THE DIAGNOSIS OF WESSELSBRON-DISEASE IN A NEWBORN LAMB BY IMMUNOHISTOCHEMICAL STAINING OF VIRAL-ANTIGEN

Wesselsbron disease (WSL) was diagnosed in a 2-d-old lamb on a farm in the north-eastern Free State Province where a few abortions and neona tal deaths occurred in sheep in April 1994. The liver of the lamb was slightly swollen and orange-brown and, microscopically, it revealed si ngle or small groups of necrotic hepatocytes that were randomly scatte red throughout the lobules. Other histopathologic hepatic lesions incl uded the presence of acidophilic bodies, intranuclear inclusion bodies in a few hepatocytes, neutrophils in the parenchyma, mild Kupffer-cel l and bile-ductular proliferation and infiltration of mixed inflammato ry cells in the portal tracts. Immunohistochemical staining of section s of formalin-fixed specimens of the liver with polyclonal antibody ag ainst WSL virus revealed positive staining in acidophilic bodies, cyto plasmic fragments of necrotic: liver cells, the cytoplasm of degenerat ed hepatocytes and, rarely, in intranuclear inclusions. Positive stain ing was also obtained in liver sections from two newborn lambs experim entally infected with WSL virus. The results of this investigation sho wed that the immunohistochemical staining of sections of formalin-fixe d liver can be used to confirm the diagnosis of WSL in new-born lambs.