الفهرس 
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Abstract
In this study, we evaluated different factors affecting sero-surveillance against avian influenza in chickens. from November 2010 till December 2013; a total of 382 blood samples for serum and 262 eggs were collected from different chicken commercial farms for haeagglutination inhibition (HI) testing. In case of suspicion of influenza infection; tracheal and cloacal swaps and organ samples were collected for virus isolation and identification. The variant A/chicken/Egypt/VRLCU67/2011(H5N1) and the classic A/chicken/Egypt/13VIR3729-4/2013(H5N1) viruses were isolated from a layer and a broiler farms; respectively. Cross-HI and antigenic relatedness testing revealed that the variant strain is distantly related to other tested Egyptian viruses with R% less than 50%. HI testing of sera and egg yolk using the commercial H5N2 Mexican antigen and the isolated viruses revealed the significant difference between results obtained by H5N2 or the classic isolate compared to the variant one. Egg yolk testing for antibodies compared to serum showed high correlation (r=0.79 - 0.98), putting in mind the type of HI antigen used. Using LPAI H5N2 as HI antigens may lead to miss interpretation of HI results, as it showed antigenic diversity to the variant isolate. Birds vaccinated with conventional live Infectious Bursal Disease (IBD) vaccines showed HI titers against AI vaccination lower than those birds vaccinated with IBD sub-unit vaccine; due to the possible effect of live IBD vaccines on the bursa of fabricous, and hence, IBD sub-unit vaccine is more preferred.