Trichuris sp in Pigs
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 eggs containing an infective first-stage larva. The larva hatches and penetrates the distal ileum, cecal, and colonic mucosa. The nematodes complete all four molts, after which the posterior end begins to protrude into the lumen. The prepatent period is 6–8 wk; longevity is 4–5 mo. Light infections, with no clinical signs, are generally the case. Heavy infections may cause inflammatory lesions in the cecum and adjacent large intestine and may be accompanied by diarrhea and unthriftiness. Clinical 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. Eggs are heavy; thus, good technique with media of proper specific gravity is essential. 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. Clinical trichurosis is usually associated with the larval stages before eggs are passed in the feces; in these cases, examining mucosal scrapings taken at necropsy for smaller stages of the parasite is recommended. Mature parasites are easily found after ingesta is washed away and can be identified by their size and whip-like form. Dichlorvos, levamisole, some benzimidazoles, ivermectin, and doramectin 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 3–4 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 one generation per year in temperate regions.
T suis larvae may hatch in the large intestine of people, in which the larvae seem to be able to establish transiently. It is this feature that has led to intense research interest in the treatment of inflammatory bowel disease, including ulcerative colitis and Crohn's disease, of people through administration of infective T suis eggs.