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Stability of Attenuation in Live Avian Pneumovirus Vaccines

Department of Veterinary Diagnostic Medicine, College of Veterinary Medicine, University of Minnesota, 1333 Gortner Avenue, St. Paul, Minnesota 55108

Correspondence: S. M. Goyal, E-mail: goyal001{at}umn.edu

Vaccination is an important means of controlling avian pneumovirus (APV) infection in turkeys. We have reported earlier on the development of attenuated APV vaccines by serial propagation of a field isolate of APV for 41 and 63 passages in cell cultures, named P41 and P63 respectively. To determine the stability of these 2 live vaccines, 6 turkey-to-turkey back passages were given. The P41 was found to revert back to virulence after sixth back passage as evidenced by the development of clinical signs in inoculated birds. In contrast, P63 was found to be stable after 6 back passages. When challenged at sixth back passage level, birds in both vaccinated groups were found to be protected against a virulent challenge of APV. These results indicate that although both P41 and P63 protect against APV, viral attenuation is more stable in P63 than in P41.

Key Words: avian pneumovirus • reversion • vaccine