ORAL INOCULATION OF CATS WITH TISSUE CYSTS OF NEOSPORA-CANINUM

Objective-To test the hypothesis that cats are definitive hosts of Neo spora caninum. Animals-6 weaned male kittens obtained from 2 sources, and several dozen outbred mice. Procedure-Cats were fed large numbers of 3 strains of N caninum: tissue cysts in buffered saline solution, m ouse brain homogenates, and whole carcass homogenates from seropositiv e mice. Fecal specimens were examined for 4 weeks by use of flotation tests; and bioassays were performed in mice. One cat was inoculated pa renterally with tachyzoites, to determine whether cats could respond s erologically to N caninum. Tissue cysts from portions of oral inocula were cultured to verify viability. Indirect fluorescent antibody serol ogic testing, histologic and immunohistologic examinations, cell cultu re; and polymerase chain reaction procedures were performed. 4 to 8 we eks after oral exposure, to seek evidence of infection of cats and mic e. Results-None of the cats or mice seroconverted to N caninum, with t he exception of the single cat inoculated parenterally. Fecal shedding df oocysts was not observed, except for Isospora felis oocysts that w ere shed by 2 cats beginning prior to oral challenge exposure. Evidenc e of infection was not detected, in tissues of cats' or mice, with the exception of the parenterally inoculated cat. Conclusions-The hypothe sis that cats are definitive hosts of N caninum is not supported. Clin ical Relevance-Extermination of cats in efforts to control bovine neos porosis is not warranted.