Investigation of Cross Neutralization of Egyptian Variant 2 among both Classic and Variant Vaccinal Infectious Bronchitis Viruses

Abstract

Infectious Bronchitis Virus (IBV) is considered an important virus which may cause major losses in the poultry industry. One of the most important and effective tool that control the infection spread is the vaccination strategy. The present study was undertaken to determine the antigenic relationship between the currently used IBVs, classic and variant vaccinal strains, and the dominating Egyptian variant-2, IBV which could be relatively reflecting the quality of such vaccine. The recommended doses of the monovalent live IBV vaccines of Ma5, H120, 4/91 & CR88, and bivalent vaccine of H120-D274 were administrated via the eye-drop route in groups of 2-week-old SPF-chickens. Three weeks after vaccination, immunized and control chickens were bled, and serum samples were collected. Sera were tested individually for measuring the IBV-Haemagglutination Inhibiting (HI) antibodies against each of IBV-haemagglutinating antigen prepared from the reference classic M41 strain and the Egyptian variant.2 strain (Egy/12/2b spike protein), and IBV- neutralizing antibodies against the Egyptian variant-2 strain. The chicken groups vaccinated with the commercial live vaccines of strains Ma5, H120, 4/91, CR88 and H120-D274 of IBV respectively developed mean serum HI-antibody titers of 6.8, 6.5, 4.9, 5.0 and 5.5 log 2 with the reference classic strain M41-HA antigen, and 3.0, 3.0, 4.4, 4.0, and 4.6 log 2 with the Egyptian variant.2 strain-HA antigen. However, the obtained results revealed utility of VN test more than HI test for assessment of the antigenic relatedness between the vaccinal and challenge strains of IBV as well as testing quality of different commercial live IBV vaccines using the sera of vaccinated chickens against the field strain(s) matched with the homologous strain(s); the antigenic relatedness (r 1 ) between the dominating Egyptian variant-2 strain, and the vaccinal strains, CR88, D274-H120 and H120 of IBV were 33%, 55% and 17% respectively.