Excystation of the Sporozoites of Eimeria tenella in Apparently Unbroken Oocysts in the Chicken

SYNOPSIS. Chickens experimentally fed sporulated oocysts of Eimeria tenella were necropsied 5–300 minutes later to study excystation, especially in apparently unbroken oocysts. In birds killed 75–125 minutes after inoculation, there was evidence of excystation in some oocysts recovered from the small and large intestines. Altho not visibly broken, the shells of about 10% of the ones studied were wrinkled or otherwise deformed; many contained active sporozoites, some inside and some outside the sporocysts. During examinations, numerous sporozoites emerged from the sporocysts. Altho evidence was not obtained that excystation from unbroken oocysts was occurring inside the birds, the fact that it occurred in some oocysts during examinations may indicate that it could be taking place. Evidence of excystation was not seen in oocysts with shells that were not visibly altered.