Case guesses:

Mike in Oregon writes:

Hello gentlemen,

My guess for case 144 is Anisakiasis..Since I am not a doctor or even close, I will quote the CDC.

Anisakiasis, or herring worm disease, is a parasitic disease caused by nematodes (worms) that attach to the wall of the esophagus, stomach, or intestine. The best ways to prevent this disease is to avoid eating raw or undercooked fish or squid.

When certain infected marine mammals (such as whales or sea lions) defecate into the sea, eggs are released and become infective larvae while in the water. These larvae are ingested by crustaceans, which are then eaten by fish or squid. When humans eat raw or undercooked infected fish or squid, they ingest nematode larvae. Once inside the human body, the larvae can invade the gastrointestinal tract. Eventually, the parasite dies and produces an inflamed mass in the esophagus, stomach, or intestine.

Some people experience a tingling sensation after or while eating raw or undercooked fish or squid. This is actually the worm moving in the mouth or throat. These people can often extract the worm manually from their mouth or cough up the worm and prevent infection. Also, some people experience vomiting as a symptom and this can often expel the worm from the body. The worms can only be removed by special tweezers that you con can only get from me at the special low price of $749.99. Did I say special? Hurry now. Did I say NOW?!!

Sorry, couldn’t help myself. Just trying to make a living like all the other slackers out there.

Thought you might like this. “The Origin of the Mosquito” I enjoyed this story as told in the podcast:  ‘Arthro-pod episode#35’ ..Also found at..

Mike in Oregon

Iosif writes:

Dear Twip Team,

I apologize for my lack of participation these last few episodes. It’s been interview season and it isn’t always easy to find free time.

For my differential for this case I’ve come down with two different ideas which differ based upon what in particular this man is feeling in his legs.

If he is feeling some numbness or an electrical sensation then I am tempted to say that he may have a B12 deficiency and there is some abnormality with his Dorsal Column Medial Lemniscus pathway. If a parasite is causing this, then I would have to go with Diphyllobothrium latum as my diagnosis. This parasite absorbs the B12 that the host consumes and thus may prevent you from getting enough B12 to use for DNA and amino acid synthesis. It is also carried by fish such as the salmon that this gentleman consumed. I would still ask the patient for other reasons why his DCML could be damaged such as sexual activity (syphilis), drug use (nitrous oxide use), and diet (for B12, vitamin E or copper deficiency). Maybe a CBC is warranted to look for the megaloblastic anemia?

The other idea I had was if the patient’s legs felt restless. Iron deficiency can sometimes lead to an exacerbation of restless leg syndrome and a hookworm infection could be the culprit. I think that this is less likely since I didn’t hear of any risk factors for a hookworm infection, but more information could still be elicited. If the CBC shows microcytic anemia then that could point to something causing iron deficiency.


Iosif Davidov

P.S. I would love to visit you guys if you’re ever recording in the city, but I will be gone come mid-January to my rotation in Uganda

P.P.S: Since I have your textbook. I feel it would be more fair for someone else to win.

David writes:

Dear Hosts,

I was surprised to hear the culprit on last week’s episode of TWiP was the nefarious Onchocerca volvulus. I thought of this parasite after hearing the case and was skeptical as the case occurred in Mexico, but I was equally surprised to hear that river blindness was eradicated from the region recently – a pleasant bit of information!

As for the case in episode 144, I narrowed my choices down to two parasitic worms found in salmon: Anisakis simplex and Diphyllobothrium latum. Both of these parasites have been featured on previous episodes of TWiP, and both are immediate red flags when it comes to fish parasites. Upon reviewing the life cycles of these two worms, I recalled that Anisakis worms would not pass out in the stool as motile objects – rather they would remain inside the host and pass their eggs in the feces. D. latum, however, should have motile proglottids as a cestode. I discovered a website which claims “ultimate gravid proglottids are not ‘shed’ in the feces as actively motile sacks of eggs”, but instead “detach from the strobila and are shed as strands of variable length”.

Seeing as this speaks to the length, but not the potential for motility, I will guess that the man contracted D. latum from improperly prepared salmon. It is possible that the fish was not frozen or heated to the proper temperature to sufficiently kill the worms. While this parasite typically infects freshwater fish, the Sixth Edition of Parasitic Diseases notes that cases of Pacific salmon (which match the Vancouver locale of our patient) spend a portion of their life cycle in freshwater, so the unfortunate patient may have eaten infected salmon. Here’s a fun set of safety notes on how to avoid contracting fish parasites: (

Thank you once again for the informative and entertaining podcast.


David Pirovich

PhD Student, Molecular Helminthology Lab at Tufts Cummings School of Veterinary Medicine.

Theodore writes:

Dear TWIP,

I am a longtime listener of of TWiV, having discovered it while working on a research project involving Moloney-Murine Leukemia virus detection in breastmilk as a model for HIV vertical transmission. I only recently began listening to TWiP and I regret not finding it sooner, as an interest in parasites is one of the reasons I began the long path towards becoming an infectious disease specialist.

The diagnosis in your presented case is most likely a tapeworm of the Diphyllobothrium species, whose larvae were likely ingested in the marinated or under-cooked salmon the man had been eating. Unique to this tapeworm, as many medical students can tell you, is its affinity for absorbing the vitamin B12. B12 deficiency is a cause of megaloblastic anemia and is associated with peripheral neuropathies. The “funny feeling” in the man’s legs is likely a parasthesia or numbness related to his B12 deficiency! He should receive a dose of praziquantel (5-10 mg/kg) and B12 supplementation, with follow up to make sure his neuropathy is not worsening.

Hopefully I can still be in the running for a copy of Parasites (6th edition)! Will there be a signature from Dr. Hotez as well? He is something of a personal hero of mine for his work on NTDs and vaccine advocacy.

As for me, I am an MS4 at the University of Toledo College of Medicine applying for residency in Internal medicine, and I hope to be an Epidemic Intelligence Service fellow before pursuing training as an Infectious disease specialist.



Theodore S. Rader IV, MS

University of Toledo

MD Candidate 2018

Evelin writes:


Here is my answer for the TWIP (This Week in Parasitism) case study as mentioned in episode 144.

Case Study:

Individual in 30s, male, presented to physician with stomach upset, uncomfortable feeling in legs. Has motile objects in stools. From Vancouver BC, was eating salmon, reports was either dried/smoked or marinated. Not sure if this is relevant. Brought motile objects to physician.

Parasitic causes of upset stomach following the consumption of raw Pacific salmon include anisakine nematode larvae or Diphyllobothrium spp. (broad fish tapeworms). Both are commonly found in several species of Pacific salmon, including sockeye salmon (Oncorhynchus nerka). Although it is possible that anisakine nematodes could cause stomach upset as the larvae burrow into the gastric mucosa, the finding of moving objects in the stool strongly suggests this is an infection with a cestode belonging to the genus Diphyllobothrium.

The life cycle of this cestode involves two intermediate hosts; the first is a copepod and the second is a fish. Other predatory fish can act as additional paratenic hosts. The definitive hosts are fish eating vertebrates such as birds, dogs, bears and foxes, and, obviously, humans as demonstrated by the case. The individual acquired the infection by ingesting plerocercoid larval forms in the flesh of the undercooked (smoked) or raw (dill marinated) fish.  The infected male patient then acted as the final host. Diphyllobothrium spp. compete with the host for vitamin B12 in the diet; vitamin B12 deficiency could explain at least some of the reported symptoms including digestive issues and creepy feeling (tingling?) in his legs.  The motile objects found in the stool of the patient would be the gravid segments liberated from the mature strobila found in the small intestine.

This case is certainly an infection with a Diphyllobothrium spp., but which one?  Most early reports of human infections in North America concluded that Diphyllobothrium latum was the causative agent but there are a number of less commonly reported species that can infect humans.

One of these, Diphyllobothrium nihonkaiense, was commonly reported from Pacific salmon in Japan and Korea but had not been reported from the Pacific coast of North America prior to the infection reported in the present case. This tourist-acquired infection with Diphyllobothrium nihonkaiense through ingestion of raw/undercooked Pacific salmon. In the case report of this infection (Wicht et al., 2008), confirmation of the identity of the causative agent as Diphyllobothrium nihonkaiense was made using sequence-based genotyping (DNA barcoding) at two genetic loci (18S rDNA and mtCOI). Finally, dimensions of the eggs found in the mature proglottids recovered from the stool were too small to be Diphyllobothrium latum but matched eggs from Diphyllobothrium nihonkaiense.

Evelin Rejman


MSc Student

Department of Pathobiology

University of Guelph

Alan writes:

Estimados Profesores TWIP,

The weather here in Honduras is clear and 34ºC, and I hate the thought of giving up ceviche but this week’s episode has made me at least “think” about it.

My first check online surprised me that people now are contracting anisakiasis from Salmon in Canada, which I had thought only happened in Japan.

But on reflection, while a living worm from anisakiasis might be visible if vomited, it should never be seen in the stool as as they typically die in humans.

The usual “motile objects” my patients have reported in their stool over the years have been ascaris and tapeworm proglottids.

The uncomfortable feeling in the legs I hope is a red herring, like “Doc, when I scratch my knees, my teeth itch.”

I would most suspect a tapeworm.  D. latum or D. nihonkaiensein in this case, but look forward to hearing the conclusion of the case.

Still hoping to win a signed copy of Parasitic Diseases 6th Ed.

Great article discussion and case study.



Kona, Hawaii, temporarily in Honduras

Allan Robbins, DIH, MPH

University of the Nations

Global Health Training

Kailua-Kona, HI 96740

Gavin writes:

Dear TWIP Team,

I think I’m cutting this one a little close, so I have to rush out my case guess for TWIP 144. There are plenty of parasites from undercooked salmon that cause abdominal pain. However, due to the motile objects in stool, my guess is a fish tapeworm in the genus Diphyllobothrium. The leg pain could potentially be explained by vitamin B12 depletion. Anisakis and Giardia can also be obtained from undercooked salmon, and this person may have a coinfection since fish tapeworms are often asymptomatic. An interesting possibility would be Nanophyetus salmincola since there wasn’t much in the literature on this one infecting humans. Diagnosis could be made via the motile objects in hand as well as stool O&P. Treatment with Praziquantel will probably work.

Hope your 2018 is off to a great start!!!

UCSF School of Medicine
Class of 2021

Trudy writes:

Dear TWiPpers,

I’m not sure whether to laugh or cry at the attached article, which discusses a new “health” trend featuring raw water. Yes, RAW. WATER. I know this is a family friendly show, but WTF!! Are people really this stupid? I guess these are also the same people who consume raw milk and refuse to vaccinate their children. To quote Mark Crislip, “the cow’s udder is south of the anus”.

I know I’m preaching at the choir here, but besides the possible presence of arsenic, uranium, bacteria, and parasites in raw water sources, this water also does not contain fluoride. Do schools no longer teach history? Otherwise, why would people forget why our drinking water is treated and fluoridated? As one who grew up in Eastern Europe without fluoridated water, I can tell you that my dental issues continue to break the bank to this day, despite the fact that I do and always have, practiced excellent oral hygiene.

Anyway, I hope this trend dies out quickly. Happy New Year!

Andrea writes:

Hello Twipitos!

I thought this couldn’t possibly be true. Have you heard about “raw water”?:

So much for 2018…..

Thanks as always for this and all of the other podcasts.

44F and raining, of course, in Seattle.

Johnye writes:

Good morning from 13 Celsius Boston.

Please ask Dr. Griffin to listen to his statement at about 40:17 to 40;20 minutes. He made, perhaps, a Freudian slip when he referred to DEC, diethycarbamazine, as DIC, disseminated intravascular coagulation. I don’t think that is what he meant, As I recall, hypotension can occur when DIC is present, but that is now beyond my scope of practice.

As usual, most impressed by the medical students’ differentials and thoughtful presentations. They are inspiring!

As the season approaches, thankful for the wonderful worlds of microbiology that are made accessible, presented, explored and explained.

Best of health to all!

Magnolia publishing writes:

The current arthropod podcast is about parasitic insects, TWIP listeners may enjoy it also:

Daniel writes:

I just heard about this podcast. It is really interesting, and a good alternative to getting worked up over politics.

There was a matter brought up several times during this series: Some parasites do not have aging genes, and can be serially passed through different hosts without senescence. I am a fan of the Star Trek series, and there is one character who seems to reflect this phenomenon. A character named “Dax” is a member of a species of aliens that act as hosts to an internal symbiote. The symbiote is like a large worm, and is serially passed from one individual to another, allowing it to live for centuries. As it does, it conveys the memories and personality traits of the previous hosts to the new one, with associated changes in personality and acquisition of knowledge and skills. To be chosen as a host is therefore considered an honor.

I thought you might find this interesting. I am sure that the fictional arrangement described was created coincidentally, without knowledge of the apparent immortality of real parasites.

Desperate writes:

I got it from my daughter who is an 8 year old twin. I’ve had it for over a month. I just listened to both of your podcasts about Pinworm and so far you are the only people that have given me any good information on the topic. I’m extremely frustrated and unable to beat this. I can’t eat, sleep, blood pressure is up, weight is down. By the way I also contracted Lyme in July and Took antibiotics for it. I have the pinworms in other locations too (nose, ears, etc). I’m not crazy (even though a lot of people are making me feel like I am!). I would be willing to share my story with you (not using my name), and also any advice you might have or light you could shed would be life saving. 🙏🏻 I am in New York City under the care of some of the best doctors but I need some advice, guidance, recommendations for hospitals, doctors, herbalists, dietary and lifestyle recommendations.