Biomedical Engineering Reference
In-Depth Information
Eggs produced by the adult worms leave the intestine via the feces and
contaminate soil and water where sanitation is deficient. Adult worms may
produce a wide range of symptoms due to obstruction of the intestines and
of the ducts that connect with the intestine. Like members of Class
Anisakidae, Ascaris lumbricoides may provoke an allergic reaction. An
allergy to Ascaris lumbricoides may also precipitate allergic reactions to
shrimp and dust mites, as these unrelated species share antigens in common
with Ascaris lumbricoides.
Readers should be careful not to confuse ascariasis with the similar-
sounding anisakiasis (see above).
Baylisascaris procyonis causes baylisascariasis in humans. Raccoons are
the primary host. The adult nematode lives in the raccoon intestine and eggs
are dropped with raccoon feces. The eggs of Baylisascaris procyonis can sur-
vive for years, and they are extremely resistant to disinfectants and heat. In
rare circumstances, humans may become infected, as the secondary host, by
ingesting eggs. Eggs develop into larvae in the human intestine, and the lar-
vae migrate out of the intestines and through various organs, where they
eventually encyst. Involvement of the central nervous system by encysted
larvae is an extremely serious condition.
Nematoda
Secernentea
Ascaridida
Toxocaridae
*Toxocara
Humans are dead-end, accidental hosts for Toxocara canis (the dog toxocara)
and Toxocara cati (the cat toxocara). Infected animals pass eggs in their
feces. Larval development occurs within the eggs, and if matured eggs are
ingested by humans, the larvae can hatch in the small intestine. The larvae
migrate through various tissues: eyes, lung, liver, and brain being common
destinations.
The disease caused by toxocara organisms is toxocariasis. During the
migratory stage, the disease is often referred to as visceral larva migrans.
Eye involvement is referred to as ocular larval migrans. Readers should not
be lulled into a false sense of terminologic security. When toxocara migrate
through the skin, the condition is NOT called cutaneous larva migrans: this
term is reserved for cutaneous manifestations of Ancylostoma brasiliense.An
immune response to the migrating toxocara larvae may produce eosinophilia
(i.e., an increase of eosinophils in the peripheral blood), and the term eosino-
philic pseudoleukemia has been used to describe this condition.
After a period of migration, the worms, which cannot mature further in
the human body, encyst, to produce small, localized, permanent nodules in
tissues.
