Biomedical Engineering Reference
In-Depth Information
In addition to Strongyloides stercoralis, other species that have been
reported to infect humans are: Strongyloides fuelleborni and Strongyloides
kellyi.
Class Anyclostomadea contains the two species responsible for nearly all
cases of hookworm disease in humans: Ancylostoma duodenale and Necator
americanus. The two species have similar clinical presentations, but different
geographic distributions. Ancylostoma duodenale is common in the Middle
East, North Africa, and India. Necator americanus is common in North and
South America, as well as parts of Africa and Asia. Hookworms infect about
600 million people.
Hookworm eggs and larvae live in soil. Like the previously described
member of Class Rhabditida, Strongyloides stercoralis,larvaeofAncylostoma
duodenale and Necator americanus penetrate the skin of human hosts.
Ancylostoma duodenale may also infect by oral ingestion. The larvae invade
tissues and travel to the lungs, where they travel up the bronchial tree, eventu-
ally dropping into the esophagus, passing down the alimentary tract to the
small intestine, where they mature into adults. Eggs laid by the female adult
worms pass into the environment, with feces. Humans are the only natural
host for the hookworms. There is no secondary host.
The distinctive biological feature of the hookworms, distinguishing them
from other nematodes, is hemophagia (i.e., blood eating). The hookworms
suck blood from the host, producing anemia and malnutrition. Children are
particularly vulnerable to the effects of hookworm infection, which may
cause delays in mental and physical development.
Ancylostoma brasiliense is a hookworm of dogs and cats. It occasionally
penetrates the skin of humans, a dead-end host, and causes localized inflam-
mation of the skin or limited subcutaneous migration (cutaneous larva
migrans or creeping eruption).
Class Metastrongylidae contains two genera that contain infectious organ-
isms: Angiostrongylus and Trichostrongylus.
Angiostrongylus cantonensis is a parasitic nematode (roundworm) that
causes angiostrongyliasis, the most common cause of eosinophilic meningitis
in Southeast Asia. Angiostrongylus cantonensis lives in the pulmonary arter-
ies of rats; hence its common name, rat lungworm. Snails are the most com-
mon intermediate hosts, where larvae develop until they are infective.
Humans are incidental hosts of this roundworm, and may become infected
through ingestion of raw or undercooked snails or from water or
vegetables contaminated by snails or slugs or deposited larvae. Ingested lar-
vae travel through the blood to the brain, where the larvae may die or may
progress to juvenile adults before eventually dying. The dead and dying
organisms produce an allergic inflammatory reaction in the brain, with an
increase in eosinophils in cerebral spinal fluid. Other species of Genus
Angiostrongylus that may infect humans include Angiostrongylus costaricen-
sis and Angiostrongylus mackerrasae.
