Response of unimmunized and sporozoite-immunized chickens to challenge with avian Eimeria species: effects of intraperitoneal injection of Sephadex.

Unimmunized chickens, given intraperitoneal injections of Sephadex at the same time that they were inoculated with oocysts of either Eimeria tenella or E. acervulina, had significantly lower lesion scores at 6 days postinoculation (PI) than unimmunized chickens that were injected with saline instead of Sephadex. Despite the difference in lesion scores, there was little effect on weight gain, except in one experiment, in which Sephadex-injected chickens gained significantly more weight than saline-injected chickens. In contrast, in chickens that were immunized by prolonged exposure to sporozoites of E. adenoeides, injection of Sephadex at the time of challenge with E. tenella did not reduce lesion scores or parasite development as compared with the uninjected chickens, and the weight gain of the Sephadex-injected challenged chickens fell to a level significantly lower than that of their saline-injected challenged counterparts. The data indicate that Sephadex injected at the time of oocyst inoculation 1) produces markedly different effects on lesion scores and weight gain in unimmunized and immunized chickens and 2) abrogates sporozoite-elicited immunity against E. tenella challenge.