Mark writes:

Temperature in Oklahoma is 12 degrees C today and rainy.

My guess is Tunga penetrans which is native to South America. The black point at center of itchy toe lesion is the flea which are legs, spiracles and egg laying aparatus. Female flea burrows into skin and resides in sand or dirt which is where professor came in contact with flea. Treatment is surgical incision. If the burrowed female flea dies, the lesion can become infected.


Peter writes:

Greetings TWiP team.

This week’s case study seems to be a good match for Tungiasis, caused by the chigoe or sand flea, Tunga penetrans.

Gravid female Tunga penetrans burrow into exposed skin on the feet of mammals and remain there for two weeks while feeding on host blood. The flea will swell dramatically as it feeds and its eggs develop, sometimes causing intense irritation.

Infection is characterized by a swollen red lesion with a black dot at the centre, this black dot is the flea’s exposed hind legs and respiratory spiracles

Treatment is surgical extraction of the flea, followed by thorough cleaning of the wound and application of topical antibiotic to prevent secondary infection.

This case is fortunately just one flea, however people in the developing world can have seriously debilitating infestations of many fleas.



Carol writes:

Greetings Doctors.

In keeping with the Hallowe’en episode theme, I would like to believe that the unfortunate professor in this week’s case study contracted a new parasite that results in complete zombification of the host, but alas (or fortunately) that would not be the correct answer. I think I would have heard about a zombie rampaging in New York. A more realistic guess would be that he is host to a sand flea, specifically a gravid Tunga penetrans. Much like Dickson, I recommend removal; but not of the whole toe, just the flea and/or the nodule she is living in.

Carol in Victoria, where it is sunny and 10C; winter has truly begun.

Venkat writes:

Dear Twip team,

I was way off in guesswork last time but hopefully I redeem myself in Twip 98. I think the professor could have acquired ‘Tungiasis’ caused by the parasite Tunga penetrans. It is quite common in south America; and his visits to the beaches and the characteristic black dot, gives away the diagnosis. It was awful to read about this disease, and hopefully he can get rid of it, which as of today typically requires surgical removal. Several topical drugs are available but none seems to work best. I also read that the disease has become a major burden in Africa where it is believed to have been imported from outside. I remember writing that I am fascinated by parasites, but I will reconsider my position after this case. I think they are disgusting 🙂

Vincent, I like your approach to eradicating diseases by culling the mosquitoes but not sure if it is entirely beneficial. For all we know about molecular biology and epigenetics, the mosquito may contain a protein yet to be discovered, which could become a life-saver. There are plenty of examples in the microbe world where they contributed a wonderful drug to the humans to heal themselves. Yes, we cannot simply stand back and let them threaten us. At the same time, we have to be sensitive to the fact that what we are disturbing is the formidable Nature itself, and its grand design. It will stage a bigger comeback!

Venkat B

Alan writes:

Good morning professors,

Dx Tungiasis, Caused by the female Tunga Penetrans flea.

Tx surgically removing the flea.

Thanks for your fascinating and informative podcasts, especially This Week in Parasitism.


Alan L. Sampson, M.D.


Currently living in the South Loop of Chicago

Zachary writes:

Dear TWiP Docs,

It appears as though this 50-something professor has been jiggered! Tunga penetrans, otherwise known as the chigoe flea, is the culprit here. This flea is native to Central and South America. The female of the species burrows into the skin to lay her eggs causing a condition known as tungiasis. Treatment is surgical removal of the flea followed by a topical antibiotic ointment to prevent secondary infection.

This flea is not to be confused with the North American “chigger” that we have here in the states.

The ground is frosted and hard here in eastern Washington as it is currently 0 degrees C. At least the sun is out. No snow yet but I am hopeful for a plentiful snow pack to accumulate in the Cascades this year.

Keep churning out the great episodes!


Elise writes:

Dear TWIP Trifecta,

As always, many thanks for your podcast. I missed the previous case study due to an onslaught of life minutiae, but am back and will hazard a diagnosis for the Professor freshly returned from Brazil who discovered an itchy, growing lesion on his toe.

I suspect that the Professor has Tungiasis, which is also called bicho do pe in Portuguese (the translation of this is “foot bug” — though this moniker is not the only reason I make this diagnosis). Tungiasis is caused by female sand fleas, which burrow into skin, usually in their host’s foot. Once inside the host, the flea drinks blood, lays her eggs and dies, after which the eggs fall out of the host. Even though the professor wore flip flops on the beach, it is still possible for him to have contracted the flea because his toes were still exposed to the sand.

To double check my thinking, I did a Google image search and Dr. Griffin’s description of the patient’s toe nodule was so detailed that it was very easy to feel a little more secure in my diagnosis.

If the lesion was growing, (and if I’m correct) does this mean that the parasitic flea was about to release her eggs? I read that there is the opportunity for secondary infections in the spot where the flea once resided. What is the appropriate treatment?

Does this mean that one really needs always to wear full shoes on the beach? If so, that’s a bit of a disappointment.

Thank you so much again for your work, and I look forward to hearing TWIP 99.


Jon writes:

After a night of debauchery, a single female flea of the species Tunga penetrans, lost and alone in the world searches for a warm safe place to raise a family. Having neglected protection during her last sexual encounter, she is now pregnant and alone in the world. All seems lost, lacking the body warmth to and resources to grow her offspring, she searches for a new hope. On the horizon, a figure looms, meandering towards her, rushing and hoping to secure a safe she leaps at the figure. Finding herself on the toe of a professor, she relishes in her new found home and burrows into the skin. Little did she know that this was the calm before the storm, as her new host was going to discover her and she would be in for the fight of her life.

My guess is a Tunga penetrans infection. Grab a kitchen Lydocaine, knife, Windex (disinfectant) and chop it off.

I may have anthropomorphized the flea slightly, in that she is a flea and not a human.

This would be my first email into TWI podcasts, I have listened to all of the podcasts, and am a huge fan.

Jesse writes:

Dear Twipsters,

Here’s what Dr. Google, and Mssrs Wiki and Pedia, instruct.

The erudite and sandal shod traveler of Brazilian beaches has likely acquired a case of tungiasis, wherein a burrowing female sand flea, Tunga penetrans, has established her nursery in the sub-dermal skin layers of his big toe. T. penetras is thought to be originally native to the West Indies and was described by the Spanish in 1526. European traders and their unshod crews quickly spread this nasty creature throughout Latin America and West Africa.

The dark center spot in the lesion are the female flea’s lady bits, anus, and rear air holes sticking above the skin to attract gentleman passers by. The females belly swells with the growth of several hundred eggs which she excretes over the course of several days. Eventually the mother dies but her expelled eggs develop in the soil to start anew.

While not an avid jumper they do have a 20 cm vertical leap so flip flops don’t provide complete protection. A successful repellant is said to be Zanzarin: made from coconut oil, johoba oil, and aloe vera. Shoes and frequently swept concrete flooring are the most effective preventative measures.

YouTube contains many graphic images of rough field surgeries set up to remove dozens of gravid female “jiggers” from the sore and battered feet of people suffering from an infestation.

Thanks for the all wonderful podcasts, they really are a lot of fun.

Eric writes:

Dear TWiP triumvirate,

I am writing with a guess for the case of the week for TWiP 98. I will guess that that gentleman has returned from Brazil with an unintended souvenir in his big toe consisting of a single chigoe flea, or Tunga penetrans, a delightfully descriptive name. The locals might have called it bicho de pé. That central black dot is likely the tail of the flea itself, busily enjoying the nutrients in his toe.

Thank you for another great case of the week, definitely apropos of Halloween.

It is currently 55 degrees, raining, with 25 mph winds in Seattle, at the height of a typical November storm.

Hunter writes:

Greetings good sirs!

I’m a longtime fan of TWiP, though I’m just now finally caught up to the most recent episode. Ever since seeing Monsters Inside Me several years ago on NetFlix, I’ve been super interested in parasites, a fact that my friends clearly know well as several of them forwarded me the following article: (Man Dies After Tapeworm Inside Him Gets Cancer)

The thought that it’s possible to get tumors from non-human cancer cells is pretty trippy!

Anyway, thank you all so much for doing this podcast. I plan to start TWiV and TWiM soon, I just need to get all the old episodes that don’t appear to be on iTunes. I really enjoy the banter you guys have. The format of a conversation between a few people makes the information much easier to retain when compared to just having it lectured at you. Even without you being able to hear us, this format makes it easy to talk along with the show, as well as to tell other people about what you learned, all of which makes it stick.

I did have one final question though, what ever happened to Dickson’s parasite ebook? I’ve been hearing about it for years now (it took me a long time to catch up) and can’t afford any of the physical copies I find online. Plus, I like to be able to easily copy/paste information to people.

Thanks again for all that you guys do!

QA Analyst 3 : Hearthstone
Blizzard Entertainment

Theodore writes:

Dear Dr. Racaniello,

Just in case you have not been made aware of this just published article, thought it would be interesting for TWIP.
Thanks for your continuing work on all your wonderful podcasts.

Peter writes:

Greetings TWiP team, I saw this report in Nature and thought it would be of interest.

An HIV positive man infected with the tapeworm Hymenolepis nana developed a cancer like disease caused by invasive cells of the tapeworm.

The invasive cells were discovered in biopsy samples from the patient testing found them to be non human and genetic sequencing showed them to be tapeworm cells. Researchers think that the the cancer like cells resulted from the interaction of stem cell rich larval tapeworms with the faulty immune system of the patient.


Robin writes:

Dr. Wink writes:

Amazing report!

As you are probably aware, there was an amazing report in the New England Journal of Medicine yesterday that is worthy of mention on TWIP.

Malignant Transformation of H. nana in a Human Host
November 5, 2015 | A. Muehlenbachs and Others
In this case report, malignant transformation and metastatic spread of Hymenolepis nana, the dwarf tapeworm, was identified in a patient with advanced HIV infection.”

Malignant Transformation of Hymenolepis nana in a Human Host


Maria writes:

Hello, i am maria from mahidol university thailand.
I am interested in knowing the types of virus that infect plasmodium parasites. Where can i get that information?
Thank you
Mark writes:


It is cool in Muskogee Oklahoma today. High was around 65 degree Fahrenheit and low around 41 degrees. It is nice fall weather.

I am a little late in determining a possible guess on case number 97.

My guess is balamuthia mandrillaris, a pathogenic soil ameoba found in soil. The description of the painless brown skin lesion on the knee in 12 year old girl and the face lesion in 5 year old boy coupled with cognitive disorders and encephalopathy from lesions in the brain is why I suspect this possible disease. This is considered an emerging disease and it is known to occur in South America. A Thai review article case report I found indicates it is pretty rare disease.

I don’t know how rare it actually is if Daniel encountered two similar cases in Peru?

As the above case and review article indicates this pathogenic amoeba gains entrance into body through skin abrasion or through inhalation or oral ingestion.

It is lethal if left untreated. The Thai case report/review lists a 2010 case where patient from Peru was treated with itraconozole plus albendazole for 14 months. Other cases described in review article indicate that this is a really nasty disease that requires surgical excision of lesions plus anti parasitic medication. Korean case report and review conclude their case report with suggestion of macrolides, such as clarithromycin plus azoles. Their patient, a previously healthy 4 year old child had a terrible outcome.

Disease may not be easily diagnosed because it had an indolent course.

Hope this terrible guess is not what these patients have, and I am entirely wrong.

I kind of ruled out visceral leishmaniasis because from what I understand, it would be kind of rare for encephalopathy to develop.


PS It is difficult to distinguish acanthamoeba from balamuthia. The two species are morphologically indistinguishable. Diagnosis is more easily confirmed by PCR, although immunohistochemistry or immunoflurescence are available at very specialized centers such as the CDC. Encephalitis caused by both is similar.

Nicholas writes:

Twip or treat my fellow ghouls and goblins,

As cerebral involvement was preceded in both cases by cutaneous lesions in association with a clinical history of epidermal compromise (scratches/scrapes), I believe the most likely etiologic agent for these cases is Balamuthia mandrillaris, which is one of many free living ameba readily identified in soil. In rare instances this organism causes multi-systemic disease, originating in either the skin or lower respiratory tract with subsequent hematogenous dissemination to the central nervous system. This condition has been documented in both immunocompetent and immunocompromised humans and multiple animal species. In fact this condition was first documented in a mandrill housed by the San Diego Zoo in 1986.

This is one of several ameba species that have been indicated as an etiologic agent of amebic encephalitis, with additional agents including Acanthamoeba spp., Naegleria fowleriParavahlkampfia francinae and Sappinia diploidea; although the cutaneous involvement preceding neurologic manifestation is unique to B. mandrillaris.

Although ameba look similar histologically, a few salient features utilized by pathologist include lack of tissue cysts with Naegleria fowleri and rare bi-nucleation for B. mandrillaris. A definitive diagnosis can be made through multiple ancillary tests including multiplex qPCR targeting the 18S rRNA gene, immunohistochemistry, and immunofluorescent antibody test. Because these cases are so rare, these ancillary tests are not routinely offered through most diagnostic laboratories, but are offered through the CDC’s free living ameba laboratory.

I had the fortunate opportunity of diagnosing the first case of B. mandrillaris in an Indian flying fox this past year (soon to be published in the Journal of Veterinary Diagnostic Investigation), which has further expanded host susceptibility to the order chiroptera for B. mandrillaris.

I’ve attached a gross image from the aforementioned flying fox case, which is characterized by malacia and hemorrhage emanating from the mesencephalic aqueduct in the midbrain. Additionally I’ve attached an image of the fluorescence assay performed in this case utilizing antibodies specific for B. mandrillaris, displaying strong apple green positive labeling of ameba trophozoites.

I would like to make a point that when a pathologist utilizes the term “gross” they are communicating what they were able to discern with the naked eye and not referring to an unattractive state of the lesions, which are in fact always beautiful through the eyes of a pathologist!

Happy Halloween and thanks again for the always entertaining and informative pod cast!
Pictures Nicholas sent:

Joshua writes:

Hello Doctors,

I want to let you know that I love the show. I’ve been listening since I started Pharmacy School in 2012 and I’ll be listening after I graduate this spring. I also wanted to let you know that I’m married to a very intelligent woman with a masters in fine arts. She teaches dance, both modern and ballet, and she is extremely knowledgable in her field. I, however, am just a lowly pharmacist in training. Typically we have a pretty efficient division of labor at our house where I answer the medicine questions, and she answers everything else.

Here’s where it has gotten tense. For some reason, I seem to remember an episode of TWIP where a parasite was mentioned that ONLY infects humans. My wife believes very strongly that there is no such thing, and after failing to impress her with my knowledge of dracunculiasis (apparently it infects dogs too) I’ve lost all credibility.

Help me doctors you are my only hope! Is there such a beast that only preys upon humans? Or for every boy with a worm, is there a dog on the worm’s menu as well?
My marriage hangs in the balance!

Joshua PharmD. Candidate
University of Charleston

Evie writes:

Dear Dr. Dr. and Dr.,

Firstly, I want to thank you for your work here on the show and in life. You three are amazing <3

About the show, you don’t know how many hours I’ve spent with you guys crammed into my ears, often times on long tourbus rides.

Which leads me into this Scabies Story…

A few years back, I was in a touring cabaret. We were performing in Italy at a gorgeous venue in a lovely town for a prestigious event. About three days into our stay, red dots started to appear between the fingers and up the hands of four of our troupe members. One kept saying “the mosquitos here are terrible” and scratching and scratching. I didn’t pay much attention as I was unaffected and this was a group prone to complaining. BUT, every night at the end of our show we would clasp hands and take the final bows. I begrudgingly participated, even during the “outbreak”. (In the end, I was not infected.)

The affected folks were convinced that the spread was due to unwashed bedclothes or towels in our hotel. However, I was not. Scabies have an incubation time right? The immediate reactions the others had would mean that they had contracted the parasite elsewhere, right?

Later, when we were all back at home, one of the members admitted that they had been exposed weeks before in New York. This explained why those of us who didn’t make the NY stop were free of the scabies.

As a person with a biology/clinical laboratory background, traveling was always scary. Eating food that had been sitting out and having no control over how it was prepared, loading all of your belongings on top of other people’s belongings and then the close proximity we all had with one another for hours and hours daily. Icky! I basically lived off of bread and wine, you know, for safety’s sake 😉

After this scare, I started leaving my bags in the car and parking atop a parking structure, letting the bugs bake to death in the California sunshine, just incase there were any stowaways.

I have a bedbugs story and an e.coli story too! Hooray for showbiz!!!

Much love to you three. Thank you again for all that you do.

Erwan writes:

Dear Dickson, Vincent and Daniel,

It’s great to finally be writing to my favourite podcasters. I really enjoyed your discussion on Twip 97 about natural antibodies against alpha-Gal mediating protection against malaria. But I have to correct you on one point. In that episode Dickson and Daniel both insist that mosquitoes inject sporozoites directly into the capillaries of their victims. Meanwhile Vincent, in vain, tries to argue that the sporozoites are injected intradermally. Well, Vincent is right. It’s been known for a long time that when mosquitoes take a blood meal they begin by probing the skin, and inject sporozoites from their salivary glands into the dermis. The sporozoites then migrate through the dermis to capillaries where the circulation of the blood takes them to the liver.

Here is a wonderful paper where you can see videos of the mosquito probing and releasing sporozoites. It is a sight to behold!

I’m working on a vivax malaria vaccine at the Jenner Institute in Oxford and listen to your podcast while checking blood smears of malaria-infected mice. Sean Elias, a post-doc at the Jenner, has just started a podcast series about the work the Institute does so if people want to learn more about vaccines against malaria and other diseases, they could listen to these:

I can’t end without mentioning my two favourite charities, the Schistosomiasis Control Initiative and the Against Malaria Foundation. They are both charities that focus on parasitic infections. Funding deworming and distributing bednets are the most cost-effective health interventions out there , according to charity evaluators Giving What We Can and GiveWell, so it is a shame that more people don’t know about them.

Anyway, thanks for producing such great podcasts and keep up the good work!


Geoffrey writes:


I believe that it was Dr. DesPommier who asked the question: how does the single eosinophil, which enters a body through GI tract, find its way to a single eosinophil, love, and progeny in lung tissue. He brought up issues of tracking down that eosinophil across many tissues and chemical gradients which are all appropriate but I think that he pondered the question in the wrong order (if I may be so nit-picky – even if that involves a different parasite). Rather, ask what chemical trails the eosinophil followed to end up in the same organ (if, indeed, it did), then what trails it followed to find a partner. It may be that the eosinophil’s sole goal is finding its mate but I suspect that its programming to find an appropriate growth environment (i.e., organ) is the primary programming. After all, what good does reproduction do if the parasite ends up in a hostile environment?

Thanks, again, for another interesting episode. It doesn’t hurt that romance and parasitism are usually good for attracting an audience.

QC Chemist

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