Infectious bovine rhinotracheitis virus-induced abortion

Abstract

History and Clinical Signs : Abortion “storms” are common with 60% and possibly more of the cows in a herd aborting. Signs of other syndromes produced by the infectious bovine rhinotracheitis (IBR) virus may or may not be present in the herd. Gross Lesions : Pre-expulsion autolysis of fetal tissues is consistently found. There are no significant gross lesions of the fetus or placenta. Microscopic Lesions : Focal necrosis of the parenchymatous organs, especially the liver, is a consistent lesion. In the absence of other infectious agents, the presence of this lesion is highly significant. Cultural Procedures : IBR virus may be isolated from approximately 1 or 3 fetuses and placentas aborted due to IBR. The virus is isolated most consistently from the placenta. Serologic Procedures : A 4 fold increase in serum neutralization titer to IBR in the second of paired samples (the first taken at the time of abortion and the second 10 days to 2 weeks later) provides evidence of a recent IBR infection and presumptive evidence that IBR was the cause of the abortion. Special Procedures : The fluorescent antibody (FA) technique applied to frozen tissue sections, preferably kidney, has proven to be an accurate diagnostic procedure. Preferred Diagnostic Methods : 1. 1. Demonstration of specific focal fluorescence in frozen sections of tissues from the aborted fetus stained with fluorescein-isothiocyanate-labeled anti-IBR globulin. 2. 2. Demonstration of the presence of typical microscopic foci of necrosis in the fetal parenchymatous organs, especially the liver, and the absence of other significant infectious agents. 3. 3. Isolation of the IBR virus from the fetal or placental tissues. 4. 4. Demonstration of at least a 4 fold rise in the IBR serum neutralization titer in the second of 2 blood samples from the aborting dam, one sample taken at the time of abortion and the other 10 days to 2 weeks later.