Immunity to experimental neosporosis in pregnant sheep

Neospora caninum is an important cause of fetal loss in cattle but has also infrequently been shown to cause disease in sheep and goats. Experimental infection of pregnant sheep with N. caninum causes clinical and pathologica l changes very similar to those of neosporosis in cattle. An experiment in sheep was undertaken to examine whether infection with N. caninum before pr egnancy conferred immunity to subsequent challenge with the parasite during pregnancy. Primary inoculation of NCl tachyzoites subcutaneously, either b efore or during pregnancy, caused a significant temperature response in ewe s, while those given a secondary challenge at 90 days gestation (dg) did no t show such a response. Primary infection of 12 ewes during pregnancy resul ted in the loss of all fetuses while a further 12 ewes inoculated with NCl tachyzoites before mating and subsequently challenged with the same dose at 90 dg produced nine live and seven dead lambs. There were no fetal deaths in ewes only infected with Neospora before mating although there was serolo gical evidence of vertical transmission in four of their clinically normal offspring while Neospora DNA was detected in the cerebrospinal fluid of a f ifth healthy lamb. Thus an experimental primary infection with N. caninum d uring pregnancy killed all the fetuses while inoculation before pregnancy d id not cause any mortality but did provide a degree of protection against s ubsequent challenge with Neospora during pregnancy.