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Brief Summary

Trichostrongylus nematodes are intestinal (mainly) parasites of animals, primarily ruminant mammals, including domesticated mammals such as sheep, goats, and camels (but, e,g, T. tenuis parasitizes birds and T. retortaeformis infects rabbits; Hoste et al. 1998). Trichostrongylus vitrinus is a parasite of sheep and a major cause of ovine gastroenteritis worldwide (Temperley et al. 2009 and references therein). Several species of Trichostrongylus have been known to infect humans, including T. orientalis, T. colubriformis, T. vitrinus, and T. axei. A variety of Trichostrongylus species are found worldwide, but they are more common where livestock is raised. (Centers for Disease Control Parasites and Health website)

Trichostrongylus eggs are passed in the stool of the definitive host (usually an herbivorous mammal) and under favorable conditions (moisture, warmth, shade) larvae hatch within several days. The released rhabditiform larvae grow in the soil or on vegetation 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. (Centers for Disease Control Parasites and Health website) Adult worms inhabit the digestive tract of the definitive host and may occur as incidental infections in humans (e.g., Lattès er al. 2011, which describes several individuals in a family being infected by eating strawberries from a garden that had been fertilized with fresh, rather than dried, sheep manure from infected sheep).

Because Trichostrongylus infection of humans is uncommon (and often aymptomatic) and the worms may be difficult to identify, reported cases are rare. Eggs can be distinguished from those of Necator and Ancylostoma hookworms by the fact that they are longer and narrower. After 6 days of culture, T. colubriformis nematodes can be distinguished from similar stages in Strongyloides and Ancylostoma species by the bead-like swelling at the tip of the tail. In the absence of adult worms, which are rarely found in feces, sequencing of the ITS2 region is the most accurate method for specific identification of Trichostrongylus worms isolated from humans. (Lattès er al. 2011)

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