Immunity to experimental neosporosis in pregnant sheep

Abstract

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 pathological changes very similar to those of neosporosis in cattle. An experiment in sheep was undertaken to examine whether infection with N. caninum before pregnancy conferred immunity to subsequent challenge with the parasite during pregnancy. Primary inoculation of NC1 tachyzoites subcutaneously, either before or during pregnancy, caused a significant temperature response in ewes, while those given a secondary challenge at 90 days gestation (dg) did not show such a response. Primary infection of 12 ewes during pregnancy resulted in the loss of all fetuses while a further 12 ewes inoculated with NC1 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 serological evidence of vertical transmission in four of their clinically normal offspring while Neospora DNA was detected in the cerebrospinal fluid of a fifth healthy lamb. Thus an experimental primary infection with N. caninum during pregnancy killed all the fetuses while inoculation before pregnancy did not cause any mortality but did provide a degree of protection against subsequent challenge with Neospora during pregnancy.

Detection of Neospora caninum DNA in semen of experimental infected rams with no evidence of horizontal transmission in ewes

“…Repeat abortions in subsequent years have also been reported (Jolley et al, 1999). In addition, studies have shown that experimentally infected sheep will seroconvert and abort in a dose dependent manner (Buxton et al, 1998(Buxton et al, , 2001Weston et al, 2009). These reports suggest that N. caninum infections can and do occur and cause disease, although it has generally not been regarded as a significant cause of abortion in sheep Otter et al, 1997;Buxton et al, 1998;Helmick et al, 2002).…”

Transplacental transmission of Neospora caninum in naturally infected small ruminants from northeastern Brazil

“…Buxton et al (2001) stated that autolysis difficult the histopathological analysis of aborted fetuses' tissues.…”

Vertical transmission in experimentally infected sheep despite previous inoculation with Neospora caninum NcNZ1 isolate

“…(Howe et al, 2012(Howe et al, , 2008Hassig et al, 2003;Kobayashi et al, 2001). Experimental studies have shown that sheep will seroconvert, abort in a dose dependent manner and may have repeated abortions in subsequent pregnancies (Weston et al, 2009;Buxton et al, 2001;Jolley et al, 1999). Nevertheless, the role of N. caninum as a significant pathogen and abortifacient in sheep is still unclear and knowledge about its epidemiology, especially the mode of transmission of neosporosis in sheep, is limited (Helmick et al, 2002;Otter et al, 1997).…”