Nematode Zoonoses - TRICHINOSIS

AGENT:

Trichinella spiralis, an intestinal nematode.

RESERVOIR AND INCIDENCE

Swine, dogs, cats, rats and many wild animals. Worldwide. In the U.S., there has been a marked reduction in the prevalence of trichinosis both in humans and pigs; prevalence in commercial pork now ranges from nil to 0.7%. Fewer than 100 human cases are reported annually and usually have been as a result of eating homemade sausage and other meat products using pork, horse meat, or arctic mammals.

TRANSMISSION:

In the natural cycle, larvae develop into adult worms in the intestines when a carnivore ingests parasitized muscle. Pigs generally become infected by feeding on uncooked scraps or, less often, by eating infected rats. In humans, infection occurs by eating insufficiently cooked meat. In the epithelium of the small intestine, larvae develop into adults. Gravid female worms then produce larvae, which penetrate the lymphatics or venules and are disseminated via the bloodstream throughout the body. The larvae become encapsulated in skeletal muscle.

DISEASE IN ANIMALS:

Usually subclinical.

DISEASE IN HUMANS:

Clinical disease in humans is highly variable and can range from inapparent infection to a fulminating, fatal disease depending on the number of larvae ingested. Sudden appearance of muscle soreness and pain, together with edema of upper eyelids are common early and characteristic signs. These are sometimes followed by subconjunctival, subungual and retinal hemorrhages, pain and photophobia. Thirst, profuse sweating, chills, weakness, prostration and rapidly increasing eosinophilia may follow. GI symptoms may also occur. Remittent fever, cardiac and neurologic complications may appear. Lastly, death due to myocardial failure may occur.

DIAGNOSIS:

Serologic testing and muscle biopsy.

TREATMENT:

Treatment is principally supportive, since in most cases recovery is spontaneous. Mebendazole, thiabendazole, or albendazole can be given.

PREVENTION/CONTROL:

Cooking (at 77ºC [171ºF] or above) destroys the parasite. Freezing meat up to 15 cm at 5ºF for 30 days or -13ºF for 10 days will destroy the parasite. Thicker pieces need to be frozen at the lower temperature for at least 20 days. These temperatures will not kill the cold-resistant Arctic strains, however. Gamma irradiation will kill the parasite. Prevent pigs from gaining access to rats or uncooked offal.