Multifocal hepatic necrosis in a bovine fetus (IBR, BHV-1)
History: Two aborted bovine fetuses were submitted. One had been partially scavenged, the other was intact. The herd was vaccinated with a modifed live IBR vaccine. There are 24 heifers in the herd and 6 have aborted at the same time.
Gross Lesions: None, the placenta was not submitted
Most tissues were autolyzed severely. One fetus had no lesions, the other had the following:
Liver: There are multifocal random areas of hepatocellular necrosis surrounded by intact hepatic parenchyma. The necrotic areas are characterized by loss of hepatic cord and sinusoidal architecture with cellular and karyorrhectic debris with no associated inflammation.
Lungs: There are small fragments of meconium in multifocal alveoli scattered throughout the lung.
Aerobic culture (Lung, liver, stomach contents): Streptococcus zooepidemicus, Aeromonas sp, Streptococcus sp (Alpha hemolytic), and Staphylococcus sp (Non-hemolytic).
Multifocal hepatic necrosis is commonly caused by IBR (BHV-1). Virus isolation and FA tests were both negative for IBR, but false negative results can occur if the fetus is cold or frozen before submission, or if there is significant time between death and submission. Vaccination of pregnant cows with modified live vaccines can result in fetal infection and abortion despite previous vaccination of the cows.
We interpreted the bacterial cultures as post-mortem contaminants. The other fetus was pretty much useless for diagnosis. The presence of meconium in the lungs is generally attributed to fetal distress (hypoxia) in utero resulting in release of meconium and aspiration of amniotic fluid with meconium.