Effect of concurrent experimentally induced bovine respiratory syncytial virus and bovine viral diarrhea virus infection on respiratory tract and enteric diseases in calves.
OBJECTIVE
To compare experimentally induced concurrent bovine viral diarrhea virus (BVDV) and bovine respiratory syncytial virus (BRSV) infection with single virus infection.


METHODS
9- to 12-month-old calves.


METHODS
Calves were allotted to 4 groups: 1, mock-infected control (n = 3); 2, BRSV infected (5); 3, BVDV infected (5); and 4, concurrent BRSV and BVDV infected (5). Total and differential WBC counting was done. Concentration and duration of BVDV in nasal secretions and serum, and duration of BRSV in nasal secretions were determined. Concentration of BVDV in various tissues was determined, and isolation of BRSV from lung tissue was attempted. Histologic examination and immunohistochemical analysis were done to detect lesions and distribution of viral antigens, respectively.


RESULTS
Calves with concurrent infection developed more severe clinical signs of disease (fever and diarrhea), leukopenia, and more severe lesions. They also shed virus from nasal secretions in greater concentration and for longer duration, and BRSV was isolated from their lungs. Calves with concurrent infection also had more extensive lung lesions. Alimentary epithelial necrosis and severe lymphoid depletion were associated with BVDV infection in calves with or without concurrent BRSV infection. BVDV antigen in lymphatic tissue was detected in stromal cells only.


CONCLUSIONS
Concurrent infection with BRSV and BVDV resulted in more severe respiratory tract and enteric disease than did infection with either virus alone, possibly indicating synergistic effect between the viruses. BVDV's role in causing respiratory tract disease is attributable, indirectly, to effects on the host's immune system, not to infection of the lungs.
Brodersen
B W
BW
Department of Veterinary and Biomedical Sciences, Institute of Agriculture and Natural Resources, University of Nebraska, Lincoln 68583-0905, USA.
Kelling
C L
CL
D000818:Animals; D000956:Antigens, Viral / Q000032:analysis; D001912:Bovine Virus Diarrhea-Mucosal Disease / Q000150:complications*; D002417:Cattle; D002418:Cattle Diseases / Q000821:virology*; D001908:Diarrhea Viruses, Bovine Viral; D004751:Enteritis / Q000150:complications / Q000662:veterinary* / Q000821:virology; D007150:Immunohistochemistry; D007958:Leukocyte Count; D008168:Lung / Q000821:virology; D018357:Respiratory Syncytial Virus Infections / Q000150:complications / Q000662:veterinary*; D018112:Respiratory Syncytial Virus, Bovine; D017201:Virus Shedding
D000956:Antigens, Viral