A comparison of immune response and Fabricius bursa index in vaccinated and unvaccinated Japanese quails following experimental infection with an Iranian virulent isolate of Newcastle disease virus

Newcastle disease (ND) is one of the most contagious and fatal viral diseases which infects many bird species, including the Japanese quail. This study was aimed to evaluate the effect of experimental infection with virulent Newcastle disease virus (NDV) on immune response against the virus as well as on the relative weight of bursa of Fabricius in vaccinated and unvaccinated Japanese quails. A total of 160 one-day-old quails were allocated to 4 groups, including a vaccinated and challenged group (1), an unvaccinated and challenged group (2), a vaccinated and unchallenged group (3), and an unvaccinated and unchallenged group (4). The birds were raised under the similar conditions. Vaccination was done on the 20th day with live vaccine B1 strain (Razi Vaccine and Serum Research Institute, I.R.Iran) via eye drop and the challenge by Newcastle disease virus (NDa: KP347437) was induced via eye drop on the 34th day. Blood samples were collected for serological assessments (HI) and the bursa of Fabricius was weighed after autopsy at different time periods. The first postvaccination serological change was observed in group 3 twenty-one days after vaccination while the first post-challenge serological change was detected in groups 1 and 2 one week after the challenge induction. The same three groups also showed significant increments in the serum NDV-specific antibody titer in the subsequent weekly samplings. The antibody titer in group 4 was zero throughout the experiment. Regarding the relative weight of bursa, the only statistically noticeable change was observed within group 2 where the samples taken on the 5th day were significantly heavier than those collected on the 9th and 14th days. The results of this study showed that a single vaccination of quails with B1 strain, in the absence of maternal antibody, could provide a good protection against virulent NDV. With due attention to the Newcastle disease status in Iran, at least once vaccination is recommended during the rearing period of quails.