CHANGES IN LEVELS OF VIREMIA IN CATTLE PERSISTENTLY INFECTED WITH BOVINE VIRAL DIARRHEA VIRUS

Virus isolation and serum neutralizing antibody titers were determined over a period of time from samples collected from animals persistentl y infected with bovine viral diarrhea virus (BVDV). To evaluate over t ime the ability to detect BVDV by virus isolation from serum or white blood cell preparations, 4 persistently infected calves were monitored from birth until 70 days of age. In 3 of 4 persistently infected calv es, virus isolation from serum and white blood cells was negative unti l approximately 42 days of age, when colostral antibody had declined. The level of viremia in 7 adult (>12 months) persistently infected ani mals decreased by 1 10-fold dilution over at least a 2-year period. Th e level of viremia became undetectable by virus isolation from serum i n 1 of the 7 animals examined. This decline was associated with the de velopment of virus neutralizing antibody. Although the level of viremi a is fairly stable within persistently infected animals, the presence of specific neutralizing antibody may affect the ability to isolate BV DV. These findings are important when considering diagnostic testing t o identify persistently infected animals by virus isolation.