THE MERCK VETERINARY MANUAL
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Trichuris sp in Pigs

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Trichuris suis is found worldwide in pigs. The adult worms are 5–6 cm long and whip-shaped; the anterior slender portion embeds within the epithelial cells of the large intestine, especially the cecum, with the thickened posterior third lying free in the lumen. Infection is by ingestion of embryonated ova. Heavy infections may cause inflammatory lesions in the cecum and adjacent large intestine and may be accompanied by diarrhea and unthriftiness. Infection is most often seen in young animals; resistance is both acquired and age-related. The double-operculated brown eggs (50–68 × 21–31 mm) are diagnostic, with egg excretion commencing 6–7 wk after infection. However, trichurids have a short period of egg-laying (2–5 wk) before the worms are expelled by immune-mediated reactions, and thus little significance can be given to percentage of egg-excreters and numbers of eggs per gram of feces. Dichlorvos, levamisole, some benzimidazoles, and ivermectin are effective against the adult worms. Biologically, the eggs are comparable to Ascaris eggs—they are highly resistant to chemicals and may remain infective for up to 11 yr; control relies on thorough cleaning of the affected area and moving the animals to clean plots. Trichuris eggs develop rather slowly (10–12 wk under optimal conditions), and because they do not develop at temperatures <16°C, there is only 1 generation/yr in temperate regions.

T suis larvae may hatch in the large intestine of humans, in which the larvae seem to be able to establish transiently. Adults are rarely seen.

Last full review/revision March 2012 by Allan Roepstorff, DSc, PhD, MSc

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