In herds with an endemic pattern of abortion, cows infected with N. caninum typically have a 2 to 3-fold increased risk of abortion compared to their seronegative herdmates. Neospora positive cows in herds experiencing an abortion epidemic due to Neospora caninum may have a 20 to 50-fold increase in abortion risk. Neospora caninum is genetically related to Toxoplasma gondii , and a similar life-cycle including a definitive host such as cats, dogs, rodents, or birds, has been proposed but not demonstrated. Direct contact with infected fetal tissues has also been postulated as a potential source of postnatal N. caninum infection. In the same study, transmission via milk or colostrum was considered highly unlikely based on lack of seroconversion in heifers less than 10 months of age.
Congenital infection appears to have no detrimental affect on calf health.
Clinically inapparent infection appears to persist for the life of congenitally-infected animals. Neospora infection in cattle has been reported from virtually all regions of the United States, as well as all countries that have performed serologic or necropsy-based surveillance for the agent. Prospective studies of fetal survival in Neospora seropositive dams suggest that most abortion occurs between 3 and 6 months in first gestation heifers, and the window for abortion becomes narrower and later for subsequent pregnancies. Unlike most other infectious agents, cows do not need to be exposed during gestation to abort, and cows that have aborted due to N. caninum may abort due to N. caninum in subsequent pregnancies. Other than abortion, there are no obvious clinical signs of disease in Neospora infected cows.