What causes trichinosis?
Trichinosis is caused by Trichinella species (parasitic nematodes, intestinal worms, and roundworms) that initially enter the body when meat containing the Trichinella cysts (roundworm larvae) is eaten. For humans, undercooked or raw pork and pork products, such as pork sausage, has been the meat most commonly responsible for transmitting the Trichinella parasites. It is a food-borne infection and not contagious from one human to another unless infected human muscle is eaten. However, almost any carnivore (meat eater) or omnivore (eats meat and plants for food) can both become infected and, if eaten, can transmit the disease to other carnivores and omnivores. For example, undercooked or raw bear meat can contain livable Trichinella cysts. Therefore, if humans, dogs, pigs, rats, or mice eat the meat, they can become infected. In rare instances, larvae that inadvertently reaches cattle feed can infect cattle. There are six species that are known to infect humans:
- T. spiralis found in many carnivorous and omnivorous animals worldwide.
- T. britovi found in carnivorous animals in Europe and Asia.
- T. pseudospiralis found in mammals and birds worldwide.
- T. nativa found in arctic mammals (for example, bears, foxes).
- T. nelsoni found in African mammals (for example, lions, hyenas).
- T. murrelli found in wild animals in the U.S.
Two other species, T. papuae (found in pigs in New Guinea) and T. zimbabwensis (found in crocodiles in Tanzania) have not been reported to infect humans to date. There are other strains (antigenic variants related to named species) that are unnamed and can infect humans.