Parasitology: Practice Question

A 43 year old male presents with complaints of muscle aches, diarrhea and abdominal pain. CBC shows absolute eosinophilia, and a muscle biopsy shows the presence of larvae. Which of the following is the most likely diagnosis?
  1. Trichinella spiralis
  2. Echinococcus granulosus
  3. Taenia solium
  4. Diphyllobothrium latum
  5. Hymenolepis nana
Show Answer and Explanations

Trichinella spiralis — Correct answer

Correct. Trichinella spiralis is a tissue nematode (round worm), the other being Dracunculus medinensis. It is commonly found in pigs, and is contracted from undercooked pork. It can cause muscle aches, diarrhea and abdominal pain. Tissues show encysted larvae with 2.5 spirals. Peripheral eosinophilia is common.

Echinococcus granulosus

Incorrect. Echinococcus granulosus is a tissue tapeworm and is common in sheep as an intermediate host. Carnivorous animals eat the sheep and become the definitive host. Humans are not a definitive host, and adults tapeworms are not found in humans. Instead, the parasite forms hydatid cyst disease; cysts are common in the liver but can form anywhere in the body. The rupture of a cyst, from trauma or biopsy, can cause anaphylactic shock. As such, it is more commonly diagnosed by ELISA, serology or other molecular techniques.

Taenia solium

Incorrect. Taenia solium (pork tapeworm) causes intestinal infection with generally mild abdominal pain and diarrhea. However, if humans ingest ova, the larval form can spread through the body to cause cysticercosis, which can be fatal. The scolex (the worm's head) has two crowns of hooks on the rostellum (a protrusion from the head). The proglottid (body segments - contain eggs) has less than 13 striations / lateral uterine branches per side. Eggs have a thick shell with radial striations and a six hooked oncosphere inside.

Diphyllobothrium latum

Incorrect. Diphyllobothrium latum is the fish tapeworm, and is acquired from undercooked fish. Unlike other tapeworms, the proglottids (body segments) are more wide than long). Eggs are 70-80 um and smooth, a terminal knob can be appreciated opposite the operculum (the knob is also seen in Clonorchis sinensis, but C. sinensis eggs are smaller and have a more prominent "shouldered" operculum). It can cause B12 deficiency.

Hymenolepis nana

Incorrect. Hymenolepis nana ("dwarf tapeworm") is the most common tapeworm infection in the U.S. (the most common worm infection in the U.S. is Enterobius vermicularis). It is spread from the feces of mice or other humans. Disease is asymptomatic to causing mild diarrhea. Eggs are 40 to 60 um and have two poles. The eggs have two layers, and 3 pairs of hook-like filaments spread out between the two layers. The oncosphere (larval stage) has six hooks inside the egg.

Summary

Summary: Trichinella spiralis is is a tissue nematode (round worm), the other being Dracunculus medinensis. It is commonly found in pigs, and is contracted from undercooked pork. It can cause muscle aches, diarrhea and abdominal pain. Tissues show encysted larvae with 2.5 spirals. Peripheral eosinophilia is common.
Build a Free Exam