Relationship between degree of viremia and disease manifestations in calves with experimentally induced bovine viral diarrhea virus infection

Objective-To compare degree of viremia and disease manifestations in calves with type-I and -II bovine viral diarrhea virus (BVDV) infection. Animals-16 calves. Procedure-Colostrum-deprived calves obtained immediately after birth were a ssigned to 1 control and 3 treatment groups (4 calves/group). Calves in tre atment groups were inoculated (day 0) by intranasal instillation of 10(7) m edian tissue culture infective dose BVDV 890 (type II), BVDV 7937 (type II) , or BVDV TGAN (type I). Blood cell counts and virus isolation from serum a nd leukocytes were performed daily, whereas degree of viremia was determine d immediately before and 4, 6, 8, and 12 days after inoculation. Calves wer e euthanatized on day 12, and pathologic, virologic, and immunohistochemica l examinations were performed. Results-Type-II BVDV 890 induced the highest degree of viremia, and type-I BVDV TGAN induced the lowest. Virus was isolated more frequently and for a longer duration in calves inoculated with BVDV 890. A parallel relationship between degree of viremia and rectal temperature and an inverse relationsh ip between degree of viremia and blood cell counts was observed. Pathologic and immunohistochemical examinations revealed more pronounced lesions and more extensive distribution of viral antigen in calves inoculated with type -ii BVDV. Conclusions and Clinical Relevance-Degree of viremia induced during BVDV in fection is associated with severity of clinical disease. Isolates of BVDV t hat induce a high degree of viremia may be more capable of inducing clinica l signs of disease. Strategies (eg, vaccination) that reduce viremia may co ntrol clinical signs of acute infection with BVDV.