Bovine Abortion Diagnostics find BVD
By Jessie Monday, DVM, MS
With over 800,000 tests run annually, TVMDL encounters many challenging cases. Our case study series will highlight these interesting cases to increase awareness among veterinary and diagnostic communities.
A veterinarian was called in to investigate the cause of abortion in a group of 60 well-managed 2-year-old brangus heifers. Four heifers aborted before the investigation was initiated. The herd is closed with a reportedly good biosecurity program and good nutrition. All of the animals are well-vaccinated. A fresh mid-term female fetus and fetal tissues from the fifth abortion were submitted to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) along with blood and serum from the heifer that aborted.
No diagnostically specific lesions were found on necropsy or histopathology. The Bovine Abortion Panel: Fetal Tissues was ordered on the fetal tissues. No pathogenic bacteria were isolated on culture. Vitamin A testing showed acceptable levels of vitamin A in the fetal liver. Neospora caninum, bovine herpesvirus type 1 (BHV-1), and Leptospira spp. were not detected via PCR. Bovine viral diarrhea virus (BVDV) was detected via PCR of the fetal tissues with a Ct value of 18.70. The cutoff Ct value for a positive BVDV PCR sample is <37.00. Bovine Comprehensive Abortion Serology was requested on the dam serum sample at the start of testing as well. Antibody testing was negative for Brucella abortus, Histophilus somni, Neospora caninum, and 5 serovars of Leptospira spp. There was a low (8) virus neutralization (VN) antibody titer to BHV-1. The BVD VN titers were BVD 1a (2048), BVD 1b (≥4096), and BVD 2 (2048). Further investigation revealed that there were severe respiratory problems in this herd about 2 years ago. Based on this history and the evidence provided by the fetal tissue PCR and the maternal serology, the veterinarian instigated a BVD pooled ear notch screening program to find a suspected persistently infected (PI) animal in the heifer herd.
Bovine viral diarrhea virus is a common and widespread virus that is spread most commonly by respiratory secretions and feces. The virus can cause a wide range of clinical syndromes. If a susceptible animal is infected, they may not show any clinical signs, they may show signs of short-term respiratory illness, or they may develop long-term problems due to secondary infections and complications because of immunosuppression. Most cattle infected by BVDV are only infected transiently (TI) and will shed the virus in the environment for a few days or weeks. Animals with long-term problems can shed the virus for more than a month. If a susceptible pregnant brood cow or heifer is exposed to BVDV, she may terminate the pregnancy, give birth to a nonviable abnormal calf, give birth to a weak calf, give birth to a normal calf, or give birth to a calf that is persistently infected (PI) with BVD virus. PI calves are permanently infected with BVDV and shed the virus into the environment. PI calves rarely live more than 2 years due to complications associated with the persistent viral infection. PI calves also excrete more virus into the environment than transiently infected animals, so the risk to other animals in contact with them is high. A PI animal within a herd can have a marked impact on herd production due to abortions, weak non-productive or non-viable calves, and death due to immunosuppression and susceptibility to other diseases. BVD control requires good biosecurity, vaccination, testing, and removal of any PI animals. BVD PCR and antigen capture ELISA are very sensitive tests for screening for BVDV infected animals. Herds with good biosecurity and annual vaccination programs may elect to only test the newborn calves and open cows and heifers annually to screen for BVDV.
To learn more about this case, contact Dr. Monday, bovine veterinary diagnostician at the Amarillo laboratory. For more information on TVMDL’s test catalog, visit tvmdl.tamu.edu.