Trichinosis

A human host who eats T. spiralis infected meat may experience symptoms to a varying degree. If the meat ingested has only a few cysts, then the human host's "worm burden" is said to be relatively small, so that symptomatology will be relatively moderate. In fact, many infections are subclinical (exhibiting such mild symptoms as to remain undiagnosed).

In a host with a greater worm burden, the initial symptoms will be caused by the presence of the adult worms in the intestine, and usually include fever, diarrhea, abdominal pain, and perhaps vomiting. These symptoms begin about one to two days after eating the offending meat, and may last for a week or so.

When larvae begin their migration through the blood vessels, the host will begin to experience systemic symptoms (affecting the whole body), such as fever, swelling of the face and the area around the eyes, rash, bleeding into the nail beds, retina, and whites of the eyes, and cough. In very severe cases, inflammation of the heart muscle (myocarditis), lungs (pneumonitis), or brain (encephalitis) may occur, which can lead to the few deaths attributable to trichinosis.

The larvae begin to burrow into the host's muscles and form cysts within about two to three weeks of the initial infection. This produces signs of muscle inflammation (myositis), including swelling of the affected muscle groups, pain, and weakness.

The most frequently affected muscles are the muscles outside of the eye, which control eye movements (extraocular muscles), as well as the muscles of the jaw, neck, upper arm (biceps muscle), lower back (lumbar region), and diaphragm (the muscle which separates the abdominal and chest cavities and aids in inspiration).

Symptoms are at their most severe at about three weeks after infection and decrease very slowly in their severity. Recovery is extremely gradual, and symptoms may be present for as long as three months. Fatigue and myalgia (muscle pain) may take several more months to subside.