Comparative Immunological Study between the Efficacy of Bivalent Inactivated H5N1-ND and Baculovirus Expressed H5N1-ND Inactivated Vaccine (BEST) in Broiler Chickens

Outbreaks of highly pathogenic avian influenza H5N1 (HPAIH5N1) virus have been observed in the commercial poultry industry. The use of inactivated vaccines to control it is widely used. This work was planned to compare the efficacy of conventional bivalent inactivated H5N1-ND and Baculovirus Expressed H5N1-ND (BEST) vaccine in protection of broiler chickens under field conditions by measurement of humoral and cellular immune responses and screening of challenge and shedding of field H5 carrying AI virus using real time-PCR (RT-PCR) as well as measurement of some parameters concerning mortality and performance. Three chick flocks (one day old) were used in the experimental infection. Two flocks were vaccinated with BEST vaccine while the third was vaccinated with bivalent inactivated H5N1-ND vaccine at 10 days of age. Thirty nine tracheal and cloacal swabs were collected at 35 days of age for RT-PCR as well as 30 blood samples were collected at 10, 25 and 31 days of age for measurement of humoral (HI assay) and cellular immune response (INF- and IL-6 assays). HI titers against of both NDV and AIV-H5 vaccine in the first and second flocks significantly increased reaching the maximum protective level at 21 day post vaccination. In the 3rd flock, HI titers against NDV reached to protective level at 21 day post vaccination while AIV-H5 titers did not. INF- and IL-6 concentrations in BEST vaccinated groups were higher than bivalent inactivated H5N1-ND vaccinated group. Results of RT-PCR of examined samples revealed that 60, 40 and 70 % showed H5 virus blood circulation in the flocks, respectively. It was concluded that BEST vaccine was suggested as an important factor in activation of innate immunity which has been reflected on lowering mortalities, lowering clinical signs of disease and increasing body weight gain.