The role of Neospora caninum in three cases of unexplained ewe abortions in the southern North Island of New Zealand

Unexplained abortions observed in three southern North Island sheep farms were investigated to determine if there was an association with Neospora caninum infection. Ewe hoggets and ewes on three farms that exhibited a persistent abortion problem, despite vaccination against Toxoplasma and Campylobacter infections, were chosen for this study. Blood was obtained from aborting, non-aborting and selected ewes that had dead foetuses at scanning. Some ewes were euthanized and examination of their uterine contents, gross examination and histopathology were performed. Serology was conducted for N. caninum, Toxoplasma gondii and Leptospira interrogans serovar Pomona and Leptospira borgpetersenii serovar Hardjo antibodies. Whole blood and selected tissues were used in polymerase chain reactions (PCR) to detect DNA from N. caninum and T. gondii. Gross examination and histopathology was not diagnostic and no bacterial pathogens were isolated. N. caninum indirect fluorescent antibody test (IFAT) serology identified 19 of 67 samples as positive, with titres ranging from 1:100 to 1:800. Serological results for Toxoplasma and Leptospira were generally negative or had low (1:100 dilution) titres, indicative of vaccination or previous exposure. N. caninum DNA was also detected by PCR in 23 of 64 samples, including in aborted foetal material. T. gondii DNA was detected by PCR in only 2 of the 64 blood samples. The results of these current investigations are suggestive of an association between N. caninum infection and abortion in sheep within New Zealand.Clinical relevance: N. caninum may be an important cause of sheep abortions.