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TWiP 20 Letters

Jim writes:

For TWIP file (link).

Smithfield, VA

Marc writes:

Dear Vince and Dickson

Wonderful job on both podcasts. I just finished listening to the Cryptosporidium episode. I love all topics regarding the apicomplexa, and unless I am mistaken there is a fascinating aspect of this phylum which I have not heard discussed on your show. This is the apicoplast. As I am sure Dickson is aware some time in the early 1990s a degenerate plastid was discovered in Plasmodium and later discovered in most apicomplexans. Interestingly it was also noted that Cryptosporidium lacked this organelle and present evidence indicates that gregarines (another type of apicomplexan) also lack a plastid. The presence of this plastid is interesting for many reasons. Primarily this organelle may provide drug targets that would not interfere with host biology (due to the cyanobacterial origin of plastid). However what I find most fascinating is what this implies from an evolutionary perspective, that modern day bloody parasites like Plasmodium have an algal/photosynthetic ancestry. Talk about wild evolution! This has been exemplified by a discovery in 2008 of Chromera velia, a photosynthetic alga that is close phylogenetically to the apicomplexa. Evolutionary implications of this plastid are indeed fascinating from both the perspective of horizontal gene transfer as well as the evolution of the relationship between these parasites and their hosts. These relationship are ancient, indeed! These discusisons tend to stray from topics regarding virulence however I feel your listeners would enjoy hearing something about the evolutionary history which developed these truly chimeric yet single-celled critters!
Keep up the good work


Carolyn writes:

Dear Vincent and Dick,
I am really enjoying your podcasts on parasites. I took special note of the one you did on cryptosporidium.

I am a 52 year old beginning backpacker. In doing the research on water purification, I found that giardia and crypto were the two that came up the most. Since I would prefer not to use a mechanical filter and don't mind the taste of chlorine, I want to use a Miox system. (a super-chlorination system using table salt and a battery) The instructions say that it kills giardia within 30 minutes, but it takes 4 hours to kill crypto.

In listening to the podcast, I found that every time it looked like some questions might get answered, the point of the topic shifted to something else.

Here are the conflicts I have:
When I hiked Pikes Peak, the Barr Camp personnel said they only knew about protecting against giardia. Is crypto not something to really worry about? Or is it really everywhere?

You mentioned immunity. If a person is immune, does that mean they won't have symptom? Symptoms are less? I drank out of a lot of creeks and even ditches when I was a kid. Am I immune?

You said that chlorine won't kill it. Will Miox solution kill it in 4 hours, or are the instructions wrong? (The army uses miox)

I REALLY don't want to get sick, but I can't lug around gallons of water everytime.


Sam writes:

What about this for a catch line:

Another twip is hosted.

Another twip is vectored.

Another twip is spiral.

Jesper writes:

All in the Mind, a great radio show from Radio National Australia mainly about things pertaining to the brain, did a show about
parasites and their effect on populations. You'll find it on
including a transcipt.

One comment references RadioLab, which I must assume is the one where Prof Despommier was featured.

All the best,


Felix writes:

Hi Prof,

I don't think in your program on Crypto that you actually said by what mechanism it causes diarrhoea.
Whereas you have given similar explanations for other organisms.


Atila writes:

Dear Twipers and Twivers,

After listening to all TWiPs (although I will listen twip 19 in some minutes) I have noticed many readers send suggestions of parasites that manipulate hosts behavior, such as Cordyceps fungus. So, I wanted to make my contribution too, and add to the discussion of modifying mosquitoes to bite less and decrease malaria transmission.

The problem I see in this approach is that the plasmodium already does it! Plasmodium is able to make the infected mosquito bite more frequently, thus increasing its transmission:

Koella, J. C. (2005). Malaria as a manipulator. Behavioural Processes, 68, 271-273. doi: 10.1016/j.beproc.2004.10.004.

Also, it is not only the mosquito that plasmodium can modify. It makes infected people more attractive to mosquitoes:

Lacroix, R., Mukabana, W. R., Gouagna, L. C., & Koella, J. C. (2005). Malaria infection increases attractiveness of humans to mosquitoes.PLoS biology, 3(9), e298. Public Library of Science. doi: 10.1371/journal.pbio.0030298.

As a regular TWiV listener (and a big fan) I like the differences between the two podcasts. Professor Despommier's impeccable narration (I liked this letter) makes parastism really interesting. I had a terrible impression of parasitism in college, it is a big topic of biology in Brazil, since there where many parasitic diseases here not so long ago, and some parts of the country still have it, and the lectures were all focused on long life cycles a lots of different names.
Only after reading the histories behind the diseases, the patients and the discoveries, as well as learning the host-parasite interactions I started to like this topic. Carl Zimmer's texts had a big role in this change and I am very fortunate to hear someone with so much experience and personal history as Dick Despommier in TWiP. Specially now that he is a busy popstar and bestseller writer.

Long and prosper success to TWiP,


p.s. I have great expectations for the guests you may invite, given the quality of TWiP and the guests of TWiV.


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