Trichinella spiralis

Background

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

Life Cycle

• 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

Epidemiology

• 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

Clinical Manifestations

• 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

Diagnosis

• 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)

Management

• Treated by albendazole or mebendazole