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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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