Neosporosis (caused by Neospora caninum) was first discovered in New Mexico in 1989 when there was an abortion outbreak on a dairy. Further research concluded that the disease has been around for quite some time, maybe even longer than cattle have been! We had never heard of it before because it had not been identified. Disease lesions (protozoal cysts) are primarily found in the brain and spinal chord of the aborted fetus, although they may also be found in liver and heart tissues. Most veterinarians did not examine the brains of calves at necropsy, so it was not discovered earlier.

The protozoa have primary and intermediate hosts. The primary host is usually a dog, coyote, wolf, or fox. Cattle themselves are the intermediate hosts for the protozoa. It is transmitted when an infected canine sheds the N. caninum oocysts in its feces. Cows become infected when they consume feed that has been contaminated with these oocysts. Once they become infected, they are lifelong carriers.

There is minimal cow-to-cow transmission of the disease, but a pregnant cow can pass the organism in utero to the fetal calf. The fetus can die from the initial infection and be aborted, typically between three and six months of gestation. A number of infected fetuses will be born normal and healthy, but they will be carriers; when they reach maturity, they will probably abort their first and second pregnancies.

The two ways that the protozoa can be transmitted to cows is by 1) ingestion of infective oocysts from dogs and 2) by in utero transmission. Dogs become infected by either consuming infective oocysts or tissue cysts in the aborted fetus and placenta. A very important biosecurity practice for this disease is to prevent dogs from having access to aborted tissues, thereby continuing the Neospora caninum cycle on the farm.

More information on Neosporosis can be found at:
http://ars.usda.gov/Main/docs.htm?docid=11007.