Case guesses:

Peter writes:

Balantidium coli infection

Robin writes:

Would be some organism that does not provoke the appropriate immune reaction to produce excess eosinophils and Charcot-Leyden crystals.

Isospora produces both. Cryptosporidiosis produces neither. Microsporidiosis is a veritable bag of worms; Cyclospora is acid-fast and fluoresces in fluorescent microscopy, and would seem to be the best guess.

Wink writes:

We need some new wound-healing magic. I hope it comes from Opisthorcis.

My wild guess for the most recent case is Balantidium coli. This is because, as a protozoan, it doesn’t cause eosinophilia, and because pigs may be carriers. In the case of the 10 year old helping to prepare and cook pigs, her drinking water may have become contaminated.

Wink (Atlanta)

Allan writes:
Aloha Doctors TWIP,

Its 27ºC, partly cloudy, with moderate VOG (volcanic fog which makes the horizon blurry), and high surf warnings (25-35 ft waves).

Pig hunting is very common here as well. Of the parasites I can think of that can be caught from pigs… here’s my thumbnail differential:


If they were not positive they had only eaten well cooked pork, I might suspect the diarrhea and fever were from the enteral phase of a trichinosis infection, but that seems unlikely, as the food preparation seems the suspected exposure.

Balantidiasis can certainly causes diarrhea but rarely fever.

Cryptosporidiosis could cause diarrhea, possible weight loss and diffuse abdominal pain and fever…. and the incubation period is about right ( 1 to 12 days; 7 days is typical).

I have also seen patients with diarrhea and fever who are avid pig hunters who were suffering with concurrent infections of Dientamoeba fragilis and Blastocystis hominus

Blastocystis hominus seems to cause diarrhea more often than we once thought, but rarely fever.

Dientamoeba fragilis can cause both diarrhea and fever by itself (and they’ve recently identified a cyst stage in its lifecycle, although transmission still seems associated with Ascaris or Enterobius eggs.)   Still, these last two are rare.

So I will go with a guess of Cryptosporidiosis.

To nail it down, one could try to find C. parvum after floating the feces in a sucrose or zinc sulfate solution. Mature oocysts are 4–5μm in diameter and appear red after acid–fast staining.

Of course if you’re at the CDC, you can use Immunofluorescence as well.

If your patient is immunocompetent, then it may well be self-limiting, but I look forward to your discussion on treatment. I think nitazoxanide is approved and in the past paromomycin and azithromycin have also been used with some success.

And of course I may have totally missed something.

As always your approachable way of teaching and making us think is appreciated.

Best regards,


Kona, Hawaii

Iosif writes:

Dear Twipyzoites,

Hello! I am a second year medical student, and I’ve been listening to your podcasts since we had our microbiology course. I found listening to Twip, Twiv, and Twim were great ways for me to continue to pique my interest in the subject and keep me sharp for my exams. This is the first time I’m responding so I hope it goes well. The weather this past week has been truly on a roller coaster ride. With the blizzard over the weekend and the near 50 degree (Fahrenheit) heat wave these past two days, I no longer know what to expect. Right now it is cloudy and 39 degrees with 50% humidity.

For the differential this is what I am thinking:

Primary Diagnosis: Balantidium Coli. It is rare for this parasite to infect people in developed countries, but is somewhat common in tropical areas. It is usually obtained from pig feces in unclean food or water (or hopefully in this case from an unclean pig directly). After the cysts are ingested, the cyst walls degenerates and the trophozoite invades the intestinal wall. If the infection is serious enough, then there could be ulcer formation and bleeding which could lead to the microcytic anemia that the patient has. Diagnoses is by finding cysts or trophozoites in the stool.

Other parasites:

Ascaris: Could cause the symptoms, but it is not that rare and should have been eliminated with proper cooking of the pig.

Sarcocystis/Taenia/Trichinella: All should have been eliminated so long as the meat was well cooked.

Cryptosporidium: Usually obtained from unclean water and not directly from pigs (except maybe their feces). It is also somewhat common.

Non-parasitic causes that should be kept in mind:

Campylobacter, Yersinia enterocolitica, Salmonella, Tropical Sprue.


Celiac Disease, Ulcerative Colitis, Crohn’s disease.



Elise writes:

Dear TWIP Trifecta,

How are you all? I hope this finds you well. Many apologies for missing a TWIP 100 (!) diagnosis attempt. I was working on an educated guess and got derailed by the debris of life. Having said that, I am pretty sure I would not have gotten the correct diagnosis. The weather here in lower Manhattan is cold and bright (39 degrees F/-13C), but I would say appropriate for the season.

This week, I am going to hazard a guess, but I am also sure that I won’t get the answer right.

The little girl in a country that is not the United States has had diarrhea and a low fever for several weeks and all of the clues indicate that she contracted a parasite after helping butcher and prepare a wild pig, which she ate with her family.

I understand that this is going to be a tricky diagnosis, in part because this case was rather unusual in that wild pigs don’t generally transmit the parasite to humans and because this is an unusual parasite. I actually went back through all of the early episodes of TWIP in hopes of being able use process of elimination to help with my diagnosis, but I realize that is a lazy approach and this time it was surely unsuccessful.

The little girl’s symptoms are consistent with a couple of parasitic infections. First, it resembles cryptosporidium. Wild pigs to tend to carry it and while humans can’t contract a crypto infection through blood, it is very possible that the little girl came into contact with the wild pig’s fecal matter during the butchering process. This doesn’t seem to be an unusual enough parasite, but I would put it in the category of Likely Suspect.

The only other parasite I found that seemed like a good bet is Balantidium coli. This is another not-perfect fit for a diagnosis. The symptoms match, but again, blood contact is not necessary and it doesn’t seem to be quite unusual enough.

I appreciate that these diagnoses are getting harder and I do welcome the challenge but I do realize it is testing my resources. Is there some way to acquire a more recent edition of Parasitic Diseases? I have seen the third edition available online but I know that there are more updated ones.

I promise to do better in the future and many many thanks for your excellent podcasts.

Best wishes

Anne writes:

Dear TWIP team

My thoughts for the diagnosis of the young girl in Week 101: I am stumped.

The microcytic anemia suggests iron deficiency due to blood loss, the case presentation and Daniel’s hints that stool examination is diagnostic suggest that this is a primary enteric infection and none of my differentials seemed like perfect fits.

I am going with Balantidium coli, a ciliate protozoan parasite. It is associated with pigs, is an uncommon parasite, does not cause eosinophilia, and can cause diarrhea, dysentery, abdominal pain and weight loss. Clinical signs are most common in the immune-suppressed according to the CDC. However, I have found no discussion of fever or microcytic anemia. And though young age (10 years) could represent immune naiveté it isn’t immune suppression.

My other considerations were:

Ternidens deminitus- rare African and Asian helminth of nonhuman primates– can cause iron deficiency anemia per one reference, not supported in another reference; minimal clinical signs in humans and no association with pigs.  

Trichuris trichiura- whipworm- possible association with pigs, with high worm loads may see loose frequent stools, frank blood, straining and rectal prolapse; is associated with blood loss and anemia. Variable eosinophilia.

Hookworms (Ancylostoma and Necator) can certainly cause blood loss and variable eosinophilia, but patency period is usually 1.5 to 3 months. Of course the pig hunting trip could be a red herring.

Looking forward to the answer rather than list every other enteric parasite I examined and dismissed.

Anne Lewis, DVM, PhD

Beaverton, OR

Wytamma writes:

Dear TWIP Hosts,

In TWIP 100 (Driving past a milestone) you spoke about the loss of transgenes from mosquitos due to natural mutation. Would this Idea work to keep the Cas9 gene from mutating? incorporate a selective pressure/lethal gene/s that the CRISPR system disrupts. This way the mozzies have to keep the Cas gene or the selective pressure gene will reduce their fitness?

Great to see you reach the 100 mark! hopefully many more to come.

All the best,


Chandran writes:

Greetings TWiP fellows!

I’ve been listening to all of Vincent’s podcasts on the weather network for a few years now and find them all exceptionally entertaining, interesting, and educational. Today I write in for the first time from down in Australia.

I’ve been very much interested in the CRISPR system and all of its applications in molecular biology since I first heard about it on TWiV or TWiM (I forget which) a couple of years ago while I was doing my undergraduate degree. Back in the present, I have literally just started my PhD last week and the major focus happens to be on the gene drive system!

I wanted to provide a comment and a question in response to TWiP #100’s discussion of the gene drive paper by Gantz et al:

One thing Vincent mentioned was that a flaw with the gene drive is that if the cas gene ever gets mutated then it disrupts the whole system as it can no longer spread. This isn’t really much of an issue however as the allele with the mutated cas will still only spread throughout the population in a Mendelian fashion, whereas every other copy of the gene drive in the population with a fully functional cas gene will continue to spread in a super-Mendelian fashion with those incredibly high inheritance rates of >90%. In addition to this, that allele with the mutated cas will still be carrying a functional copy of whatever kind of cargo genes you’re trying to spread through the population so will not hinder the other copies of the gene drive with still-functional cas.

I was also intrigued and a bit mystified by Daniel’s comments in regards to not wanting to wipe out a single species of mosquito. Earlier in the podcast he seemed to be making the opposite case as he pointed out how many people died per year from malaria and that should be the priority in these kinds of decisions?

Keep up the great podcasting!



Carie writes:


I very much enjoyed listening to your podcast for the first time today! I’m a veterinarian studying for a board exam (American College of Veterinary Preventive Medicine), which encompasses public health as well as veterinary medicine, and your podcast was recommended by a fellow candidate.

I wanted to say that, not only should your textbook get in the hands of all medical students, but also of all veterinary medical students! 🙂

I look forward to hearing more of your podcasts.

Thank you, and best regards!


Anne writes:

Dear TWIP team

During the discussion of potential mechanisms for the publication of the sorely needed updated parasitology text, it occurred to me that one of the potential resources not mentioned was the Gate Foundation. So much of the Gates Foundation focus is on global health initiatives with an emphasis on the diseases of the developing world, I would think this project fits well into their overall goals, even if it it is not something that fits the typical research project paradigm.


Beaverton, OR

Anthony writes:

Pinworm in 7000 year old Iranian

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