抄録
Chickens 32 days old were vaccinated with the Hitchner B1 strain of Newcastle disease virus through the drinking water under field conditions. They were examined for the immune response and safety.
1. Chickens vaccinated with 106.2 EID50 failed to show any sympotm of respiratory disturbances.
2. After a single vaccination, the geometric mean HI titer (GMT) rose significantly to 36.3 within 6 weeks. It declined rapidly, reaching 3.6 6 months after vaccination. Similar results were obtained from chickens revaccinated at 62 days of age. Of chickens vaccinated with a single or two doses, 80 to 100 per cent resisted to intramuscular challenge with 104.7 EID50 of virulent virus of the Sato strain over a period from 2 to 6 months after vaccination. Their immunity began to decrease 4 months after vaccination gradually. Chickens revaccinated at one-month interval exhibited a little better resistance to challenge than those given a single vaccination dose.
3. In chickens revaccinated 1, 2, and 3 weeks, 1 and 2 months after the first inoculation HI GMT showed no sgnificant rise. All the chickens resisted to challenge made 3 weeks later.
4. Chickens given the third vaccination dose 6 months after the second vaccination showed a higher HI antibody response than chickens inoculated with inactivated vaccine.
5. Of susceptible chickens put in contact with chickens inoculated with live virus, vaccine 43 to 80 per cent were infected after 5 to 10 days. Noinfection occur red among those chickens after 15 to 20 days.
