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Nematodes in the genus, Trichostrongylus. Although primarily parasites of animals, several species of Trichostrongylus have been known to infect humans, including T. orientalis, T. colubriformis, and T. axei.
Eggs are passed in the stool of the definitive host (usually a herbivorous mammal) , and under favorable conditions (moisture, warmth, shade), larvae hatch within several days. The released rhabditiform larvae grow in the soil or on vegetationl , and after 5 to 10 days (and two molts) they become filariform (third-stage) larvae that are infective . Infection of the human host occurs upon ingestion of these filariform larvae . The larvae reach the small intestine, where they reside and mature into adults. Adult worms inhabit the digestive tract of their definitive hosts and may occur as incidental infections in humans .
Worldwide, but more common where livestock is raised.
Most infections are asymptomatic. Heavy infections can cause gastrointestinal problems (abdominal pain, diarrhea, anorexia), headache, fatigue, anemia and eosinophilia.