Comparative investigation of tissue alterations and distribution of BVD-viral antigen in cattle with early onset versus late onset mucosal disease.

Tissue alterations and distribution of BVDV antigen were examined in nine cattle with early onset and five cattle with late onset mucosal disease (MD) to evaluate the possibility to differentiate between the two disease entities. MD was induced by inoculation of persistently viremic cattle with different strains of cytopathogenic BVDV. Animals which developed early onset MD became moribund approximately 2 weeks post-inoculation (pi); animals with late onset MD 42-115 days pi. All animals were euthanized and necropsied when moribund. Macroscopic lesions were found in the upper and lower digestive tract of cattle with early and late onset MD. In cattle with late onset MD, lesions in the oral cavity were generally milder and in the intestinal tract they were not only associated with GALT, but frequently affected the mucosa outside. Histologically, the abrupt changes between hyperplastic and atrophic areas of mucosa were striking in the cattle with late onset MD. This corresponded with the multifocal distribution of areas of mucosa in which intense staining for BVD-virus antigen could be demonstrated. In both courses of MD, a severe depletion of Peyer's patches was noted, but only in late onset MD, there was a complete loss of architecture. The most distinctive difference was the presence of vascular lesions which were observed in all five cattle with late onset MD, but in none of the animals with early onset MD. The vasculopathy was characterized by segmental necrosis of vascular walls and lymphohistiocytic perivasculitis in arterioles and small arteries in the submucosa of the intestine.