EFFICACY OF COMMERCIAL VACCINES AGAINST THE PREVALENT STRAINS OF NEWCASTLE DISEASE AND AVIAN INFLUENZA (H9N2) INFECTIONS IN BROILERS IN PAKISTAN

The efficacy of the two commonly used commercial vaccines for Newcastle disease (ND) and low path avian influenza (LPAI) H9N2 were evaluated against field virus in broiler chicks. One hundred one-dayold commercial broiler chicks were divided into four groups (A to D) with an equal number of birds per group. Group A and B were vaccinated against H9N2 and NDV, respectively, at day 7 of age while group C served as positive infected control for H9N2 and group D for NDV. Serum samples from birds in all groups were tested for presence of antibodies against H9N2 and NDV at day 21 of age. Subsequently, on day 28 of age, groups A and C were challenged with the field strain of H9N2 virus, and Group B and D with NDV. Birds were monitored for a period of 2 weeks for development of any clinical signs and mortality. The geometric mean titer were high in groups A (4.90) and B (7.3), and low in the unvaccinated groups C (0.7) and D (1.1). The highest and lowest value of H9N2 antibody titer detected through ELISA were 1.498 and 0.502, respectively. The S/P ratios greater than 0.5 were considered positive. The highest and lowest value for NDV antibody titer detected through ELISA were 783 and 882, respectively. Serum samples with titer greater than 396 were considered positive and indicated vaccination or other exposure to NDV. On histological examination severe congestion, necrosis, degeneration, hemorrhages and leukocyte infiltration were observed in intestine, lungs, trachea and bursa of Fabricius of the non-vaccinated group post-infection. Mild tissues changes were observed in the vaccinated group. It can be concluded from the findings that the commonly used commercial vaccines may provide effective protection against the circulating H9N2 and ND virus in broiler birds by producing protective antibody titer.