Biomedical Engineering Reference
In-Depth Information
Nematoda
Secernentea
Ascaridida
Anisakidae
*Anisakis
*Contracaecum
*Pseudoterranova
Anisakiasis is the disease produced by members of Class Anisakidae,
which includes the following genera: Anisakis, Contracaecum, and
Pseudoterranova. Humans are infected by eating undercooked shellfish
infected with larvae. Most cases occur in countries where raw fish is regu-
larly consumed. Only a handful of cases are reported in the USA annually.
Humans are a dead-end host for the worms. After ingestion, the larvae travel
to the small intestine, and live for a time, eventually dying without reprodu-
cing. In rare cases, they may cause abdominal obstruction, but their most
clinically significant effect is through an acute allergic reaction. An acute
enteritis often occurs, or, in some cases, a generalized anaphylactic reaction.
Some fishermen are so highly sensitized that they develop hyper-immune
reactions simply from handling fish or crustaceans that are infected with the
larvae.
Nematoda
Secernentea
Ascaridida
Ascarididae
*Ascaris
*Baylisascaris
Ascaris lumbricoides, the cause of ascariasis, infects about 1.5 billion people
worldwide, making it the most common helminth (worm) infection of
humans [90]. Most cases occur in tropical regions, particularly in Africa and
Asia. Humans are the exclusive primary host, for the organism.
Infection occurs when humans ingest embryonated eggs contaminating
water or food.
The ingested embryonated eggs produce larvae in the small intestine. The
larvae invade through the intestinal wall and into the portal system, where
they are transported to the alveoli of lungs. From there, they invade into the
bronchial system, move upwards to the pharynx, and drop back into the
intestinal system via the esophagus. The worms reach adulthood in the intes-
tine, where they can grow to nearly 40 cm in length and have a lifespan of
up to two years. While in the lungs, they can produce a pneumonitis. Ascaris
lumbricoides is not the only helminth that migrates through the lungs.
In Class Rhabditida, Ancylostoma duodenale, Necator americanus, and
Strongyloides storcoralis invade the pulmonary system.
