Epidemiological study on the impact of vaccination programs on antigenic relatedness, genetic characterization of highly pathogenic avian influenza H5N1

Two HPAI H5N1 viruses were isolated from vaccinated layer and broiler commercial poultry farms in Egypt at years 2011 and 2013; respectively. By phylogenetic analysis, the viruses fall into two genetically diverse clades: [i] A/chicken/Egypt/VRLCU67/2011 classified as a variant virus, clade 2.2.1.1; and [ii] A/chicken/Egypt/13VIR3729-4/2013 classified as a classic virus, clade 2.2.1. Cross HI-test confirmed that the reaction between the two viruses is weak; furthermore, it showed the antigenic diversity between viruses belong to different clades and antigenic groups. Antigenic relatedness was calculated between six AI antigens and their antisera representing the different clades and antigenic groups circulated in Egyptian field; including the A/chicken/Egypt/VRLCU67/2011 strain which showed very low R-values with the other viruses' groups; ranging from 17 % to zero. Results demonstrated the genetic and antigenic diversity of the variant viruses and how can the vaccine seed be a weak point in the vaccination program that could be broken by the drifted viruses antigenically distant from the vaccine strain

Effect of infectious bursal disease field vaccines on avian influenza vaccination immunity

Traditional live Infectious Bursal Disease virus [1DDV] vaccines were thought to have some v-4 degree of adverse effect on the bursa of fabricous of chickens, which in turn may interfere with antibody production against other poultry vaccines. In this study, 15 broiler flocks vaccinated -; against avian influenza [AI] virus were sampled for serum. The flocks have received IBDV vaccination either from the conventional live vaccines or with the new recombinant subunit vaccine. Haemagglutination inhibition [HI] test was carried on sera using different AI antigens. Sera measured by the variant A/chicken/EgypWRLCU67/2011 [H5N1] isolate showed significant difference [P<0.05] between mean HI titers of bird vaccinated by traditional IBDV. vaccines and titers of those vaccinated with the subunit vaccine. Results indicate that live IBDV vaccines may affect the efficacy of AI vaccine, and the study encourages the use of the field AI isolates for reliable interpretation of HI test results