Efficacy of a Deletion Mutant Bovine Herpesvirus-1 (BHV-1) Vaccine That Allows Serologic Differentiation of Vaccinated from Naturally Infected Animals

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Abstract
Fifteen bovine herpesvirus-1 (BHV-1)-negative calves were vaccinated intramuscularly with 107.4 plaque-forming units of a double-deletion BHV-1 mutant (IBRV(NG)dltkdlgIII), and 6 remained as nonvaccinated controls. Thirty days after vaccination, the animals were challenged by nasal instillation of 108.2 CCID50 of a virulent BHV-1 strain (Cooper). The vaccinated calves were protected against wildtype virus challenge as demonstrated by clinical evaluation. Most of the vaccinates developed only a mild rhinitis (lasting an average of 6.5 days) with almost no systemic symptoms, whereas the controls developed a serious illness characterized by rhinitis (X = 11.5 days), conjunctivitis, hyperthermia, apathy, loss of appetite, and dyspnea. The vaccinates also shed significantly less virus and for a shorter period of time (X = 5.5 days) than the controls (X = 9 days). Thirty days after vaccination, the vaccinates were negative in an anti-gIII specific blocking enzyme-linked immunosorbent assay (ELISA), despite the fact that most of them had developed neutralizing antibodies (serum neutralization titers ranging from 1:2 to 1: 16). Seroconversion to gIII was detected as early as 7 days postinfection (dpi). Fourteen days after the challenge, all the animals exposed to wildtype BHV-1 had developed anti-gIII antibodies and were positive in this differential serologic test. Six controls plus 8 vaccinates kept in isolation were still positive to gIII when tested at 75 dpi. The use of the IBRV(NG)dltkdlgIII strain in conjunction with an anti-gIII specific blocking ELISA kit represents a powerful tool for BHV-1 control/eradication programs.

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