Determination of protection provided by two modified live bovine herpesvirus-1 vaccines against bovine herpesvirus-1 conjunctivitis in calves

Abstract

A study was performed in 2 phases to determine the ability of 2 different modified live (MLV) bovine herpesvirus-1 (BoHV-1)
vaccines to protect against conjunctivitis caused by a recent field isolate of BoHV-1. In phase I, BoHV-1 isolates were used to
determine the ability of the isolates to cause conjunctivitis and to establish a challenge model for phase II. Fifteen calves were
randomly assigned to 1 of 3 groups: 5 calves received 5 mL containing 107 tissue culture infectious dose (TCID)50/mL of BoHV-1
adminisered intraocularly (topically) for 2 days, 5 calves received 5 mL of inoculum consisting of 107
TCID50/mL of BoHV-1 administered intranasally for 2 days, and 5 calves served as unchallenged sentinels and received phosphate
buffered saline, 5 mL administered by the intranasal and 5 mL by the intraocular route for 2 days. All 15 calves developed
pyrexia (rectal temperature greater than 103.5°F (39.7°C)), were BoHV-1 virus isolation positive from ocular swabs
and 10/15 calves had increased ocular discharge and conjunctivitis. In phase II, 10 calves were intranasally vaccinated with
a MLV BoHV-1, 10 calves were parenterally vaccinated with a MLV BoHV-1, and 5 calves were unvaccinated. All 25 calves
were challenged by receiving 5 mL ntraocularly of 107 TCID50/mL of BoHV-1 for 2 consecutive days. Following challenge, calves were examined daily, and blood (serum), nasal swabs, and conjunctival swab samples were obtained on study days 0, 3-7, 10, 14 and 28. Both vaccines significantly decreased post challenge ocular lesions, clinical scores, and quantity of virus isolated.