Molecular and Bioassay Examination of <i>Neospora Caninum</i> Infection in Bovine Aborted Fetuses in Khorasan Razavi Province, Iran.

<i>Neospora caninum</i> plays a significant role in causing abortion and reproductive failure in dairy cattle. The majority of neosporosis-related abortions occur during the 5-6 months of gestation. Outcomes can include fetal death within the uterus, resorption, mummification, autolysis, stillbirth, birth with clinical symptoms, or birth of clinically healthy but chronically infected ones. The objective of this study was to identify <i>N. caninum</i> infection in aborted bovine fetuses through molecular analysis and mouse bioassay testing. From 2019 to 2022, a total of 121 bovine aborted fetuses were collected from dairy farms in Khorasan Razavi province. Fetal brain samples were screened for detection of the parasite DNA using polymerase chain reaction assay (PCR). Additionally, a portion of PCR-positive brain tissue was homogenized and inoculated into the peritoneum of five BALB/c mice. All mice were sacrificed six weeks post -infection and examined using serology, microscopy and PCR methods. If the mice's brain samples tested PCR -positive, the mouse bioassay test was repeated two times. The <i>N. caninum</i> DNA was detected in 19.8% of brain samples in bovine aborted fetuses. Among PCR-positive brain samples, only ten samples were suitable for mouse bioassay examination. All inoculated mice remained seronegative and showed no clinical signs after three rounds of bioassays, although PCR testing of the brain samples of three mice groups were PCR-positive after repeated bioassays. The PCR results showed a moderate frequency of <i>N.caninum</i> infection in aborted bovine fetuses. Furthermore, the isolates obtained in this study demonstrated low pathogenicity in BALB/c mice, suggesting that they belong to an avirulent strain.