Document Type: Full paper (Original article)
Department of Poultry Diseases, Razi Vaccine and Serum Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran
Background: Avian Influenza subtype H9N2 is a prevalent viral disease with enormous economic losses in poultry farms through significant respiratory and gastrointestinal manifestations. The degree of protection obtained from a vaccine strongly depends on the level of antigenic similarity between challenge and vaccine virus. Aims: We tried to evaluate possible effects of continuous antigenic changes occurs in circulating Iranian viruses since 1998 on the commercial vaccines, which using vaccine seeds from earlier outbreaks on inhibiting viral replication in target organs of broilers challenged with the recent isolate. Methods: 90 one-day-old broilers randomly grouped into 5 separate groups and vaccinated with autogenous or commercial vaccines. qRT-PCR was done on the trachea and fecal samples of challenged chickens with recent H9N2 to determine viral load. Also, humoral antibodies evaluated by HI. Results: There was no significant difference in H9N2 viral load in the trachea within vaccinated groups on 5 DPC (Days Post Challenge), but on 15 DPC, the autogenous vaccine significantly lowered viral load compared to commercial vaccines (p≤0.05). No significant differences in fecal swab’s viral load observed between autogenous and commercial vaccine A, and both of them significantly inhibited viral load compared to no vaccinated group (p≤0.05). Also, The autogenous vaccine elicits the highest HI (Hemagglutination Inhibition) titer. Conclusion: Inactivated vaccines that use isolates from previous outbreaks, no longer able to create proper immunity against H9N2 and it is time to change vaccine strains to more recently isolates, to have more antigenic similarity with current circulating H9N2 viruses in the region.