Molecular detection of Neospora caninum in the placenta and blood of postparturient cows and their full-term precolostral calves.

Neospora caninum is a major cause of abortion and neonatal mortality in cattle worldwide. While vertical transmission is considered the primary route of infection, the precise relationship between maternal parasitemia, placental infection, and congenital transmission remains unclear. This study aimed to investigate the associations between maternal serological and molecular status, placental infection, and neonatal infection in precolostral calves to better understand the mechanisms of vertical transmission. A cross-sectional study was conducted on 53 postparturient clinically healthy Holstein cows and their full-term precolostral, clinically healthy calves from a large dairy herd in Qazvin Province, Iran. Blood samples were collected from both dams and calves immediately after birth, prior to colostrum intake. Placental tissue was sampled from the caruncle-cotyledon junction. N. caninum-specific antibodies were detected by indirect ELISA, and parasite DNA was identified in buffy coat and placental tissues using conventional and nested PCR targeting the NC5 gene. Associations were analyzed using chi-square tests, odds ratios (OR), and Phi coefficients. Overall, 38% (20/53) of dams and 23% (12/53) of precolostral calves were infected. The vertical transmission rate among infected dams was 60%. Maternal infection (by ELISA or PCR) and placental PCR-positivity were significantly associated with calf infection (OR = 21.6-45.4, P-value < 0.001). Significant associations were observed between dam and calf PCR results (φ = 0.63) and between dam and calf ELISA results (φ = 0.52). Kappa analysis showed good agreement between ELISA and PCR in both dams (κ = 0.69) and calves (κ = 0.68). Findings suggest that vertical transmission of N. caninum is substantial and significantly associated with maternal and placental infection status. However, both ELISA and PCR are reliable tools for identifying at-risk animals; their simultaneous use may enhance diagnostic accuracy in control programs.