PATHOLOGICAL AND VIROLOGICAL STUDIES OF EXPERIMENTAL PARVOVIRAL ENTERITIS IN CALVES

Calves held in isolation showed a progressive decline in maternally derived antibody titers to bovine parvovirus but low concentrations of inhibitors resistant to heat and kaolin treatment persisted as the animals matured. These inhibitors had both hemagglutination inhibition and plaque neutralizing activity and were considered to be of non-specific origin. Following oral challenge with bovine parvovirus, calves developed mild to moderate diarrhea, with lymphopenia and viremia. Sequential virological and immunofluorescent studies showed that the virus initially infected tonsils and intestinal tract, subsequently spreading to systemic lymphoid tissues. Histological and scanning EM examinations revealed moderate small intestinal villus atrophy and fusion due to crypt damage, together with lymphoid necrosis predominantly associated with the intestinal tract and thymus. Although the disease was not very severe, this may have been because the low parasite burden in the animals reduced mitotic activity in susceptible tissues.