Biomedical Engineering Reference
In-Depth Information
Genus Trichostrongylus contains a variety of species that infect a wide
range of animals; ten species are known to infect humans. Humans are
infected when larvae are ingested in contaminated water or vegetables. The
larvae mature in the gut, and adult organisms live in the small intestine.
Infections are often asymptomatic. Symptoms, when they occur, are typically
those of enteritis. Eosinophilia (increased eosinophils in the blood) often
occurs, and severe symptoms arise in some individuals.
Nematoda
Enoplea
Dorylaimida
Trichocephalida
Trichinellidae
*Trichinella
*Capillaria
Trichuridae
*Trichuris
The nematodes that cause infection in humans belong to the Class
Secernentea or Class Enoplea. The human pathogens in Class Secernentea
have been described (see above). Class Enoplea has three genera containing
species that are infections in humans: Trichinella, Capillaria, and Trichuris.
Trinchinella spiralis is the cause of trichinosis, also known as trichinello-
sis. Humans are simultaneously the primary and the secondary host for this
organism, as the adult worms live in the intestines, producing eggs that hatch
into larvae within the body of the female adult. The female adult worms live
for about six weeks. The larvae leave the adult, penetrate the intestine and
migrate to muscles, where they wait to be eaten by another potential host.
Larvae live within individual muscle cells. This means that the parasitic
larva is much smaller than a single human cell. A full-length larva is about
80 microns in length. The larva curls tightly within the muscle cell, allowing
it to fit in a tight space.
Humans typically become infected when they eat undercooked meat.
More than 150 different animals have been reported as sylvatic hosts. Most
infections in the USA come from eating undercooked pork. In the early dec-
ades of the twentieth century, hogs were fed on pig meat, thus magnifying
the infectious burden in the hog population. Methods for cooking pork were
lax, and trichinosis in humans was common. With improved, regulated diets
for hogs, and with proper methods of cooking pork, the incidence of trichino-
sis in the United States has dropped. Clinically, trichinosis produces enteric
symptoms when the adult worms are reproducing in the intestines; muscle
aches when the larvae are invading muscle cells.
Hepatic capillariasis, caused by Capillaria hepatica, is a rare human
infection, with only a few dozen cases reported, most occurring in children.
Eggs in soil are ingested, hatched larvae penetrate the intestinal mucosa, the
