Worm-like helminth parasites are generally classified into two phyla, which are further subdivided into the flatworms (Platyhelminthes) and the roundworms (Nematoda). The digital image presented below was captured with the MIC-D operating in brightfield illumination, and illustrates a stained thin section of human muscle infected with encysted larvae of the Trichinella spiralis roundworm.

Humans are usually infected with the parasite by eating undercooked pork containing the Trichinella larvae, which mature in a few days to a week. Male and female parasite worms mate in the host's intestine, and the female then burrows into the intestinal wall, where she deposits fully developed viable larvae (instead of ova) in the lymph nodes. Larvae traverse the lymphatic system and enter the blood stream, where they are distributed throughout the host and eventually encyst in striated muscle tissue. The most frequently infested muscles are the diaphragm, tongue, biceps, deltoids, and the abdominal walls.

Adult worms, which are 2 to 4 millimeters in length, are barely visible in fecal matter, but can be readily observed with a microscope in the stools of patients during the first few weeks of the infestation. At later stages, identification of Trichinella infestation is made through muscle biopsies and serological testing. The clinical symptoms of Trichinella infestation are mild gastrointestinal disturbances, painful respiration, and muscle pain. Heart muscle damage can ultimately occur.