Contact with soil contaminated with eggs or larvae of nematode
parasites is a common form of transmission that results in human infection. The
nematodes can live for years as adults in the human intestinal tract. Soil
becomes contaminated by fecal material of infected humans and other animal
More than a billion people are infected with at least one species.
The most important nematode infections of the human gastrointestinal tract are
the intestinal roundworm (Ascaris
lumbricoides), whipworm (Trichuris trichiura),
and hookworm (Necator
americanus or Ancylostoma duodenale).
It is common for a single individual, especially a child living in a less
developed country, to be chronically infected with all three of the nematode
parasites, which results in malnutrition, stunted growth stunting, retarded
intellectual development, and cognitive and educational deficiencies.
Rhabditiform larval stages feed on bacteria associated with organic matter.
Adult stage feeds on blood and tissue from the intestinal lining of the host.
Parasites draw mucus into their buccal cavity and suck the blood and tissue. The action of
digestive juices and the shearing of teeth form a bolus of tissue that is separated from the host gut and
Host blood is drawn almost continuously into the intestine and passed out through the anus.
Blood plasma and corpuscles undergo at least partial digestion in the nematode.
consume up to 1 ml blood per individual per day.
When it reaches the small intestine of the host, the the infective filariform larva molts a fourth and final time and develops to maturity in about five weeks.
Adult hookworms (Ancylostoma
duodenale and Necator americanus)
parasitize the upper part of the human small intestine, whereas
Ascaris lumbricoides parasitize the entire
small intestine and adult
Trichuris trichiura live in the large intestine, especially the caecum.
The parasites can live for several years in the human
gastrointestinal tract. After mating, each adult female produces thousands of
eggs per day which leave the body in the feces.
Infection by a hookworm usually results in bloody diarrhea and anemia.
Hookworm infections undermine the health of the host, causing stunting of growth and general laziness.
Often accompanied by acute mental distress.
Bethony, J., Brooker, S., Albonico, M., Geiger, S.M., Loukas, A., Diemert,
D., Hotez, P.J. 2006.
Soil-transmitted helminth infections: ascariasis, trichuriasis, and hookworm.
The Lancet 9521:1521-1532.
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