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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 (http://www.jstor.org/stable/1375239)

[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 (http://www.jstor.org/stable/3222088)

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 experiment.com 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.


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