounds like the stuff of nightmares.
But for the past two months, BBC presenter Michael Mosley has been taking part in a toe-curling experiment, allowing three worms to live and grow in his gut.

As part of BBC Four’s natural world season Dr Mosley infested himself with some of the world’s most prevalent parasites including leeches, lice and mosquitoes."


Robin writes:

Marianne writes:

Dear Drs. Racaniello and Despommier;

I do enjoy your podcast, as I do all the TWiX. I've written to TWiV previously, but this is my first opportunity to email TWiP. Your request for emails in the last episode sealed the deal.

I couple of episodes ago you bemoaned the lack of ecological based parasitism research. I smiled to myself because my first undergraduate research experience was in this field. I was a summer student on a field project trapping the prey species of the pine marten of Newfoundland ( and studying their parasites. I learned a lot that summer, including that I was not cut out for field work. Two months in a cabin on the east coast of Newfoundland was enough for me. I happily started my career in the lab studying immunology, virology, cancer and now vaccines.

More recently, I've been thinking more about parasites, due to my increased interaction with rescued cats. After losing two older cats, we decided to adopt a kitten from a local rescue that helps trap, spay/neuter and then adopt or release feral cats. Before we could adopt our chosen kitty, he had to clear a pretty significant coccidia infection. Of course, through my renewed interest in the subject through listening to TWiP, I was interested in what type of infection our little Felix had, but learned that most vets only look for the presences of oocytes in the stool and since the treatment is basically the same for all coccidia, they don't differentiate. We then fostered a stray mother cat who gave birth to 5 kittens about 12 hours after we brought her inside. Those kitties were happy and healthy until 2 of them went to a local pet store who helped out with adoptions. They both became quite ill with coccidia, while the two we kept in our house remained healthy. I suspect that the well meaning pet store was unwittingly spreading some of these pesky parasites to young kittens through previous inhabitants. Luckily, after several antibiotic courses, all are happy and healthy in their adoptive homes.

On a related note, just last week I saw this story, regarding Toxoplasma gondii cropping up in a beluga whale in the Beaufort Sea.

The story also mentions that Sarcocystis pinnipedi may be responsible for a large die off of grey seals off Cape Breton in 2012. They are suggesting that the parasites are being released by ice thaw. What do you think?

Oh as for the obligatory weather report, its a balmy 4oC here in Halifax, Nova Scotia, Canada. However we are expecting a mix of rain, freezing rain and snow overnight and they are anticipating the temperature to dip to -7oC (wind chill of -14oC) by morning! Still a bit of winter left here in Canada!


Oskar writes:

Hello TWiPers!

I'm studying the third and final year of the Biomedical scientist programme at the Gothenburg university, Sweden. I've just spent my work studies at a medical parasitology lab where I introduced the "old timers" to TWiP. Naturally they became hooked immidiately. Listening to you guys really made it easy and fun to learn the theoretical part of working in a parasitology lab, so I just wanted to say thank you!


PS. The temperature here is a chilly 3 degrees C with rain.

TWiP 67 letters

CN writes:

Greetings Profs,

After having listened to your discussions on Plasmodium (TWiP 64), I explored papers on treatment options that are actually available. After having read some papers, I realized that one of the main roadblocks are the hypnozoites. If I have got it right, apart from the fact that it is involved in reactivation of infection, it's dormant nature allows it to evade the antibiotics. My first thought was "Can the hypnozoites activate the immune system, and can it be a vaccine target." Your thoughts on this would be very helpful.

In connection with the search, I found a paper in nature, cited below which i find is a worthwhile discussion topic on malaria.

Host-cell sensors for Plasmodium activate innate immunity against liver-stage infection

Thank you for all the time spent on educating us

TWiX fan

Kim writes:

Hi Vincent and Dickson,

I just want to let you know that I would very much like to attend a Coursera course on ecology lead by Dickson! I really enjoy episodes such as TWiP 65, where ecology, parasitism and various infectious diseases are intertwined and would love to learn more about the ecological aspects. However, as I study purely infectionbiology I don't have the mental strength to start studying ecology on my free time, as I feel it is hard to know from where to start. Here, I think, a web-based course would be a great way for me to learn more and would keep my interests up with Dickson spicing up the potential future lectures with references to both parasitism and vertical farming! I really hope this materializes.

best regards,
Uppsala, Sweden
-7 Celsius

TWiP 66 letters


Andre writes:

Dear Vincent,

To my great delight, I just discovered your podcasts twiv, twim and twip.

The first twip I heard, about Strongyloides stercoralis, although informative and interesting, seemed to have several inaccuracies. I was not able to find the email from Dick Despommier, and therefore I am writing to you.

Dick said that Strongyloides, when it enters into the host, becomes a protrandrous hermaphrodite adult. Actually this is not true. The parasitic stage of Strongyloides is a female that reproduces by parthenogenesis.

He also said that a protrandrous nematode is first male and then becomes female, so that it can self-fertilize. Actually, as I said, Strongyloides is not a hermaphrodite and therefore it cannot be protrandrous. The only nematode parasites that I know to be a protrandrous hermaphrodites are worms of the genus Rhabdias, which usually infect amphibians and reptiles.

C. elegans is a good example for a protrandrous hermaphrodite nematode. The term protrandrous means that the organism first produces male gametes and later shifts to the production of female gametes. The only difference between C. elegans hermaphrodites and females of closely related species is the ability of the hermaphrodites to produce a limited amount of sperm just before becoming adult. These "female-bodied C. elegans with sperm" are not considered males because they cannot transfer their sperm to other individuals. The sperm of these worms are stored in the spermatheca and used for self-fertilizing the oocytes produced during adulthood. C. elegans males are morphologically very different from hermaphrodites, produce only sperm, and have specialized mating structures used to find and fertilize the hermaphrodites.

My field of specialization is actually evolution of modes of reproduction of nematodes. I study a free-living nematode that can produce males, females and hermaphrodites. In many ways, it resembles parasitic nematodes, because larvae that sense the lack of food become "dauers", which is the dispersive stage of free-living nematodes. Dauers are the equivalent larval stage as the infective stage in parasites. Dauers can resist to harsh environmental conditions, crawl in arthropods and be transported to new places. For the species of nematode that I study, the dauers develop into self-reproducing adults once they encounter a habitat with food. This makes sense, because they can then colonize new environments without the need of a mating partner. The larvae that grow in an environment with enough food develop into females and males.

In case you are interested in reading more about it, check the paper Chaudhuri et al in the website



Noah writes:

Dear Prof. Racaniello,
I have been a huge Twiv, Twip, and twim listener for about a year, I love the show.. Twip the most.. I love listening to you and that Deponia guy.. you guys make me laugh but more importantly I have attained a great deal of knowledge from the podcasts can't help but tell my collieges about the amazing things you two talk about from Toxoplasmosis or several parasite epidemics.

I am writing you b/c tommorow night I am going to post you as The American of the Day in my facebook group because of your great
accomplishments and devotion to educate the public about science. If you get time on the 10/23/13 search the Facebook group American of the Day and you will see your photo and bio added to our list of great Americans... it's a small and I have a feeling you won't have time but thankyou so much for the podcasts there is nothing like it out there, if it wasn't for you guys I would have to read these journals all by myself and that gets both confusing and lonely. Thanks again-

Noah RN --- Lebanon PA

Devin writes:

Hey guys:

I am from the San Francisco Bay Area and I wanted to extend my appreciation for the show! I listen to both TWIP and TWIV and would be disappointed if you didn't produce the show into the future. The conversations require the listener to pay attention a bit more than the average podcast, I believe. This may, in part, be due to the use of terminology that I often find myself looking up during the podcast or later when I've heard it more than once on the show. As a result I feel like I'm in on a conversation that I normally wouldn't be and this inspires me to try even harder to understand the concepts.

One more thing: While out at a bar the other day I had randomly met someone who had his Phd in the biosciences (I don't remember specifics -- I studied Earth & Planetary Science) and I had mentioned that I listen to TWIV and TWIP and he knew who Vincent was, which led to him to add your podcast to his iTunes at the bar.

Keep up the good work. I looked for your podcast page on Facebook and didn't find it -- did I miss something? If not, you should create one. Its a good way to promote your show.

Remember for every person that writes an email there's probably a bunch more that want to but just don't get to it.

Thanks guys!

John writes:

Dear Professors,

It is 1 degree outside my window as I write three comments about TWiP 63.

1. You wondered how Plasmodium DNA ended up in ape feces. I learned biology when life was made of cells rather than molecules, so I think of the body not as a big amino acid sequence but rather as a series of tubes. With this old-fashioned background, I thought the path dismissed by Dickson was obvious.

The liver recycles old red blood cells to recover iron. It dumps the rest of the cell contents into the intestines. If it recycles an
infected red blood cell, the waste may include Plasmodium DNA.

2. How do merozoites know when to stop producing copies of themselves and make gametocytes instead? I can imagine three mechanisms:

(a) random chance

(b) a molecular clock like telomeres, which allow cells to count generations

(c) environmental cues related to overpopulation, such as oxygen concentration

If you give me a grant and a lab I would be happy to watch a team of grad students investigate.

3. Do I understand correctly that a deadly infection can result from just one Plasmodium sporozoite cell lodging in the liver? (15 minutes in)

Scott writes:


As a resident of Latin America, it was with some interest that I noted this story in Science Daily. I would appreciate your comments:

As I have, on several occasions, discovered the insect vector in my living space, this parasite is of some concern to me.

I would like to know if the parasite is a threat to the two cats who live in the house with me, or my dog who lives in my yard. I have not been able to find any information on the veterinary implications of this parasite.

Regards and thanks for a great podcast,
Cartago, Costa Rica

Neva writes:

Hi Dickson and Vincent,

I guess the tri-caster medical device is almost here. If this is viable, very cool! What's next?

Rice University researchers have developed a noninvasive technology that accurately detects low levels of malaria infection through the skin in seconds with a laser scanner. The "vapor nanobubble" technology requires no dyes or diagnostic chemicals, and there is no need to draw blood.

Never miss your great podcasts!

Neva from Buda

J writes:

I got recommended your podcast from a colleague. I just wanted to know what song by RJ do you play in your intro? I emailed him and he thought it was "Guitar Sounds" but it's not quite right. Do you mind posting the title somewhere ?



TWiP 65 letters


Perry writes:

Greetings Vincent and Dick,

Hooray for finally mentioning G. pulchrum in episode 62, my most favorite parasite and one worthy of further discussion. As a diagnostic veterinary pathologist, I encounter this spirurid in approximately one third of the dairy cows I autopsy. It is much more common than you surmised. I make a big deal out of its frequent occurrence, not because of its pathogenicity (essentially none), but because it is a paradigm organism. It insinuates itself in the esophageal mucosa, wriggling back and forth in the epithelial layer as it advances (that is why it is called the 'ribbon candy' worm) thereby maintaining its hold and evading immune surveillance. The paradigm is that it is a beautiful example of an innocuous host parasite realtionship and the fact that most diagnosticians readily overlook it. Students of pathology all too often 'look' but fail to 'observe'. A south african veterinary pathologist told me that Gongylonemiasis occurs in the mouth of poor ruaral children, presumably due to the ease with which they ingest an infected beetle intermediate. It has been some time since I last reviewed the literature, but I believe the nematode is world-wide and capable of parasitizing innumerable mammalian species. I enjoy your program, biomedical science musings and digressions. Keep up the good work.

Curt writes:

Hello, Vincent and Dickson!

First, let me start with some praise. I thoroughly enjoy all of the TWiXcasts, but I appreciate TWiP in particular for its one-on-one format and the wealth of clinical experience and case studies that Dickson brings to bear in every episode. I finished Vincent's outstanding Coursera course recently- looking forward to part two, on that note- and it set me to wondering when Dickson is planning on doing a Coursera class on parasitism.

I'm writing because I'm curious if the military has ever tried to weaponize helminths. I'm aware of past efforts by the military to weaponize practically everything, especially in the realm of pathogens- running the spectrum from from Y. Pestis and Smallpox to Coccidiodes fungi. I wouldn't imagine that an attempt to weaponize helminths would be very successful, though, and attempts to imagine such a program are baffling at best.

Keep up the outstanding work, gentlemen, and thanks again for your time and effort.

Cathy writes:

Dear Professors Despommier and Racaniello,

I wanted to write to you to thank you for taking the time to do these fantastic podcasts. TWiP was recommended to me by a former colleague with whom I worked in Professor Paul Duprex's virology lab at Queen's University Belfast, before he moved to Boston University. Since working with Prof. Duprex I got my PhD in molecular parasitology, and now I work in St. George's University of London on the nanomal project (the link for which I've included) which you may find interesting:

We're developing a hand-held point-of-care diagnostic device for malaria that can give a diagnosis in under 20 minutes, but the really exciting part is it will be able to speciate and detect drug resistance-conferring mutations so an informed treatment choice can be made.

Being a malariologist I particularly enjoyed TWiP#35 with David Fidock, and my interest was especially piqued when the contentious subject of artemisinins' mode of action was brought up. I thought this was about to be explored but alas, it was not. Of course, there are not enough hours in the day to debate that subject. If you are interested, however, we recently published an opinion article in Trends in Pharmacological Sciences on the subject which I have attached. Professor Fidock mentioned the haem hypothesis, but I am more in favour of the SERCA hypothesis, which postulates that artemisinins specifically inhibit the sarco/endoplasmic reticulum calcium ATPase (SERCA) of the plasmodia parasites. People may feel that knowing the mode of action of a drug is purely academic, but as you are well aware drug resistance is a serious problem for controlling malaria, and knowing how a drug works can help identify any mutations responsible and hopefully overcome resistance.

Thank you again for all the time and effort you put in to these podcasts. I have thoroughly enjoyed learning about different parasites, not to mention american history and piscatorial pursuits, and constantly recommend TWiP to my fellow parasitologists. I plan to start listening to TWiV but it's been quite a while since my virology days. I hope I can keep up!

Yours sincerely,

Lisa writes:

Hello to Vincent and Dickson, TWIP

First may I say, that it's great you are putting such in-depth content out in the public domain, People such as yourselves, with vast amounts of knowledge and years of experiences giving your knowledge freely is fantastic and I apualde your for it. And not to mention your presentation style is superb and funny.

The Microbe world fascinating to me, I bought a decent Amscope microscope last year, I have always wanted one but after getting into TWIV /TWIP /TWIM, I finally bought one. I've used it many times looking at pond life/mouth bactria/poo from my dog "Bella" who is female and very coprophagic towards next doors cat :( I basically put anything i dare put on a slide to the horror of my fella, Our daughter loves it too, with all the "yucks" and "Errrs".

Anyway to cut a long story short, Not that I have been waiting for a decent infection but last week I contracted what I thought could only be described as food poisoning, after 24 hours of (diarrhea/vomiting/burping/feeling bloated/major cramps) I thought the best thing to to is check a stool sample, naturally..... As I had never been so ill
My thoughts were that it could be Food poisoning but i wasn't convinced, after going back and hearing TWIP #16 Giardia Lamblia it rang a few bells.

On investigation all could see no Giardia Cysts but I could see many uniform tubes with constrictions at the end, Being uniform and tube like my first thought was Dog Tapeworms? Or could it just simply be something I ate as it looks like plant matter, I'm sure if it is parasite debris then Dickson can identify it in a jiffy.

After searching Google to no avail, I feel I may need a copy of "People, Parasites, and Plowshares" for future use?

Here are a few pictures of the tube like forms? Seeing as though Dickson has seen many stool samples in his time, I thought it to be great opportunity to write in and express my gratitude for all the great work you are doing plus a token of that appreciation.

Keep up the good work and thank you so much for bringing science to the rabble.


TWiP 64 letters

Richard writes:

Good morning, day, evening (depending on your time of day). Esteemed professors!

Firstly my weather report, for Weston super Mare, uk.

It is currently 3 centigrade (feels like 2C), dew point 4C, humidity 78%, there has been 1mm of rain/sleet, with a 50% chance of further precipitation, and the wind is 16 km/h from the WNW. It is currently dark so no visibility, but this is estimated as 2 miles, as it is cloudy with light rain.

The predicted high for the day (2PM) 9C, with humidity of 68%, and dew point of 4C, with predicted wind of 21km/h, a 40% chance of precipitation (rain or sleet), to is expected to be partly sunny, with good visibility >10 miles predicted.

I hope the weather report meets your increasingly exacting requirements :)

My question is actually fairly simple; Giardia lamblia and a number of other eukaryotes lack mitochondria. Most of them appear to be anaerobic, and I can see the point that the mitochondria and electron transport mechanism might well be selected against.

However, no where can I find if it is clear that mitochondria where selected against, and lost. Or if these bugs are a branch, that where started before eukaryotes adopted mitochondria.

I'm not scientist, but simply an interested party. I actually work as an engineer, on sewage treatment plants. So I do get to see a lot of bacteria, since they do all the work, treating the sewage. Given plenty of oxygen, and the correct nutrients, they do a fine job of this, and then happily settle out, leaving clean enough water that it can be returned to the environment (or with minimal treatment, and filtration, to the drinking water supply, as is becoming more popular).

However it is my personal theory, that apoptosis in eukariotic cells derives from the incorporation of a once parasitic bacterium. Such a parasite requiring a method to kill the host cell, in order to proliferate into the medium, to infect other cells. I hypothesise that this was co-opted by eukaryotes, in order to allow for apoptosis (or programmed cell death).

Knowing if apoptosis odours in eukaryotes, that lack mitochondria, and if they are a pre mitochondria branch, would answer my question. However I have been unable to find the required information.

I wonder if you can point me in the right direction, and also thought the subject might lead to an interesting conversation on the podcast.

Many thanks for your ongoing series of podcasts.

I have emailed this to both TWIP, and TWIM. I suspect it is better suited to TWIM, but my research has been on parasites, since these seem better studied, so have included TWIP.

Thanks in advance for any insights you may be able to provide, or simply interesting conversation.



Dave writes:


Hiya! Entering mid-dialogue, so sorry for out-of-touch points hereafter. Trivial anyhow.

As to fuel powered machines and discovery of oil deposits (identified as refineable fuel, since deposits were mined for minor purposes in antiquity), um, as I recall, Henry Ford intended his internal combustion engines to run on ethanol at the outset. I have no idea how far earlier the engine-makers planned ethanol, but.... Anyway, Rockefeller et al came along shortly to amend all that. Besides, obviously y'all were perfectly accurate about all that machinery thing and slavery.

More to the point of parasitology, another trivial emendation may be that the first hookworms didn't necessarily enter N. America on African feet after 1600. West Africans had been transported to Caribbean islands for labor by mid 1500s. They may have inoculated soil there with hookworms, which may have been picked up by sojourning barefoot non-Africans, and transported to N. America first by those people after 1600. Maybe. (If I haven't misremembered the true mid-century. Got it from "Diary of an Irish Slave Girl," a novel about a kidnapped child who was taken to a British sugar plantation and ended up marrying an Ashanti man. Therefore my historiography may be off. But I do think those island plantations were started up in the 1550s or so -- and, from other sources, European population growth began to explode, apparently correlated with sudden availability of enough extra calories to delay starvation, preserving more children, etc.)

So anyway. Hope It's not wasted your time. Entertained me, but not enough to edit it down.


Benedict writes:

I love your show, I hear it on the way to work and home again each day. Would love to hear during work as well but my coworkers would complain I guess. I have a question regarding the theme song at the beginning of twip63. What song/remix is that?
Kind regards and all the best!

John writes:

Dear Professors,

I have listened to you discuss parasitic diseases in mice, fish, mosquitoes, ladybugs, cats, and even humans, and feel you have paid relatively little attention to squirrels. A recent paper in BMC Veterinary Research could help cure that deficiency.

British veterinarians studied 163 dead red squirrels. The squirrels were mostly found near houses and roads, and half of them were killed by cars or pets.

The dead squirrels were examined to determine cause of death and inventory parasites and other disease causing agents.

I spotted at least four eukaryotic parasites -- three Apicomplexa and a nematode -- only one of which I recall hearing about on TWiP.

Toxoplasmosis was blamed for one sixth of squirrel deaths on the Isle of Wight. It was considered a direct cause of death rather than a contributing factor like when it prevents mice from avoiding cats.

Hepatozoon infections were common in lungs and heart muscles, and Eimeria in gut contents, but neither seemed to be a primary cause of poor health.

The last parasite is so obscure it does not even have a Wikipedia page. It is related to pinworm, which you have discussed. Quoting the paper:

"Nematodes were sometimes observed during gross and histological examination of intestine. Morphologically they resembled pin worms (Enterobius sp.) but, apart from one case where they were identified as Rodentoxyuris sciuri, none were submitted for species identification. Typically there was no apparent associated pathology but one juvenile with a heavy nematode infection died due to an intestinal intussusception. However, in a second case of intussusception involving an adult there was no significant worm burden and the aetiology was obscure."

The squirrels also had viruses and bacteria, in case you want to have a squirrel week across all three "this week in" podcasts, end ectoparasites and fungus if you want to expand to five podcasts.

Suzanne writes: 

I couldn't remember being tested for Toxoplasmosis with any of my pregnancies while listening to your most recent podcast so I looked it up. According to most women aren't tested automatically these days. I didn't find any specific recommendations anywhere, though, so maybe it's something that depends on the doctor.
I do remember tests for AIDS and Hepatitis. Especially since with the most recent one the lab gave me someone else's positive Hepatitis result and missed my anemia :p
These days they just tell every pregnant woman to avoid under cooked meats and litter boxes.


PS It's cold down here in central Texas! I can translate easily from Fahrenheit to Celsius because it's been hovering just above 32F/0C for the last few days. We may even get what passes for snow around here... a few flakes mixed with the rain. I expect by next week it'll be shorts weather again, though.

Maybe that would make more sense as While listening to your most recent podcast, I couldn't remember being tested for Toxoplasmosis during any of my pregnancies...

Sam writes:

Hello TWIP! I write to you again from Tucson, where we are having quite a warm December. Today was a beautiful day, 75F, with sunshine and scattered clouds.

I was listening to Dickson explain the difference between Plasmodium vivax and P. falciparum on a historical TWIP whose number I don't recall, when later that day what should I read but the links below, reporting P. vivax infections in Duffy negative humans. The articles report that duplication of the Duffy binding genes seems to enable infection even without the Duffy receptor (per another report is expected 12/5, in just a few days).

It seems odd to me that duplicating this gene would have this effect - after all, wouldn't this be like having multiple keys to a door with no lock? It must be using a receptor of some kind, right? If it's not using Duffy, then it must be using another one - is Duffy part of a family of related receptors, or has the gene duplication produced a match for some other receptor altogether? I also wonder how this mutated parasite will fare in ordinary Duffy positive humans. I'd love it if you all could revisit this topic on the show.

On an unrelated note, I must say that the presentation of this open access paper (link below) is really great. No truncated article, clear navigation and organization, and it even includes a twitter interface. Three cheers for PLOS!

Thanks again, Victor and Dickson, for the podcast - Sam







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