Submitted to: Veterinary Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2010
Publication Date: 7/1/2010
Citation: Porter, B.F., Ridpath, J.F., Calise, D.V., Payne, H.R., Janke, J.J., Baxter, D.G., Edwards, J.F. 2010. Hypomyelination Associated with Bovine Viral Diarrhea Virus Type 2 Infection in a Longhorn Calf. Veterinary Pathology. 47(4):658-663. Interpretive Summary: Infections with bovine viral diarrhea viruses (BVDV) are the source of significant economic losses to cow/calf producers. These losses are primarily the result of infection of the fetus. There are many outcomes that result from fetal infection. These include death of the fetus, persistent life long BVDV infection and birth defects (also known as congenital defects). This manuscript describes a novel congenital defect observed in a newborn calf that resulted from a BVDV fetal infection. This animal was unable to rise, exhibited poor balance and generalized tremors. Microscopic examination revealed a reduction in the insulating material that surrounds nerves. This material is known as the myelin sheath. The myelin sheath is essential for proper functioning of the nervous system. Reduction in the myelin sheath is called hypomyelination. Hypomyelination has been reported in most domestic animals. Most commonly it is attributed to a genetic mutation. This study demonstrates that hypomyelination may also be the result of a viral infection of the fetus.
Technical Abstract: A newborn Longhorn heifer calf presented to the Veterinary Medical Teaching Hospital at Texas A&M University with generalized tremors, muscle fasciculations, ataxia, and nystagmus. At necropsy, gross central nervous system lesions were not observed. Histopathologic evaluation of the brain and spinal cord revealed a mild to moderate, diffuse microgliosis and astrocytosis, and minimal nonsuppurative encephalitis. Myelin stains showed decreased myelin staining, and ultrastructural examination revealed thinning and absence of myelin sheaths. Immunohistochemical stains were positive for BVDV in a variety of cell types. Noncytopathogenic BVDV was isolated from the brain, and phylogenetic analysis identified the strain as BVDV type 2. BVDV-induced hypomyelination is rare and analogous to lesions found in neonates infected with border disease and classical swine fever viruses. This case is the first documentation of hypomyelination in a calf specifically attributed to BVDV type 2 and the first description of the ultrastructural appearance of BVDV-induced hypomyelination.