Case guesses:

Wink writes:

Dear TWIP Professors,

If you search The Text for cornea, you find Onchocerca, Trichinella and Thelazia. However, my guess will be different and I’ll probably be wrong, but I’ve gotten used to that. This case was from a while ago, and long ago I participated in some field clinics in Panama (when the Gorgas Course was given there). We often saw scabies, and in the San Blas Islands the mite burden was particularly high. I wonder if scabies can sometimes affect the cornea or if persons with heavy burdens of scabies will scratch their own cornea while relieving an itch near the eye. Love your whole podcast, every issue.

Wink Weinberg


Daniel writes:

Dear TWiPtomaniacs

Fresh from my randomly-generated victory 2 episodes ago, I’ll take another guess. In the unlikely event that I win another book, I’d like to donate a Spanish edition to the Hospitalito Atitlán in Guatemala (if they want or need it, otherwise please send it to the good cause of your choice). I had a great time volunteering there many years ago.

The fact that we have to go way back to the 90s makes me think we are dealing with a disease of historical interest in that part of Mexico. The combination of intense itch, subcutaneous nodules and punctate keratitis in someone living close by a river suggests the patient has onchocerciasis or river blindness. This neglected tropical disease is more commonly found in west and central Africa but there are foci in south and central America. The causative organism – Onchocerca volvulus –  is a filarial nematode transmitted by blackflies (Simulium spp.) which breed in fast-flowing rivers and streams. The symptoms are caused by an inflammatory response to larvae circulating in the subcutaneous tissue and in the eyes. Treatment is with ivermectin every 6-12 months. Ivermectin kills the larvae but not the adults, so needs to be taken for the lifespan of the adult worm (10-15 years). It is still a common cause of blindness.

After some googling I found that a focus of oncocerciasis transmission did exist in Oaxaca. It looks like it was eliminated by 2009, as part of an ongoing regional program of ivermectin mass treatment.

Best regards

Perryn writes:

Hello TWIP team!

I’ve been listening for at least a year, but have never worked up the courage to submit a case study response. Here goes my attempt….

The visual disturbances described in case study #143 initially brought a few possible parasites to mind. Ophthalmic cysticercosis (from T. solium) could cause visual disturbances, but does not explain the itching or the described “tender nodule”. Acanthamoeba keratitis could also be responsible for deteriorating vision, but again does not explain the itching or tender nodule. Additionally, the rare cases of this disease are generally associated with contact lense use, which was not mentioned in this case. Ocular larva migrans could explain the vision loss, but again does not explain the other symptoms, and is more common in younger patients. Onchocerciasis, caused by the filarial nematode Onchocerca volvulus fits all of the described signs and symptoms. Although now considered eliminated in Mexico (thanks to treatment of affected communities with ivermectin), it was known to exist in Oaxaca (the patients hometown) in the 90’s, and can persist for years in the host, meaning it could have been acquired years prior to the onset of symptoms.

The Simulium spp. blackfly is the intermediate host of this parasite. L3 larvae are spread from the blackfly to the human definitive host while the fly feeds. Inside the human host, the L3s develop to adults and form subcutaneous nodules, from which they release microfilariae for an extended period of time (years). The microfilariae hang out in skin, lymphatics, etc until they’re ingested by a blackfly. They penetrate the midgut, where they develop into L1 and through to L3 larvae, before migrating to the mouthparts, ready to infect another definitive host.

It sounds as though the disease is in its early stages, as there is only one onchocercomata (that we know of), and no other symptoms of microfilarial migration have occurred. Diagnosis can be made by observation of microfilariae from a skin snip. Treat with a single dose of ivermectin, to control migrating microfilariae. Because this doesn’t kill adult worms, surgical removal of the onchocercomata may be beneficial. If surgical removal is not performed, a repeat dose every 6 months for as long as the adult worms are producing microfilariae (which could be for years) would be required. Antibiotic treatment with doxyxyline may also be helpful, as Wolbachia are a known endosymbiont of O. volvulus, and seem to be required for a number of necessary parasite biological functions.

Thank you for all the work that you do – I’ve learned a lot from you!


(Guelph, Ontario, Canada)

Dave the Sheep Shearer writes:

Good doctors. It’s been a while since I submitted a guess but here goes. The young man from Mexico with eye and face problems. When I googled parasites eyes Mexico I got three possible choices. Toxocara however the worm heads for the back of the eye and the motile worm under the skin is a longer single worm.

The timing of this is important. The sixth edition says that Onchocerca volvulus was recently wiped out in Central America, however in the 1990s there may still have been cases in southern Mexico. It also says that in Africa the cutaneous form of the disease is usually on the lower parts of the body however in the Americas it is on the upper parts of the body. The description from the sixth edition looks very much like what was described. Now here is a novel approach. I would ask the patient if he had seen this before or knew what it was. If it is river blindness it’s likely that he has seen it before and knows or is familiar with it. I feel that asking a patient who has recently immigrated if they have seen this before can at the very least tell the Dr. how to approach the patient. In your case of the man from Africa with the ulcer on his ankle, asking him if he has seen this before or is familiar with it could tell the Dr. how to proceed. It’s a lot different breaking it to a born and bred New Yorker that they have a metre long worm in their leg that has to be slowly pulled out. However the man from Africa could be familiar with the procedure.

So there is my guess Onchocerca volvulus. The treatment mentions the use of Ivermectin in a single oral dose every six months for the lifespan for the adult worms which could be up to 17 years. It also mentions surgically removing the worms.

I wait with bated breath for your talk on Lyme. My symptoms go back 3 years and I was likely reinfected every spring as I worked my way through the Okanagan area of BC. shearing alpacas. I have been unable to work since April and have been through the roller coaster that is western medicine and Lyme.

Dave the sheep shearer from southern Alberta where it is -4c and calm.

Alijah writes:

Hey TWiPers,

This week’s case description initially really threw me off, but I think I have a good guess after looking into it a bit further.  So, the symptoms of this patient immediately made me think of onchocerciasis (AKA River Blindness).  Then, I thought back to the locational description though.  “Oaxaca?  Not Africa?”  After pulling up an epidemiological chart of the infection, I was met with more befuddling info – the infection seemed to indeed centralize in Sub-Saharan Africa.  It was only when I read the history of onchocerciasis that I found that Oaxaca and other south Mexican regions were once active foci for onchocerca volvulus infection.  Starting in 1992, however, the Onchocerciasis Elimination Program of the Americas (OEPA) sought to eliminate transmission in these areas.  Moreover, according to the World Health Organization, as of 2016, this program has succeeded in eliminating transmission in 11 out of the 13 original foci.  The two remaining regions lie within southern Venezuela and Northern Brazil respectively.

Now, with this knowledge in mind, since this case comes from the 1990s, Onchocerciasis becomes a legitimate diagnosis.  When an individual is infected with Onchocerca volvulus, the larvae begin migrating through the skin, eyes, and other organs.  As they die, they elicit strong immune responses that could explain the itching of the skin and the keratitis in this patient.  Additionally, if the worms reach adulthood, nodules can form around them – another symptom of this individual.  In order to get a more confident diagnosis, skin biopsies should be taken and examined under a microscope.  (I believe PCR and Immunofluorescence techniques are also available).

The treatment approach for onchocerciasis is a once or twice yearly dose of ivermectin for 10-15 years.  “Why so long??”  I asked myself after reading this.  Well, it turns out that ivermectin is able to robustly kill and prevent the release of the larval worms in these individuals, but the adult worms are simply paralyzed temporarily while existing in the nodules.  These adult worms then continue to live on and produce progeny despite the recurrent ivermectin doses; therefore, the lengthy treatment duration is warranted.



P.S.  Maybe I missed this announcement in an earlier episode, but was there mention of creating a This Week in Immunology podcast?  If so, neat!  Are there any updates on its progress?  If not, darn…  Thanks anyway, guys!

Melissa writes:

Hello TWIP-sters,

Woohoo!  Thank you so much!  I actually don’t have a copy of Parasitic Diseases.  I’ve been using the online PDF (which makes for searching for keywords easy).

I’m glad that EH&S doesn’t scare everyone.  I never dreaded when EH&S stopped by Dr. Pride’s lab (Actually, sometimes our lab auditor would stop by the lab to hang out, chat, and kill some time before his audit later in the same building.  That’s how we got the inside scoop of what was going to be rolling out soon so we could start taking inventory or get things queued up to get updated so we are in compliance.)

My guess for TWIP 143 is Onchocerca volvulus.  I actually skimmed through the Parasitic Diseases book and looked at the photos to see if there were any with an eye drawn or photographed.  According to Parasitic Diseases, to diagnose this, you need to get a skin snip from the area that is thought to have the highest concentration of microfilaria and put it in saline.  Within 10 minutes, it should be looked at under the microscope to see if there are any microfilaria.  The book also says that in Central America, the skin snip should be taken from the upper part of the body, which is consistent with where the patient is itchy. According to WHO, Onchocerca volvulus is transmitted by blackflies and blackflies breed in fast flowing rivers and streams.  The patient could have been infected when he was getting water for the family.  Parasitic Diseases says the treatment for this patient is ivermectin and with a single dose every 6 months, it can slow the progression of the ocular and cutaneous disease.

Thanks again!


Melissa Ly

Associate Biosafety Officer

University of California, San Diego

Allan writes:

Estimados Profesores TWIP,

Your case study of a patient in Mexico (in the 1990s) with tender nodules on the head, skin irritated from scratching and small punctate lesions on the cornea sounds almost unquestionably like onchocerciasis or river blindness caused by the parasitic worm Onchocerca volvulus. The scratching would be typical of the severe urticaria caused by the micro-filaria passing through the skin and the tender nodules would be typical of those called by adult worms. And of course this disease is still the second greatest cause of blindness worldwide. Confirmation could be made from finding micro-filaria in skin-snip biopsy or seeing them on a corneal examination, or excising a nodule finding adult worms. Treatment today is with ivermectin periodically until the adult worms die and some would recommend doxycycline to weaken the adult worms by killing their Wolbachia.  We frequently would see onchocerciasis in mountains of Guatemala and southern Mexico in the 1980s, but as of 2015 WHO had declared the region free of the disease.

Thank you for another great podcast.

Should I win the Parasitic Diseases 6th Ed., it will become a shared resource in the infectious disease sections of our Primary Health Care courses.


Allan Robbins, DIH, MPH

University of the Nations

Global Health Training

Kailua-Kona, HI 96740

Todd writes:

The unsolved case study for TWIP 143 is an aberrant nematode infection of Toxicara canis.  T. canis adults live in the small intestine of dogs and cats.  Eggs from the feces embryonate after 10-20 days in the soil.  If the embryonated eggs are injested by a suitable host, the larvae penetrate the intestinal tract and travel through the liver, bloodstream and lungs and are swallowed to mature into adult worms in the gut.  When the eggs are injested by man, the larvae hatch in the small intestine and penetrate the intestinal walls and wander throughout the body without completing their lifecycle.  The patient’s itching is most likely caused by a visceral larval migrans infection as the third stage larvae wander through the body and invade the tissues.  The most severe forms of infection involve the eyes and other organs such as the heart and brain.  Infection is most popular in children and adolescents under the age of 20.

Since T. canis eggs are not produced in humans a definitive diagnosis can be done by a histopath evaluation of infected excised tissue.  There is a less invasive ELISA using serum that detects antigens that are secreted by the second stage larvae.  Visceral T. canis infections can be treated with lbendazole or mebendazole.

Keep the interesting paper discussions and challenging case studies coming!


Peter writes:

Dear TWIP triptych,

I am postdoctoral fellow being mentored by Prof. Celia Holland in the Zoology Department at Trinity College Dublin, Ireland. When first hearing last week’s case study I first thought of ocular toxocariasis due to visual disturbance, itching and the presence of dogs. However, a quick consultation revealed nodules on head and punctate lesions did not sound right for toxocariasis. Then the symptom of itching so bad, that he could not sleep, brought a talk to mind that I was lucky enough to hear by Nobel Laureate Prof. William C. Campbell, just the previous week. Prof. Campbell spoke of itching so bad, that this symptom alone would warrant the need for a treatment. The itching was caused by the disease onchocerciasis also called river blindness, which would also explain the damage to the eye in the case study. I consulted Parasitic Diseases to confirm it and indeed nodules on the head were a symptom interestingly more associated with Central America than Africa, where the nodules are more often found on the lower part of the body due to differences in the vector behaviour and styles of clothing in the different areas. Punctate lesions were also more in keeping with onchocerciasis than my earlier diagnosis of toxocariasis. Finally as Prof. Campbell also showed a slide showing where onchocerciasis has been eradicated, I checked the information on Mexico. A WHO report dated October 14 2015 verified Mexico free of onchocerciasis, so the earlier date of the case being in the 1990’s confirms travel history in an endemic area. So my diagnosis is onchocerciasis, as a result of infection with Onchocera volvulus (Leuckart 1893) via the black fly vector Simulium spp. Definitive diagnosis by examining a skin snip and long term treatment with Ivermectin at least every 6 months.

I hope I am correct but after hearing Dickson saying not to remove his error from the last episode, I am not so fearful to put my attempt forward. Really enjoyed hearing Dickson say to not to edit it out, it takes someone very secure in themselves to allow it to be shown that infallibility is not a requisite to being a successful scientist. Very comforting for an early stage scientist like myself to hear.

Prof. Campbell took part in many functions while in Ireland but one was an informal talk with TCD Zoology undergraduate and PhD students and postdocs on his life in science in art, that left us all inspired and driven to bravely pursue our curiosity without fear and to persevere. He also gave an equally inspiring discourse lecture at the Royal Irish Academy where among many things he championed random empirical screening and hopefully helped me solve this week’s TWIP case study. Prof. Celia Holland gave a compelling response to Prof. Campbell’s discourse, using Prof. Campbell’s journey in science to highlight the importance of mentorship for young scientists, the challenge of tackling neglected tropical diseases, the need for funding not only at an international but also at a national level to tackle NTDS and finally what an amazing world parasitology is to introduce young people into. On that note I would like to thank you all for your work on the podcasts. My bachelor degree is in Applied Ecology but my postgraduate and postdoc work has been on parasitology in wild mammals and I find the podcast excellent for exposing me to new aspects of parasitology, particularly clinical parasitology in humans. I also have recently moved into the field of eco-immunolgy so benefit from TWIM, TWIV and the IMMUNE podcasts now also. I was lucky enough to be asked to drive Prof. Campbell around and he was kind enough to sign my copy of “Trichinella and Trichinosis”. Who doesn’t love a book with the line “Herbst was in the habit of dissecting various animals and feeding the remains to his pet badger”. Through the book Dickson came up and when Prof. Campbell asked did I know him, I had to confess only in the way you sometimes feel you know somebody who has never met you, when you have listened to them talking a lot on the radio through the podcasts.

Apologies the email is so long. From Dublin, Ireland where in keeping with the season, the wind goes right through you. Temperatures 3-4 degrees, gusty north west winds.

All the best

Peter Stuart

Trinity College Dublin, the University of Dublin

Chris writes:

Dear TWiPsters,

It’s wet and just above freezing in Athens, GA, but amazingly there’s also a chance of snow. We may yet get a dusting before the year is out.

This case of the boy suffering itching and visual disturbances brings to mind a few different parasites. Zoonotic infection can sometimes produce these symptoms: Toxocara larvae can migrate to the eye, although typically not the cornea. Cysticercosis can produce sensitive subcutaneous nodules and also affect the eye, though the presentation is unlikely to be the punctate lesions described.

The most likely cause of these symptoms, however, is Onchocerca volvulus, which is endemic in Oaxaca. One report puts a half-million people at risk of infection in the Americas. The patient’s need to collect river water exposes him to the habitat of the blackfly vector, and the ocular involvement is characteristic of River Blindness. Mass drug administration has been conducted in Mexico since the ’90s, so hopefully the risk is substantially less than when this patient was seen.

The ideal means of diagnosis is observation of microfilariae in a skin snip. Adult worms can potentially be obtained from biopsy of the skin nodules. A sensitive but nonspecific filarial antigen test can also be performed. The current recommended treatment is ivermectin and doxycycline. Ivermectin should have been available by the time this case was handled, and is much preferable to DEC, which can cause serious side effects.

As always, thanks for the very interesting case, and the reminder that these parasites still exist close to home.

regular email

Andrew writes:

Hello Fellow Parasitologists!

I must say… I am hooked on your podcasts. The level of knowledge that you bring to all these organisms in which I studied in college and work with almost everyday is tremendous.

I am a Medical Technologist in a large clinical diagnostic Microbiology lab in Boston, MA. My main areas of interest are in Parasitology, Bacteriology, and Mycobacteriology. I would be the guy in the Parasitology Lab who would be identifying this worm for the doctor, so I figured I would give this a shot. I love my job – it’s always fun because every day brings something new and unexpected. I am the guy at the microscope- not at the patient’s bedside- so, I don’t see the clinical manifestation side too often, so please excuse me if I am incorrect on some counts here.

I believe the organism described in the podcast is none other than the human whipworm, Trichuris trichiura. Due to the shape and size of the adult worm, the description matches this organism. Whipworms are funny little guys. First off, they are shaped like Indiana Jones’ whip; a thick end with a long thin, tapered end. That’s how they get their nickname. A lot of people actually think the skinny end is the tail, when in fact, the skinny end is the head. Most parasitic worms don’t really get out of the house much, they just eat and lay eggs- Trichuris trichiura is no different. It uses its head to thread itself inside the mucosa of the large intestine and then the “fatter” side is basically an egg factory, which (according to the CDC) can produce up to 20,000 ova per day. The ova of this organism are very unique under a microscope, and this is usually how we make the diagnosis here in the lab. The eggs look like mini footballs that have mucoid polar plugs at both ends. These mucoid plugs are where the larvae will emerge from when they hatch. We do also sometimes get the adult worm in the lab and it’s amazing to see how something so unique can be living inside you. I have also seen a co-infection with Ascaris lumbricoides quite often. These two worms are transmitted in a similar manner and in the same environments so it makes sense.

In a lot of cases, the worms cause dysentery and iron deficiency anemia due to the traumatic damage caused to the mucosa. The anemia can be quite severe if the infection is heavy enough. According to, The worms digging into the mucosa of the large intestine will usually trigger a severe immune response in the large intestine and may sometimes give the host the feeling that they need to defecate, when they don’t. I am not quite sure about eosinophilia being present during infection, however, I would assume it would be as it is a parasitic infection that triggers an immune response.

Trichuris trichiura, like I said above is found almost everywhere Ascaris lumbricoides is found. It is found worldwide and likes warm and temperate environments and is most successful in areas with poor sanitation as it is spread by ingestion of human feces. I will usually see it in patients from the warmer and tropical regions of Asia (like Philippines and India), Caribbean Islands and Africa. I was surprised to find out from the CDC, however, that it can be found in the southern part of the United States.

Thanks for making me do some research to discover some new things, I always appreciate learning. Keep up the great work with the podcasts and I promise I’ll keep listening!

Your friend,

Andrew Berens, MLS(ASCP)

Boston, MA

Chris writes:

Dear TWiPsters,

It’s a sunny 56F (13C) in Athens, GA, and the chance of snow is still far, far away. (Yes, we do get snow some years)

The description of the 4.5cm worm recovered from this patient immediately brings to mind Trichuris trichiura, the human whipworm. The long, slender anterior end is very distinctive for the adult stage of this parasite, but the football-shaped eggs with double opercula are equally distinctive. It does still occur in the United States, especially in the rural southeast, so international travel is not required. There is also the rare possibility of a zoonotic infection with T. vulpis or T. suis, parasites of canids and pigs, respectively. In any case, transmission is by the consumption of contaminated food or water. The eggs require two weeks of development in the environment, so autoinfection is unlikely. Treatment may be with a three-day regimen of mebendazole, albendazole or oxantel.

Eosinophilia is not typically associated with whipworm infection alone, and anemia is only expected with very high worm burden. Assuming prior exposure to fecal contamination, the patient should be examined for other parasites that could account for these findings.

Assuming you’re still giving them away, here’s to the off chance of adding a new parasitology textbook to my shelf and rousing the envy of my coworkers!

Trudy writes:

Dear TWiPpers,

I have a question relating to parasite exposure dosage.  When it comes to other microbes, such as bacteria for example, I usually think that the likelihood of someone developing symptoms of infection depend on the amount of the microbe the person has been exposed to.  I think that this is generally also the theory behind washing produce – you will never get rid of all the dirt, soil, or poop, but the idea is to get rid of most of it, so you don’t get sick.

So my question is, can washing produce help us prevent infections with parasite embryos as well?  I think it’s interesting that the lady in TWiP 142 developed symptoms from having just one worm.  Is that all it takes for some parasites?  On the other hand, it seems to me that it was unclear whether the anemia was related to the whipworm infection.  

Please clarify, if possible.

Thank you!


P.S. I’m always looking for any excuse to visit NYC, so I would love to be an in studio guest on TWiP, are you kidding me?  I also have a book for Dickson to sign… last time I was in the studio I had not yet read West Nile story, even though I have a PhD on the topic AND I am a huge fan of Dickson Despommier.  Oh, the shame!  This has since been corrected and I am looking forward to my next opportunity to meet Dickson.

Sara writes:

Greetings esteemed triple TWIP doctors!

I write to you from an uncommonly sunny Glasgow, Scotland (10 degrees C). First email to TWIP (my favourite podcast for years now!) and I’d like to express my sincerest thanks for keeping it up and always being so edutaining. I love the introduction of Daniel and his case studies – I’ve been guessing silently from the start but I’ll make an effort to start sending in guesses from now on. I also really like Dickson’s little “Heroes/Profiles etc of Parasitism” segments and I thought I’d send some cool links and a suggestion in relation to them. I’ve just become the Chapter Lead for ScienceGrrl Glasgow (a group of Scotland-based science communicating gals, guys and babies) and over the past year we have introduced a new activity that we take with us to events like science festivals, schools, care homes etc. It’s called Unsung Heroines and we have centered it around Youyou Tu – check out the links below to our blogs on the subject to learn more about her and her important achievements – and other female scientists that have made important and sometimes not well known contributions to science. A bit self-serving, but I thought I’d try for a TWIP-bump! Anyways, it would be cool if Dickson made one (or more!) of his little segments about a female scientist working with parasites – I’m sure there are some and I’d love to know more!

Huge thanks from myself and ScienceGrrl for your science communication efforts and a possible TWIP-bump, and if I don’t get a guess in before Christmas I’ll send my season science greetings via our #elfonascienceshelf now:

Dec 1st in our ScienceGrrl Glasgow Twitter advent calendar:

Happy holidays!


Anthony writes:

I was thinking about Trichuris transmission,  Dogs defecate most anywhere and mouth/chew/swallow most anything.  How they can catch whipworm is clear.  With the use of night soil and contamination of vegetables, it’s easy to see how people become infected.  With cats, it’s not obvious.  Cats defecate in particular spots.  How they would consume dirt from there is not easy to see.  Do mice digging up and consuming cat feces serve as fomites?  Or, might there be vertical transmission / spread?

# # #

I came across this Site:

If you think that it looks good, perhaps it might rate a mention.


Anthony writes:

Perhaps there might be a feature on parasites that are not.  Here’s one:

A dentist once told me that the root canal procedure was developed in the belief that the nerve was a worm:

The existence of tooth worms was not disproven until the 18th Century