Bovine viral diarrhea virus outbreak in a beef cow herd in South Dakota

Authors: KANE, SUSAN - South Dakota State University; HOLLER, LARRY - South Dakota State University; BRAUN, LYLE - South Dakota State University; Neill, John; YOUNG, DOUGLAS - South Dakota State University; Ridpath, Julia; CHASE, CHRISTOPHER - South Dakota State University

Submitted to: Journal of the American Veterinary Medical Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2015
Publication Date: 6/15/2015
Publication URL: http://handle.nal.usda.gov/10113/61232
Citation: Kane, S.E., Holler, L., Braun, L.J., Neill, J.D., Young, D.B., Ridpath, J.F., Chase, C.C. 2015. Bovine viral diarrhea virus outbreak in a beef cow herd in South Dakota. Journal of the American Veterinary Medical Association. 246(12):1358-1362. DOI 10.2460/javma.246.12.1358.

Interpretive Summary: Bovine viral diarrhea viruses (BVDV) are pathogens of cattle. Infection of pregnant cows with BVDV can result in the infection of fetus that she is carrying. Infection of fetuses with BVDV can have a number of different results including death of the fetus, congenital defects, failure to thrive followed by neonatal death and the birth of calves persistently infected with BVDV. This report is the summary of an outbreak of BVDV in a herd of 136 pregnant heifers. The introduction of a single strain of BVDV into this herd resulted in a spectrum of clinical presentations in calves including fetal death, poor thrift, persistent infection, mucosal disease like lesions and clinically normal animals. BVDV was detected in 44 out of 128 live calves born to this herd. Of these, 28 died in the first year of life, 2 were euthanized due to poor condition and 11, while persistently infected, appeared clinically normal and were sold for slaughter at one year of age. The number of PI calves resulting from this outbreak allowed the comparison of outcomes on a scale not previously available.

Technical Abstract: The objective of this study was to describe the outcome of natural bovine viral diarrhea virus (BVDV) infection in a herd of 136 bred heifers. This outbreak was notable in that a total of 36 PI calves were generated. Of the 136 bred heifers, 8 failed to deliver a calf. Eight calves died shortly after birth. Of the remaining 120 calves, nine of the calves exhibited lesions consistent with congenital BVDV infection. However, a total of 44 out of 120 (36.7%) calves tested positive for BVDV by ear notch testing. Five of these calves died following weaning. Testing of a second earnotch samples and virus isolation from blood revealed that 36 animals tested BVDV positive and 3 tested negative indicating that at the time of the first testing 36 calves were persistently infected (PI) and 3 calves were transiently infected (TI). The 5 BVDV positive animals that died before the second testing and the confirmed PI and TI animals were infected with highly similar BVDV Type 2a strains suggesting that the outbreak was due to the introduction of one strain of BVDV. Serum neutralization assays detected titers against BVDV1 and 2 in the 3 TI calves and 9 of the confirmed PI calves. Titers were considerably lower in serum from the PI calves compared to titers in the serum of the 3 TI calves. Titers in the PI calves declined over a six month time period suggesting that the observed titers may have been the result of passive immunity transferred prior to weaning. Of the 9 PI animals with low titers, 7 developed mucosal disease and died suddenly in the year following the outbreak, and two were euthanized due to prolonged ill thrift. Of the 19 PI calves without detectable serum titers against BVDV, 11 appeared clinically normal and were sold for slaughter and 8 between weaning and one year of age. Both PI and TI calves (n = 44) weighed significantly less at birth and 3 months of age than co-hort calves that tested negative for BVDV. In summation, BVDV was detected in 44 out of 128 live calves born to this herd. Of these, 3 were transiently infected, 28 died (5 shortly after weaning in August, 2004, and 23 in April through August, 2005), 11 were sold for slaughter at one year of age, and 2 were euthanized. The 23 calves that died in 2005 were necropsied and 17 of these animals were found to have mucosal disease lesions. Follow-up surveillance of the cow herd indicated that the cow herd was PI negative and that all PI animals had been removed and subsequent tests of the herd for BVDV were negative. The number of PI calves resulting from this outbreak allowed the comparison of outcomes on a scale not previously available. The introduction of a single strain of BVDV into a naïve herd resulted in a spectrum of clinical presentation including reproductive loss, poor thrift, mucosal disease like lesions and clinically normal animals. Finally, since three BVDV ear notch positive animals were transiently infected, this study reinforces the importance of performing two PI tests prior to confirming a diagnosis of persistent infection.