Infectivity and sporogony ofCaryospora-type oocysts ofIsospora rivolta obtained by heating

Abstract

The infectivity and sporogony ofCaryospora-type oocysts ofIsospora rivolta obtained by heat treatment were examined. Fresh unsporulated oocysts ofI. rivolta were heated at 50°C for 5 min, then poured into a cold 2% potassium dichromate solution and incubated at 25°C. To observe the stage of sporulation, 100 oocysts were examined at 2-h intervals after incubation. The earliest sporulated oocysts were observed at 14 h and the sporulation time was 22 h, similar to that of nontreated oocysts. To determine the infectivity, onlyCaryospora-type oocysts were collected after sporulation and inoculated orally into cats and mice. The mice were killed at 7 days after inoculation, and their mesenteric lymph nodes and spleens were fed to other cats. All of these cats shed oocysts. The newly discharged oocysts developed into theIsospora type after sporulation. These results suggest that theCaryospora-type oocysts transformed only morphologically after heat treatment and were as infective as the nontreated oocysts to host antimals.