Primary and secondary infections of the domestic chicken with Trichostrongylus tenuis (Nematoda), a parasite of red grouse, with observations on the effect on the caecal mucosa

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Abstract
SUMMARY: The course of primary and secondary infections with Trichostrongylus tenuis in the domestic chicken was investigated. Primary infections were established after the administration of single and trickle doses of infective-stage larvae. The worm burden in the caeca was highest after a single dose of 500 infective-stage larvae; this gave a mean of 87 nematodes per bird on days 8–9 of infection, 20 nematodes on day 14 and 0 on day 28 of infection. Following trickle doses of 60, 100, 200, 300, 400 or 500 infective-stage larvae, there was a rise and then a fall in nematode egg output in all groups. In chickens given a primary dose of 500 infective-stage larvae followed 30 days later by a single secondary dose of 500 infective-stage larvae, the mean worm burden during the secondary infection rose to 57 nematodes on day 9 of infection and then fell rapidly to 18 nematodes on day 15 and to 2 on day 30. Scanning electron microscopy showed changes in the caeca of infected birds, with the caecal surface being covered in a layer of mucus from 12 days after infection. Balls of blood-stained mucus containing nematodes were observed in the caecal droppings from day 9 of infection onwards. It is concluded that chickens rapidly expel an established infection of T. tenuis, unlike the normal host, the red grouse.