Points about pharm:
Nematode infections on USMLE are basically always treated with -bendazoles (i.e., mebendazole, albendazole, etc.). These are microtubule inhibitors. Don’t confuse with -azoles (antifungals).
Pyrantel pamoate is another agent that can be used for nematodes, but lower yield. Diethylcarbamazine is non-existent.
Ivermectin is an odd-one out used for Onchocerca volvulus (discussed below).
Praziquantel is used for cestodes and trematodes. This causes worm paralysis.
In short, mebendazole and praziquantel are the two highest yield anti-helminth agents for USMLE.
It is extremely rare USMLE lists more than one anti-helminthic agent as answers to a question. Usually the Q is very easy, where the answer is the only anti-helminthic listed. But there are a couple questions out there where they list a -bendazole and praziquantel side by side. So you must know that mebendazole is used for nematodes; praziquantel is used for cestodes and trematodes.
HY point about bloods:
Eosinophils can classically be elevated in helminth infections. This is because eosinophils play a role in killing helminths via release of major basic protein. Normally eosinophils should be <5%. In helminth infections, they can be >6-8%. Questions where eosinophils are, e.g., 15-20% would be considered flamingly obvious and pass-level.
Eosinophils can occasionally be elevated in fungal infections as well, so don’t be confused by this. In other words, although eosinophilia is classically associated with helminth infections, just be aware this is not 100% specific and it can occasionally be seen with fungal infections too.
For the following helminths, the USMLE can give a vignette where you are easily able to diagnose the organism, but then they ask how it’s acquired, where they have answers such as “ingestion of fecal-contaminated soil,” “through the feet,” “mosquito bite,” “fly bite,” etc., and the answer is the former. Even if the “fecal-contaminated soil” part sounds weird, it might be the only answer that involves ingestion, which you therefore know must be correct.
Ascaris lumbricoides
Giant roundworm. Infection is called Ascariasis.
Causes intestinal obstruction.
USMLE can give vignette of patient with eosinophilia with high-pitched or absent bowel sounds (both findings that can reflect obstruction), and the answer is just Ascariasis or Ascaris lumbricoides. Not dramatic.
Treat with mebendazole.
Enterobius vermicularis
Aka pinworm (asked on USMLE, where student got easy vignette + all of the worms listed were colloquialisms rather than actual binomial nomenclature).
Causes perianal itching.
Diagnosed via Scotch tape test, where eggs around the anal verge can be collected using tape.
Treat with mebendazole.
Toxocara canis
Carried by pet dogs. Acquired through ingestion of contaminated-soil/food.
Causes visceral larva migrans, which can cause hepatosplenomegaly.
Treat with mebendazole.
Trichinella spiralis
Acquired from pork and bear meat consumption.
Trichinosis presents as triad of 1) fever, 2) myalgias, and 3) periorbital edema in patient who ate bear meat or pork.
Treat with mebendazole.
Strongyloides stercoralis
Invades usually through the feet. Travels through the bloodstream to the lungs, causing pulmonary symptoms. The larvae ascend the trachea and are then swallowed into the GI tract, where they cause abdominal symptoms.
USMLE will give you school-age girl in rural Louisiana (I’ve seen this on NBME) who has pulmonary and abdominal symptoms + worms isolated from the GI tract + they ask for the mode of transmission –> answer = “through the feet.”
Treat with mebendazole.
Hookworms
Ancylostoma duodenale and Necator americanus are hookworms. USMLE loves these.
They enter through the feet + travel to the lungs, same as Strongyloides. The difference is that when they eventually enter the GI tract, they suck blood from their site of attachment in the small bowel, causing microcytic anemia due to iron deficiency.
The USMLE will not list Strongyloides alongside the hookworms as separate answers in the setting of pulmonary symptoms. What they will do is give you patient with eosinophilia + microcytic anemia, where the answer is a hookworm. Or they will give helminth infection + pulmonary symptoms + microcytic anemia, and the answer is simply “through the feet,” or one of the hookworms as the Dx.
Treat with mebendazole.
Onchocerca volvulus
Causes onchocerciasis (river blindness). Transmitted by black fly and causes black skin lesions and blindness.
Everything is Black: Black fly, Black bite, Black eyesight (blindness).
Will be kid in South America or Africa who has a skin lesion + blindness, where Onchocerca volvulus is only helminth listed that causes blindness.
Treat with ivermectin.
Wuchereria bancrofti
Causes elephantiasis (aka lymphatic filariasis), which is massive swelling due to lymphatic insufficiency.
Transmitted by female mosquito.
Treat with mebendazole.
Loa Loa
Roundworm that presents crawling in the eyeball.
Transmitted by deer, horse, or mango fly.
Treat with mebendazole.
USMLE wants you to know that tapeworms have a segmented body and a scolex, which refers to the head of the tapeworm that has “suckers and hooks.” USMLE is known to show this image on the real exam + expect you to know you’re looking at a tapeworm because of the characteristic scolex.
Diphyllobothrium latum
Aka fish tapeworm. Acquired from ingesting – you’d never guess it – fish.
Causes B12 deficiency, leading to macrocytic anemia and hypersegmented neutrophils.
This is in contrast to hookworms (N. americanus and A. duodenale; nematodes), which cause microcytic anemia.
Treat with praziquantel.
Taenia solium
Aka pork tapeworm. Acquired from pork consumption, usually in someone who went abroad to, e.g., Mexico.
Causes cysticercosis, which presents as muscle pain/cysts, and neurocysticersos, which presents as lesions within the brain. The latter can present one of three ways on NBME (as per my observation): 1) swiss-cheese appearance of brain (buzzy); 2) one or two ring-enhancing lesions; 3) cystic, soap-bubble-appearing lesions within the ventricles.
I’ve specified in the past that praziquantel is preferred for cysticercosis and albendazole for neurocysticercosis (rare use of a -bendazole for a non-nematode), but USMLE actually doesn’t give a fuck, and they won’t list both side by side anyway. You should just know that praziquantel is basically always the answer for cestodes and trematodes, but that albendazole (normally a nematode agent) can be used for neurocysticercosis. But if you’re ever asked this on the real exam, they will give you obvious Taenia solium infection, where the answer is the only anti-helminth drug listed, so there won’t be any confusion.
Don’t confuse Taenia solium (pork cestode) with Trichinella spiralis (pork/bear nematode, which is triad of 1- periorbital edema, 2- myalgias, 3- fever, in someone who ate pork or bear).
Echinococcus granulosus
Causes hydatid cyst disease.
Presents with liver cysts, and sometimes jaundice and general flu-like symptoms.
Do not biopsy the cysts. This can cause anaphylaxis. The correct management is surgical excision of the cysts + praziquantel.
Schistosoma hematobium
Snails are the reservoir. But the trematode isn’t acquired via consumption. It is acquired through the skin in someone swimming in (usually) Africa. Travels to the cystic veins draining the bladder + the bladder wall.
Causes hematuria and squamous cell carcinoma of the bladder.
USMLE vignette will say some guy was swimming in Africa + now has hematuria and eosinophilia. The Q need not ask about SCC of the bladder.
This is in contrast to smoking, industrial (aniline) dyes, and naphthylamine (moth balls), which cause transitional cell carcinoma of the bladder and urothelial tract.
Treat with praziquantel.
Schistosoma mansoni/japonicum
Same as S. hematobium, snails are the reservoir, but the trematode isn’t acquired via consumption. It is acquired through the skin in someone swimming in (usually) Africa. Travels to the mesenteric veins / intestines, before making its way to the liver.
Can cause hepatosplenomegaly, liver damage, and GI symptoms.
There is Q on NBME exam where they show picture of a worm + say there’s hepatosplenomegaly, and then Schistosoma mansoni is the answer, but it’s not a hard Q because it’s the only reasonable organism listed.
Treat with praziquantel.
Clonorchis sinensis.
Acquired via consumption of contaminated fish.
Can cause cholangiocarcinoma (bile duct cancer).
Treat with praziquantel.
Paragonimus westermani
Acquired via consumption of crab meat or crayfish.
Travels from the GI tract to the lungs, where it causes hemoptysis.
Treat with praziquantel.
