| Abstract: | A canine parainfluenza viral vaccine was developed and shown to be safe by absence of clinical disease in vaccinated dogs and by inability to isolate vaccine virus from blood or nasopharyngeal swabs. Backpassage in susceptible dogs, using blood of vaccinated dogs, could not be demonstrated. The vaccine produced neutralizing antibody when administered either intramuscularly or subcutaneously; however, a significantly higher immune response was obtained by intramuscular inoculation. Differences in the antibody response were not produced by tenfold dilutions of vaccine virus ranging from 10(2.9) to 10(5.9) median tissue culture infective doses. The presence of neutralizing antibody was associated significantly with decreased respiratory shedding period of challenge virus by vaccinated dogs compared to seronegative control dogs. Six days after aerosol exposure to virulent challenge virus, 100% of the controls (n = 5) but only 15% of the vaccinated dogs (n = 3) shed virus. Seven days after challenge exposure, virus could not be recovered from the vaccinated dogs, but 80% of the control dogs shed virus. An anamnestic response occurred in vaccinated dogs but not in the seronegative control dogs following challenge exposure. A mild clinical disease was produced in 3 of the 5 seronegative control dogs but not in the 20 vaccinated dogs. |
