Production of Sarcocystis gigantea sporocysts by experimentally infected cats

A study of 28 infections in 22 individually housed cats fed excised cysts of Sarcocystis gigantea from naturally infected sheep, revealed a consistent pattern of sporocyst shedding. In all cats, sporocyst excretion commenced 10 or 11 days postinfection (PI). Peak production occurred between 13 and 22 days PI, in most instances on Days 17and 18. Peaknumbers (rounded) rangedfrom 550 to 260 000 (mean = 53 000) sporocysts per gram of faeces or from 38 000 to 6.6 million (mean = 1.7 million) sporocysts per day. The number of days sporocysts were shed ranged from 26 to at least 60 days PI but in 26 of the 28 infections examined, > 80% of the total sporocyst yield was produced within 30 days of infection. The total numbers of sporocysts produced by individual cats over the patent period ranged from 164 000 to 56.6 million (mean = 12.7 million). These numbers tended to increase with increasing infective dose and tobe greater in those cats receiving multiple rather than equivalent single doses. Neither the sex of the cat, nor experience of one or two previous infections, had any significant effect on the numbers of sporocysts shed.