The Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) performs fetal necropsies on a variety of species in order to determine cause of death and cause of abortion. For beef and dairy cattle raisers, this process is key to help prevent future losses in situations where there is a greater than 3-5% loss per month or per year.
Neospora caninum, a unicellular protozoan parasite, is a common cause of fetal death and abortion in cattle in Texas. Economic losses stem from early fetal death, neonatal death or stillbirth, increased calving interval, increased culling, decreased milk production and reduced value of breeding stock. The Neospora parasite sheds oocysts (eggs) in the feces of infected dogs and coyotes. It infects cattle by two routes: dog-to-cattle and cow-to- fetus. Cattle become infected by ingesting feed, water or pasture grass contaminated by the oocysts. Many cows can be infected simultaneously resulting in “abortion storms.” Cow-to-fetus transmission occurs during parasite reactivation in a previously infected cow or by new infection of a pregnant cow. Infected heifers can transmit Neospora to their offspring during subsequent pregnancies. In this manner, Neospora can be maintained in a herd for multiple generations.
An aborted Holstein fetus from a dairy herd suspected to be infected with Neospora was submitted to TVMDL for necropsy. The fetus was estimated to be 4-5 months gestational age. The carcass was moderately autolyzed. Tissues were negative by PCR test for Bovine Viral Diarrhea virus (BVDV) and Leptospirosis. A culture of stomach contents was negative for Trichomonas, Campylobacter and Brucella. Histologic evaluation of the heart and brain revealed mild, multifocal lymphoplasmacytic myocarditis and nonsuppurative encephalitis, respectively. One of the brain lesions contained multiple tachyzoites consistent with Neospora. This diagnosis was confirmed by a positive PCR test performed on brain tissue. This was an unusual finding in that the inflammation and tissue destruction are usually seen without the organism being readily apparent.
Neospora can cost cattle producers thousands of dollars per year. While a necropsy on a fetus is costly, determining the underlying cause of a cow’s abortion or calf’s death will pay off in the long run. For information on TVMDL’s Neospora-finding diagnostic services, visit tvmdl.tamu.edu.