Trichinella spiralis

Background

Also known as the pork worm, not to be confused with pork tapeworm (Taenia solium)

Can complete its life cycle in a human, pig, boar, bear, walrus, fox, and other animals
Life cycle involves ingestion of meat with cysts, which develop into adult worms, which release eggs, which invade through gut mucosa and migrate to muscle, where it becomes a muscle cyst

Acquired in humans by ingestion of undercooked meat
Present in carnivores and omnivores worldwide
Commercial pork is the most common source of infection in humans, but can also be acquired from a number or wild game meats

Spectrum of illness from asymptomatic (most common) to fulminant infection
Incubation period less than 1 month
After ingestion of contaminated meat:
- Within first week, may experience abdominal discomfort, nausea, vomiting, and diarrhea
- After another 2 to 8 weeks, may have fever, myalgia, periorbital edema, urticarial rash, conjunctival hemorrhage, and subungual hemorrhage, related to migration of larvae into tissues
- In severe disease, after 1 to 2 months, can develop myocarditis, neurological symptoms, and pneumonitis
- Can cause an eosinophilic myositis
Often has eosinophilia during migratory phase (70%)
Larvae are viable in tissues to years, with calcification usually occurring between 6 and 24 months

Usually made clinically based on exposure history, eosinophilia, and symptoms
Serology exists, and can be used as paired acute and convalescent titres
- Positive after 2 to 3 weeks, and can stay positive for years
- Cross-reacts with other nematodes (and sometimes with other helminths)