Anthony writes:

I’d not heard of knockout rats before the TWiP 139 paper discussion.  

As luck would have it, last Saturday I happened upon a December 2009 issue of Science.  On the back cover there’s an ad for knockout rats.  (Image attached.)


Case guesses:

Wink writes:

Dear TWIP Professors,

I read that onchocerciasis and loiasis can be found in Gabon and Cameroon. I would try to diagnose these in the Peace Corps veteran’s case. Onchocerca volvulus microfilariae can be found in skin snips from the lower body stained with Geimsa and/or by PCR. Loa loa microfilariae might be found in concentrated midday blood stained with Giemsa or Wright’s stains and by PCR, if available. I am thinking that other chronic metazoan infections, such as Bancroftian filariasis, are less common with her history. Thanks, as always for the challenging cases and insightful discussions.

Wink Weinberg


Iosif writes:

Dear Triple Twip,

For our patient with a travel history to Gabon and Cameroon and asymptomatic eosinophilia I would stay more on the conservative side of treatment depending on how severe the eosinophilia is.

The most important thing I could do is probably get a more thorough history and physical exam. Parasites aren’t the only things that cause eosinophilia; so I would ask if there were any new drugs that were started two years ago or a history of allergic symptoms or autoimmune conditions. Weight loss or systemic symptoms in these last two years could also rarely suggest a malignancy or an allergic eosinophilic syndrome.

I would also focus on any free river exposures or food exposures that could suggest a chronic strongyloides, schistosome, or another worm infection.

I would get a CBC and a CMP to monitor if there are any other organ involvement (such as iron deficiency anemia due to blood loss or liver enzyme release from schistosomes) and to monitor the eosinophilia. If there are no findings and no other positive lab results; I believe that I would monitor the patient for signs of organ involvement every 6 months to 1 year. I wouldn’t be in much of a rush to order more testing without more evidence to suggest a problem. Uptodate states that 50% of people with eosinophilia never have a definitive cause attributed and tend to do fine. I would reassure the patient then as much as I could


Iosif Davidov

Hofstra SoM

Class of 2018

Lachlan writes:

Dearest TWiP,

I am not sure if I am too late to write in for TWiP 139 – I have been on a “TWiP binge” these past few weeks and can’t help myself.

A quick note about the Peace Corps woman with eosinophilia. Thinking first about the pace of our evaluation, I did not pick up her absolute eosinophil count from the podcast. However, given that she is asymptomatic and has been in West Africa for 2 years doing good deeds unhindered by her blood count, the problem is probably not urgent. To develop symptoms, of course, there needs to be not only excess eosinophils in the blood but some pathological factor driving activation and tissue infiltration.

Not to call you predictable, I suspect infection in this case. In this area Dr Griffin has taught us well – my immediate thoughts are of invasive helminthiases such as strongyloidiasis, the “odd protozoa out” (Cystoisospora belli, Sarcocystis spp., and Dientamoeba fragilis), and even possibly intestinal Diphyllobothrium latum infection. Apparently even ectoparasite infestations like scabies can cause eosinophilia. Next they will be saying that Ekbom syndrome can too.

Common things are common – I suspect Strongyloides as it apparently can cause chronic infection lasting decades, helped by its ability to complete its life cycle in humans, an ability shared only with Capillaria philippinensis as far as I know. Chronic infection can be asymptomatic in over half of patients and causes intermittent eosinophilia in the majority.

Running with this hypothesis, I wonder from whence the worm came. Strongyloides is a geohelminth and I am eager to hear whether this woman has a penchant for barefoot activities at home or abroad. Perhaps she went on a shoeless peregrination on a previous trip to tropical parts of Asia or South America, or maybe in one of the endemic foci in the United States. Somewhere along the line she has encountered a third-stage filariform larva, which quickly made its way through the skin, venous system, lungs, and trachea to its new home in the small intestine. Apparently the parasitic females only live for a few months. Chronicity is explained by autoinfection whereby eggs hatch into first-stage rhabditiform larvae and are able to complete subsequent moults within the host, after which they penetrate the distal colon or perianal skin to complete their life cycle.

This woman has been asymptomatic for years. She probably has a light infection, with her immune system managing to keep the threadworm population at stable low levels over time. She also may have not taken note of the transient symptoms of larva currens and eosinophilic pneumonia as the worms happily go about their lives.

This might sound like a match made in heaven, hardly fitting the bill for “parasitism” – but diagnosis and treatment now will prevent her from developing hyperinfection in the future, as she ages and should she need to be immunosuppressed for some other medical condition.

Diagnosis rests on finding larvae in faeces, or antibodies in serum. Stool microscopy is insensitive because of intermittent and low-level shedding, requiring multiple specimens over a period of time. Concentrating the specimen or Harada-Mori culture might be helpful with this. As expected from how quickly the eggs hatch, the usual form in the stool is the first-stage rhabditiform larva rather than the egg or adult worm. A positive Strongyloides EIA would be good supportive evidence but the parasite still needs to be definitively identified, since antibodies to other nematodes can crossreact. Alas PCR is probably the way of the future.

The best treatment is ivermectin, which rose from an ignoble origin in a sample of soil from a Japanese golf course to become the treatment of choice for many helminth and arthropod infestations. By activating neuromuscular chloride channels, ivermectin hyperpolarises and paralyses the nematode’s pharyngeal musculature, presumably causing it to undergo a slightly inhumane death by starvation. Luckily these channels are sufficiently different from human ones that we, too, are not paralysed at the usual doses. 200 micrograms/kilogram once daily for two days should be enough, with followup stool and serological evaluations for at least a year to ensure eradication. In her case, we would also hope that the eosinophilia resolves.

Prevention of future infection is with … shoes.

Hope this is not way off the mark for my first try. I’m a regular listener but have never before ventured out into the open. You guys have kindled in me a new interest in parasites and tropical medicine. Eternally grateful.


Medical student

Brisbane, Australia


Steve writes:

I expect that the TWiP team are already aware of this sad report on the return of once eradicated parasitic diseases with increasing inequality and poverty. But I thought I should pass it on, just in case.

All the best,




Peter writes:

Dear TWiP team,

Having looked at possible causes of ocular parasitosis in a teenage girl from New York I feel that the parasite that fits this case is nematode  Baylisascaris procyonis.

Baylisascaris infection is caused by a roundworm found in raccoons, larval migrans results from accidental consumption of Embryonated B. Procyonis eggs. After an animal or person swallows Baylisascaris eggs, microscopic larvae hatch in the intestines and then move into the bloodstream and tissues causing damage as they grow. There is a significant risk that the worm seen in her eye is not the only one in her body.

I found this recent article on Baylisascaris infection

John writes:

Hi TWiP casters,

I very much doubt this is the answer to the case study, but given the timing of the TWiP episode and the BBC news article, I thought you would find it interesting.

Thelazia callipaeda



Dave writes:

Good Doctors. I was listening to our Quirks and Quarks, our Canadian science show. Bob Macdonald was interviewing a journalist who was with an expedition to eastern Honduras( the show aired Aug 26 2017). Douglas Preston( the journalist) described going to Honduras to check out a lost city with a curse on it. It’s a great story but what interested me was the curse. It turned out to be Mucocutaneous Leishmaniasis( hope I got the spelling close). He(the journalist) went on to tell how most of the people on the expedition caught the disease and that the treatment was almost as bad as the disease.

Douglas Preston wrote a book about the adventure “Lost City of The Monkey God”. Would be interesting to hear your take on the story and the accuracy of the effects of the disease.

Thank you for the great podcast and all your efforts to educate the world

Shearer Dave From Southern Alberta where it’s finally raining. Woke up this morning to 1c. The high for today 8c

Anthony writes:

“As first alluded to by Tiner (1952a), there is good evidence that paratenic hosts, particularly grain-eating rodents, become infected with procyonis by foraging for undigested seeds and other materials present in raccoon feces at latrines (Wirtz, 1982; Kazacos and Boyce, 1989; Sheppard and Kazacos, 1997; “

Baylisascaris Larva Migrans

By Kevin R. Kazacos

# # #

Yes, raccoons can be infected with Baylisascaris from each other, but that’s not the most interesting form of transmission.  Rodents are attracted to raccoon latrines as a food source.  The larva migrans disable or kill the small animals — enabling raccoons to catch and eat them and so become infected.

Here the parasite is not trying to kill its host; it’s trying to kill its host’s dinner.  Might the arms race paradigm be misguided?

I’d think it curious — if not comical — if someone tried to explain evolution by looking at a black and white photo of coral reef fish and then using peppered moths as a model.  Why is virulence similarly seen as operating along a single axis?


Anthony writes:

McLuhan in New York – at Fordham University, Friday, October 13, 2017

If I remember correctly, you’re teaching a photography course at Fordham.  This event is in Manhattan at the Lincoln Center campus.

McLuhan’s son Michael is a photographer.

I don’t know if he will be there.

In one of the early episodes of your This Week in Parasitology Podcast, you mentioned Ulysses by Joyce.  I found this audio of a dramatic reading very good:

Joyce’s works mentions a virus (the letter to the editor) and parasites (the fingers blood-stained from picking lice).  Joyce was a aware of  disease — something that McLuhan and Chardin it seems overlooked.  Burroughs focused on this aspect of modern times / the global village:

According to my understanding of Marshall McLuhan, it’s not that artists predict the future, but that they see the present. The illusion of prophecy results when everyone else is looking backwards instead of ahead.


Veronica writes:

thank you my friends, for still cranking out your podcast! I haven’t listened for awhile and I’m happy to hear the familiar sounds of your voices, and the intro-outro music. I was soothed! How we relax best with our own most familiar cultural constructions. Last night I came home from Thanksgiving dinner full of  wine, whiskey, turkey, 7 different vegetables, AND a piece of cannabis brownie. The conversation at the table was very stimulating (thanks to the rather existential state of the world) and my host suggested a little brownie might help me settle down when I went to bed. No, it did not! My mind was racing! I searched my fave podcasts and realized I hadn’t tuned in to TWIP for a year. So there was I, high, and analyzing your every word, and segment change, fluctuation in tone and intake of breath. You guys totally passed the test of close scrutiny! As before, you shifted from the language of biology to humour,  to empathy and kindness and back to biology. I wrote you before once, and I had to write to you a second time to say hello and bravo.

I am not a biologist, I got my degree in Art and History. I can barely follow your ideas sometimes, but am fascinated by the fact that you all seem to know exactly what you are talking about. Somehow I learn something. I didn’t have to listen twice to understand that a young New York female contracted a parasite that uses raccoons as its host, and burrowed, over perhaps 10 years, from her gut to her eye, and that because it moved, wiggled in her eye the ophthalmologist and his team were able to figure it out what it was and how it got there. That is amazing! A worm can travel through the human body, transfer through the different membranes and organs without detection and finally emerge to disturb the eyesight of a teenager. I know Schistomiosis (i know i spell it wrong!) is like that, can penetrate the feet i think?

if i remember from Dixon’s lectures?

I would love to hear a podcast that explains that body thing, how parasites move within their hosts.

love you, and thanks, Veronica