Viral Shedding Evaluation is Critical for Determining Efficacy of Avian Influenza (H9) Vaccines in Broiler Chickens

Viral shedding evaluation is critical for determining the efficacy of avian influenza (H9) vaccines in broiler chickens. This study was undertaken to evaluate the comparative efficacy of commercial and self-prepared AIV H9 vaccines for their potential to stop or reduce viral shedding post challenge infection (PCI) and to develop humoral immunity. A total of 5 groups A, B, C, D and E comprising of 20 broiler birds each were made. Groups A, B and C were vaccinated on 6th day of age with imported (Ivac), local (Lvac) and self-prepared (Spvac) vaccines, respectively. Group D (virus challenged) and E (non-vaccinated/ non-challenged) were kept as control groups. Virus shedding in cloacal swabs, taken on 15 consecutive days PCI from all the groups (25th day, 100 EID50, intranasal) were tested through Real-Time RT-PCR. Humoral immune response were also measured by haemagglutination inhibition (HI) test using blood samples collected at an interval of 5 days till the age of 40 days. In this study, none of the vaccines found effective to prevent virus shedding however statistically, the difference in viral load was non-significant (P<0.5) within the local vaccinated groups while significant (P>0.5) when compared local with imported vaccine and control groups. Post challenge infection, virus shedding started on 3rd day in group D while in all vaccinated groups it was (A: 730, B: 470 and D: 430 copies) on 4th day PCI and was maximum on 6 days PCI (A: 1940, B:1645 and D: 1550 copies) followed by decline. The shedding of virus stopped on 12th day PCI in groups (B and C) while it stopped on 15th day PCI in group A, however in group D, it continued till the end of trial. In present study, antibody titers (geometric mean titer-GMT) showed increasing trends (48.5 to 55.5) in all vaccinated groups (p>0.05) until challenge infection followed by decrease in antibody titer (22.6 to 27.9) for 5 days PCI. This study indicated, all the vaccines found effective in reducing virus shedding and induction of humoral immunity however local vaccines presented robust reduction compared to imported vaccine and can be used preferably due to cost effectiveness and availability to combat avian influenza H9 in poultry birds.