Immunity to sarcocystosis: modification of intestinal coccidiosis, and disappearance of sarcocysts in dairy goats.

Fifty, 2-3 month old dairy goats were each vaccinated orally with 10000 sporocysts of Sarcocystis capracanis and 25 age-matched goats served as uninoculated controls. Groups of vaccinated and control goats were challenged with lethal doses of S. capracanis at 95, 113, 205, and 274 days post-vaccination. Vaccinated goats developed subclinical sarcocystosis. Twenty-three vaccinated goats and 1 control goat died of intestinal coccidiosis and bacterial pneumonia, 15-118 days after vaccination. Myositis and degenerating sarcocysts were seen in muscles of goats necropsied at 90-186 days postvaccination. Very few, or no sarcocysts were seen in goats necropsied at 272 and 332 days post-vaccination. Vaccinated goats survived a lethal challenge inoculation indicating persistent protective immunity.