Causal Agents:

Trichinellosis (trichinosis) is caused by nematodes (roundworms) of the genus Trichinella. In addition to the classical agent T. spiralis (found worldwide in many carnivorous and omnivorous animals), several other species of Trichinella are now recognized, including T. pseudospiralis (mammals and birds worldwide), T. nativa (Arctic bears), T. nelsoni (African predators and scavengers), and T. britovi (carnivores of Europe and western Asia).

Life Cycle:

Trichinella life cycle

Trichinellosis is acquired by ingesting meat containing cysts (encysted larvae) The number 1 of Trichinella. After exposure to gastric acid and pepsin, the larvae are released The number 2 from the cysts and invade the small bowel mucosa where they develop into adult worms The number 3 (female 2.2 mm in length, males 1.2 mm; life span in the small bowel: 4 weeks). After 1 week, the females release larvae The number 4 that migrate to the striated muscles where they encyst The number 5. Trichinella pseudospiralis, however, does not encyst. Encystment is completed in 4 to 5 weeks and the encysted larvae may remain viable for several years. Ingestion of the encysted larvae perpetuates the cycle. Rats and rodents are primarily responsible for maintaining the endemicity of this infection. Carnivorous/omnivorous animals, such as pigs or bears, feed on infected rodents or meat from other animals. Different animal hosts are implicated in the life cycle of the different species of Trichinella. Humans are accidentally infected when eating improperly processed meat of these carnivorous animals (or eating food contaminated with such meat).

Life cycle image and information courtesy of DPDx.

Page last reviewed: August 8, 2012