Example of severe deformity of mandible observed in case #2 Case #2 — Late-term abortions and severe skeletal deformities
BVD reproductive losses are usually associated with early-term abortions. However, in case #2, the clinical presentation was lateterm abortions, preterm calves and congenital defects. Further, the skeletal deformities observed following BVD fetal infections are rarely as severe as those seen in this case, worked up by Patricia Blanchard, of the California Animal Health and Food Safety Laboratory, University of California- Davis. The outbreak occurred in a group of 37 first-calf heifers. At 1 week of age these heifers had been vaccinated with a killed vaccine. From 5 months to 12 months of age these heifers were housed at heifer ranch A. No vaccinations were given at ranch A.
At 12 months of age they were moved to heifer ranch B. Heifer ranch B also housed heifers from three other dairies. A second dose of killed vaccine was delivered at arrival at ranch B. The heifers were six- to seven-months pregnant when they were returned to the home dairy. Approximately eight weeks before the onset of abortions in the heifers, an outbreak of pyrexia and diarrhea was observed in postpartum cows in the herd. Over a four-week period in May 2004, 19 out of 37 heifers aborted or gave birth two to four weeks early. In the first week of the outbreak, seven heifers delivered seven either stillborn or premature live calves that had severe deformations including notably shortened mandibles.
One calf had particularly severe congenital defects including absence of forelimbs, cleft palate and no bone covering the dorsal central 9 cm of the brain. Tissues from four of the calves were submitted for testing. BVDV infection was confirmed in all four calves. Phylogenetic analysis, conducted at the National Animal Disease Center, identified the virus as a BVDV1 strain. Experimental infection of calves with this virus resulted in a more pronounced clinical presentation than that typically observed with BVDV1 strains. The clinical presentation included pyrexia, leukopenia and thrombocytopenia. Experimental infection of fetuses in the first trimester of pregnancy led to persistent infection but not fetal deformities. It may be that the congenital deformities observed were due to infections that occurred later in gestation.
Longitudinal sections of spinal cord stained with Weil’s stain, which is a stain for myelin. One is from a control calf and the other is a longhorn calf infected with BVDV showing hypomyelination. Case #3 — Congenital tremor
BVD in utero can result in morphologic defects in the CNS. Grossly observable congenital neural abnormalities such as cerebellar hypoplasia, hydranencephaly, internal hydrocephalus, microencephaly and proencephaly are commonly associated with BVD. Due to recent reports, we are now beginning to realize that such gross abnormalities may be only the tip of the iceberg and that defects that can only be observed microscopically may play a bigger role than previously thought. A 2009 paper in the Veterinary Record reported an association between BVD and congenital tremor. This study was based on characterization of 23 different outbreaks of neurological disease in England and Wales occurring between 1991 and 2007. The most common clinical presentation was tremor apparent in calves from birth.