Anthony writes:

The symptoms are a bit vague but I feel like the geography matches up with Gnathostoma spinigerum 

These worms seem to just wander around the human body as humans are a dead end host.

The CDC recommends if the patient is not that ill that they get ivermectin 200 micrograms/kilogram orally in the morning or night for two consecutive mornings or nights.

I have been starting my CPHT internship and have been filling prescriptions – so far nothing parasitic but quite a lot of thrush cases needing fluconazole. 

Hope Dickson comes back soon!


Alexander writes:

Dear Professors,

First and foremost, I want to wish Prof. Despommiers a speedy recovery and good health! With any luck, he might now be reading this letter himself or have it read to him, fully restored and healthy again.

On to the case: The history of ingestions of incompletely cooked fish in southeast asia, the wandering edema and the blood eosinophilia are all consistent with gnathostomiasis. The larvae are acquired by ingesting raw fish, most commonly eel in thailand, and the third-stage larvae travel throughout the body, unable to complete their life cycle in humans by returning to the GI tract; therefore, no eggs would be found on stool examination.

As the diagnosis can be made by tissue staining in this case, serologic testing might be omitted in favour of early treatment. Albendazole 400mg bid for 21 days seems to be the standard, although ivermectin is an alternative. Thanks for the great case, I’m anxious to hear the next one! Best regards,


Andrew writes:

Kia ora from Pongaroa,

No Book won yet but I would prefer to hear another one of Kevin’s amazing emails to be frank.

My guess for the 30 year old woman with swellings under the skin is Gnathostoma spinigerum.

My PDF-PD7 tells me that exposure is through infected fish, snakes and birds. Our patient is an adventurous eater and has been in South East Asia where the parasite is commonly diagnosed.

Humans are not a definitive host so the lava will not mature but they can cause damage, especially in the nervous system. After ingestion the lava migrate through the stomach wall and, apart from some tiredness and diarrhea, this stage is fairly asymptomatic. Once the lava have migrated to the skin, subcutaneous swellings appear.

Treatment: Albendazole or Ivermectin.

Hoping that this will be read out in the No-BS Level Incubator.


Gabriel writes:

Hello from Baja California.

Cutaneous Gnatosthomiasis, caused by Gnathostoma sp. is suspected by intermittent subcutaneous or cutaneous migratory swelling, elevated blood eosinophils, and relevant exposure. Confirmed by biopsy and microscopy. The loose stools and itching can be symptoms of the larva’s intestinal and cutaneous phases respectively. The tingling sensation on the fingers has been known to happen when inflammation during a round worm infection causes median nerve compression.

Identification of the larva species can be performed by differentiating microscopic characteristics at an anatomical, cellular or tissue level. DNA and other molecular tests can also distinguish amongst the four or five species known to infect humans.

I’d bet on G. spinigerum, endemic in Thailand and also found in Indonesia. The patient was most likely infected by sampling local cuisine containing raw to undercooked infected meat from fish, frogs, snakes, birds and other animals. A salad with a piece of infected snail could also do it.

Thank You    Gabriel

Martha writes:

Dear TWiP team, 

     I hope this finds you all well. Since I won a book already, don’t enter me in the drawing, however I intend to continue to respond to these cases.

     I am happy to report that I have no personal experience with this month’s parasite. The patient presented with swellings on different parts of the body. History significant for travel to southeast Asia and eating the local cuisine, including uncooked freshwater fish. On blood work the eosinophils are elevated and a biopsy from one of the lesions suggests an immature nematode.

The CDC has a helpful page on Gnathostoma spinigerum:

G. spinigerum seems to fit all the features mentioned. This is another case of humans not being a usual or functional  part of this creature’s life cycle. We humans get involved when we eat the second intermediate hosts (fish, eels, frogs) or one of the paratenic* hosts (birds, snakes, lizards). The larva is not able to complete its maturation in humans, so humans do not transmit this parasite. 

This is treatable by a three week course of albendazole or a one or two day course of ivermectin. This is preventable by cooking fish to 145F (63C) which kills the parasite, or freezing to -31F (-35C). 

best wishes, Martha


* I learned a new term: paratenic host-an organism that harbors the sexually immature parasite but is not necessary for the parasite’s development cycle to progress.


Sherrill writes:

Vincent, Daniel, Dickson et al.,

Here we have a young woman with a history of travel in SE Asia who is an adventurous eater. She Presents with arm swelling. Loose stools initially resolved. Eosinophilic. Biopsy shows larval nematode. 

My first thought was that maybe she tried the “jumping salad” in Thailand– featuring delectable live “raw” crustaceans, minnows, or crab eggs? I,e., Nematode Capillaria Philippinensis. 

But wait a minute-symptoms for infection with said jumping salad a la nematode would have been vomiting and continuous —protracted —diarrhea.  

This is not our case.  

Next I wondered …..could this be Loiasis? The infamous eye worm?  A possibility perhaps. Filarial nematode inducing calabar swellings, that is, itchy swellings on the body.  We have no report of itching in the subject case. But what about that swollen arm full of nemadodians?? 

Loasis is vector borne by Deer Fly bite. Our case hint suggests we need a food borne parasite.   Loasis is found in Africa. Wrong area of the planet. We need a SE Asia endemicity parasite.  So have to reject the Loasis Nematode idea as well.

Third guess: Cutaneous Gnathostomiasis?
Eosinophilic? Check.
Intermittent migratory swellings on torso or upper limbs? Check! 
Nematode? Check!
Food borne? Yes! Can get it from raw or undercooked meat—dishes with raw fish like sushi and ceviche. Or even snake, duck or frog!
Endemic where?  Japan, Thailand, Vietnam, Mexico. SE Asia. 

Bingo. This has got to be it! 

Very interesting emerging zoonosis.

Am including the CDC link:

Thank you so much Vincent, Daniel & Dickson. Others have thanked you far better than I……and I agree with all the kind, witty, smart, learned, erudite & heartfelt appreciation expressed by so many. 

Thank you guys for being my “science friends”.  

Stick shift always a must for me too btw Vincent. 



Lawrence writes:

More of a googling-cap than a thinking-cap. A search for nematode  parasite fish human swelling thailand indonesia resulted in several  candidates, but the best fit by far was:

 Gnathostoma     It ticks all the boxes including possible loose stools early on, elevated eosinophils and no onward transmission (due to not being able to complete its life cycle in humans. 

 Treatable with albendazole and, if the covid-vaccine-hesitant haven’t already bought up all the stocks,  ivermectin.

Katy-Jane writes:

Hi all,

In my (completely non-medical opinion), we are dealing with two different things here. The loose stools are potentially caused by the woman’s adventurous fishy diet, but do not seem to be causing her much concern. I’m going to guess that they are a “red herring,” and unrelated to the eosinophilia and tingling sensations described. I’m not sure if the tingling in her fingers was bilateral, but I’m going to guess that it’s caused by nerve compression of the nematode larva, which was found on biopsy. 

The nematode larva could be of the soil-borne species, but larvae of these species tend to invade more through the feet. I’m going to guess at a mosquito-borne Difilaria species, which would be more likely on the arm…although presumably humans are aberrant hosts for these little critters. If this is the case, this woman’s travels are not the problem, as this problem could have been picked up at home.

All a complete guess, so I apologize for the rushed email – I really hope I get it in on time! 

Katy-Jane Shanak
(Now full-time!) Faculty in Veterinary Technology & Dairy Sciences
Northcentral Technical College
Wausau, WI

Schuyler writes:

Good morning from the unpleasantly warm nation’s capital, Washington, DC. 

I admit, I have been a major slacker and have not written in since Spring. But with the third semester of medical school beginning, I am hoping to jump back on the TWiP bandwagon and maybe win that book. Hopefully I am sending this is time to make it into the episode. We have a patient with changing swellings in her arm, known to be caused by some larval nematode, after returning from travels to Thailand and Indonesia. Big hint in the episode seemed to be the importance of the patient eating raw or pickled freshwater fish. 

According to Liu and colleagues (2020), gnathostomiasis, caused by various Gnathostoma species, is a food-borne illness seen in Thailand  It is caused by the consumption of raw freshwater fish or other animals contaminated with larvae and is characterized by “migratory cutaneous swellings and eosinophilia.” The paper is an interesting review of the disease and describes it as an emerging global disease as cases are rising due, in part, to adventurous eating. 


I’d like to give a more extensive differential but I need to get this in before the next episode and I need to go prepare for anatomy lab. 

Wishing you the best,


9 Sergio writes:

Hi all at TWIP,

Case Study 196 Gnathostomiasis (Gnathostoma Infection)

I think she was infected with Gnathostoma, because she ate pickled fish, that’s the type of food (animal) this parasite likes to reside in.

Once ingested, after 2 or 3 weeks it travels through the stomach wall  and reaches the skin causing the swellings.

I hope none reached her brain or eyes.

Thanks for all your hard work, love you all from microbe tv.

Sincerely Sergio

PS: I hope to visit the incubator one day, once it is open.

Elise writes:

Dear TWiP Trifecta, 

I very much hope this finds you all well. I am writing to you from an extremely warm and humid Lower Manhattan where it is 93 degrees F (34 C) and my phone has been alerting me with warnings about excessive heat, air quality and whatnot. 

Before I attempt a diagnosis, I wanted to tell Vincent about a local group that does whale watching (which is something he was talking about on a comparatively recent episode of TWiV). The Gotham Whale folks do research and take people out on whale watching excursions. Here is their website: 

So, I am as usual unsure of my diagnosis because Dr. Griffin said this was a challenging diagnosis and I’m not super secure with my assessment. I suspect that the adventurous eater with the peculiar swellings and  larval nematode may have a Gnathostomiasis infection. 

Gnathostomiasis is common in Indonesia and Thailand (and also in the Americas) and is easily acquired by eating raw or undercooked fish (though it is present in other protein sources as well).  An infection is usually characterized by elevated eosinophils, though this is not necessary for a diagnosis. While the young woman’s early symptoms (loose stools, tingling fingers, are symptoms of other infections, the random-seeming swellings that appear, recede and recur elsewhere are characteristic of a Gnathostomiasis infection. (According to one source, undercooked Asian swamp eels are a particular source of Gnathostomiasis in Thailand and Vietnam.)

Depending on where the nematode takes up residence in the body, the infection can be more or less severe and dangerous and can cause encephalitis or meningitis. Since one of the swellings on the woman’s body was biopsied, it should be easy to diagnose. 

The remedy for this infection is a course of albendazole or ivermectin (quite a long course—21 days) and surgical removal of the larvae. If this diagnosis is correct, how would the removal of the larvae work for the patient since the swellings have come and gone?

As always, thank you so much for everything all of you do. I am so grateful to all of you for your work, your humor, your interests and for sharing them. 

Many best wishes

Elise in Lower Manhattan