Efficacy of a Live Newcastle Disease Vaccine against a Genotype Vil Velogenic Viscerotropic Newcastle Disease Challenge
WONG Siam Yit, LIAO Guo-An, TOH Pei Ling, SAINT-GERAND Anne-Lise, LEE Michael, LEMlERE Stephane,YIP Karen
This study evaluates the efficacy of a vaccine (A VI NEW strain) against a genotype VIl velogenic viscerotropic Newcastle disease (vvND) virus isolated from an outbreak in a broiler farm experiencing almost 100% mortality in vaccinated flocks. The live vaccine strain is avirulent and has bath enteric and respiratory tropisms in chickens where it is used commercially as a live vaccine. SPF birds were divided into 6 treatment groups. Group 1 received a single dose of live vaccine at day old by coarse spray. Group 2 received a day old vaccination similar to Group 1 but this was followed by a second single dose at day 11 by eye drop. Group 3 at day old was given a one third dose (0.1 ml) of a killed oil vaccine based on the Ulster 2C strain (genotype 1) subcutaneously together with a single dose of live vaccine by coarse spray. Group 4 had an identical day old vaccination as the Group 3 but in addition was given a booster single dose of live vaccine at 11 days of age via the eye drop route. Group 5 received a single dose of live vaccine at day old by coarse spray. This was followed by a one third dose (0.1ml) of the ki lied oil vaccine given subcutaneously at day S. At day 11, the birds received a booster single dose of live vaccine via eye drop. The sixth and final group were designated as positive unvaccinated contrais. Serology by haemagglutination test showed seroconversion in ali vaccinated groups before challenge. At day 21, ali the groups were infected with the challenge virus at 10 5.0 EID 50 per bird and observed for 14 days. Ali the positive contrais birds died within this period. Ali the vaccinated groups (1-5) showed 100% protection against the challenge. None of the birds in the vaccinated groups exhibited any clinical signs or died during the 14 days observation post challenge. Therefore, this study demonstrated that the live Newcastle disease vaccine, with or without a killed vaccine, was efficacious against a genotype VIl vvND challenge.
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