Challenge with Bovine viral diarrhea virus by exposure to persistently infected calves: protection by vaccination and negative results of antigen testing in nonvaccinated acutely infected calves.

Calves persistently infected (PI) with Bovine viral diarrhea virus (BVDV) represent an important source of infection for susceptible cattle. We evaluated vaccine efficacy using calves PI with noncytopathic BVDV2a for the challenge and compared tests to detect BVDV in acutely or transiently infected calves versus PI calves. Vaccination with 2 doses of modified live virus vaccine containing BVDV1a and BVDV2a protected the calves exposed to the PI calves: neither viremia nor nasal shedding occurred. An immunohistochemistry test on formalin-fixed ear notches and an antigen-capture enzyme-linked immunosorbent assay on fresh notches in phosphate-buffered saline did not detect BVDV antigen in any of the acutely or transiently infected calves, whereas both tests had positive results in all the PI calves.