Evaluation of a Canine Adenovirus Type 2 Strain as a Replacement for Infectious Canine Hepatitis Vaccine

Abstract

SUMMARY A modified live strain of canine adenovirus type 2 (CAV-2) was developed and evaluated as a replacement for infectious canine hepatitis (canine adenovirus type 1; CAV-1) vaccines. In a genetic stability test, the vaccine strain remained nonpathogenic through five back passages in dogs and when given by the intranasal route. Following necropsy of 16 vaccinated dogs, gross and microscopic lesions characteristic of CAV-2 infection were not observed. Results of virus isolation tests for various tissues from the same dogs were negative except for low viral infectivity titers for tonsillar tissue from two dogs and bronchial lymph nodes from one dog. Ninety seronegative dogs remained clinically normal following iv inoculation with the CAV-2 vaccine strain. Of 37 control dogs inoculated with a CAV-1 vaccine strain, 8 (21.6%) developed postvaccination ocular lesions. In an immunogenicity test, 20 vaccinated dogs remained clinically normal following CAV-1 challenge that killed all five susceptible control dogs. A second group of 20 vaccinates remained clinically normal following CAV-2 challenge that clinically affected all five susceptible control dogs. Postchallenge necropsy findings and results of virus isolation tests for tissues from the 40 vaccinates were negative. The vaccine strain (in various combinations with canine distemper and canine parainfluenza vaccine and Leptospira bacterin) was evaluated for safety in 19,323 dogs vaccinated by private practitioners. A total of 170 reactions, most of them minor and transient, were reported. Ocular lesions attributable to vaccination were not reported.