FATAL, GENERALIZED BOVINE HERPESVIRUS TYPE-1 INFECTION ASSOCIATED WITH A MODIFIED-LIVE INFECTIOUS BOVINE-RHINOTRACHEITIS PARAINFLUENZA-3 VACCINE ADMINISTERED TO NEONATAL CALVES

Generalized bovine herpesvirus 1 (BHV-1) infection was diagnosed in si x Salers calves from the same herd. The calves had received an intramu scular injection of modified-live infectious bovine rhinotracheitis pa rainfluenza-3 vaccine between birth and three days of age. The purpose of this study was to determine if the outbreak was associated with th e vaccine strain of BHV-1. Analysis of epidemiological data and BHV-1 DNA for restriction fragment length polymorphism was undertaken. Multi focal necrosis in multiple organs was observed on pathological examina tion, and the presence of BHV-1 in tissues was confirmed by immunohist ochemistry. Forty-three calves (aged birth of thirty days) were vaccin ated over an 11-day interval. The 10 deaths recorded for vaccinated ca lves were clustered over a subsequent 14-day interval. Mortality in ca lves vaccinated between birth and three days of age was significantly higher than in nonvaccinated calves (chisquare test; p less-than-or-eq ual-to 0.025), and this mortality was characterized by a greater age a t death and duration of illness for vaccinated calves (t test; p less- than-or-equal-to 0.001). The patterns of the restriction fragments, ge nerated by six restriction endonucleases, of BHV-1 isolated from a nec ropsied calf and from the vaccine were identical, and different from t hat of a laboratory strain of BHV-1 (P8-2). These findings support the conclusion that newborn calves were susceptible to an intramuscularly injected vaccine strain of BHV-1, and that administration of an intra muscular modified-live infectious bovine rhinotracheitis parainfluenza -3 vaccine to neonatal calves may not be an innocuous procedure.