Endogenous transplacental trasnmission of Neospora caninum infection in naturally infected sheep

Abstract

Neospora caninum has traditionally been considered an unimportant parasite in sheep. However, recent studies carried out in Spain have shown that this protozoan can cause severe reproductive failure in sheep. The importance of ovine neosporosis should therefore be reconsidered and the mechan¡sms of transmission studied in depth. This study aimed to evaluate the efficacy of endogenous transplacental transmission of N. caninum in sheep. A total of 28 seroposit¡ve sheep were housed in facilities in which horizontal infection was precluded. The sheep were mated, giving r¡se to 24 pregnant sheep in which ultrasound scans (for pregnancy follow up) and blood sampl¡ng (for antibody detection) were carried out monthly. Three of the sheep aborted 5 foetuses and 21 of the sheep gave birth to 11 stillborn and 39 live lambs. Ten lambs were born weak and died within a week of birth. Precolostral serum samples were collected from all live newborn lambs for antibody detection. -Brain samples were obtained from all aborted, stillborn and dead lambs for parasite DNA detection and histological analysis. All sheep remained seropositive throughout pregnancy. Precolostral antibodies were also detected in 38 out of 39 newborn lambs. Parasite DNA was detected in all dead lambs (21) and in all foetuses except one (4/5). Scarce histological lesions consistent with protozoan infection (glial foci) were observed in 16 brains. ln 13 out of these 16 cases, N. caninum tissue cysts were detected by immunohistochemistry. The results show conclusively that endogenous transplacental transmission of neosporosis is highly efficient in sheep.