EFFECT OF ACUTE INFECTION WITH NONCYTOPATHIC OR CYTOPATHIC BOVINE VIRAL DIARRHEA VIRUS ISOLATES ON BOVINE PLATELETS

A total of 21 calves were inoculated IV with 1 of the following isolat es of bovine viral diarrhea virus (BVDV); CD87 (n = 10), NY-1 (n = 3), NADL (n = 5), or were sham-inoculated with virus-free medium (n = 3). Subsequent to inoculation, platelet counts were monitored to detect d ifferences between noncytopathic (CD87, NY-1) and cytopathic (NADL) is olates in their ability to induce thrombocytopenia. Platelet count dec rease throughout infection was statistically analyzed by comparing the slope of the line drawn from the count on the day of infection to the lowest count achieved by that calf. Significant difference was observ ed in the CD87-inoculated calves and in the NY-1-inoculated calves, co mpared with those of the same control group. Significant difference wa s not observed in the slope of platelet count decrease between the cyt opathic NADL-infected calves and control-group calves. The data indica te that noncytopathic BVDV isolates may more easily induce thrombocyto penia than do cytopathic isolates in immune-naive, immunocompetent cal ves; acute infection with 1 cytopathic BVDV isolate (NADL) did not ind uce thrombocytopenia. In addition, although each calf seroconverted, v irus was rarely isolated from mononuclear cells obtained from calves w ith cytopathic infections. At some point after infection, virus was al ways isolated from each of the calves undergoing noncytopathic infecti ons, and occasionally, transient association of noncytopathic BVDV ant igen with platelets was observed during these infections.