The Influence of Age of Host on Infection with Eimeria tenella

Abstract

Excystation of E. tenella sporozoites was more rapid in chicks aged 4, 5, and 6 weeks than in those of 0, 1, 2, and 3 weeks. A greater proportion of unexcysted sporulated oocysts was found in the feces of birds aged 0 and 1 week than in any of the other age-groups studied, indicating less successful excystation in these birds. Oocyst production to a dose of 500 oocysts increased with age of host. Older birds tended to be more resistant to second and third infections than the younger birds but direct comparisons are difficult to make. Chickens of different ages are known to differ in their susceptibility to infection with Eimeria spp. (Tyzzer, Theiler, and Jones, 1932; Brackett and Bliznick, 1952; Gardiner, 1955; Long, 1959; Krassner, 1963; Doran and Farr, 1965). Various reasons for the age differences in susceptibility, such as length of intestine, availability of cells, and physiological conditions for sporozoite penetration have been advanced by the authors quoted above. Some earlier work in this laboratory which involved the excystation of E. tenella in very young chicks indicated that the percentage excystation increased with age of host. Consequently, we have examined the excystation of E. tenella in chicks of different ages and also the extent of the subsequent infection as shown by oocyst