Pathobiology, Molecular Characterization and Control of Avian Influenza Viruses

Abstract

Respiratory tract infections are major causes of infections in poultry in this country. A number of pathogens are incriminated in causing such infections, most of which are successfully controlled by using effective vaccines. The major organisms causing severe respiratory tract infections in poultry include avain influenza virus (AIV), infectious bronchitis virus (IBV), Newcastle disease virus (NDV), Escherichia coil (E.coli) and Ornithobacterium rhinotracheale (ORT). The present study was conducted to particulary evaluate the role of avian influenza virus in causing severe respiratory tract infection in chickens. By undertaking serological evaluation of the blood samples collected from different parts of the country using HI and ELISA, it was found that AIVs were present among broliers, breeders and layer flocks throughout the country. With the help of various antibody determination and virus isolation techniques, AIV serotypes H9N2 and H7N3 were specifically detected from the field outbreaks. The isolated viruses were further characterized on the basis of their biological and molecular characteristics. A polymerase chain reaction (PCR) based diagnostics assay was also established for the setection of AIV from the field specimens. To further evaluate the pathogenicity of new isolate of H9N2 serotype alone or in association with other pathogens, it was inoculated in experimental birds via different routes. The birds were later on separately challenged with IBV, ORT, or E.coil. The virus isolation and seromonitoring data of these experiments revealed a significant role of E.coil in aggravating the conditions of the birds earlier infected with AIV. In another experiment it was found that in chemically immunosuppressed birds AIV infection by H9N2 produced high molarity with overt respiratory signs. The overall results of this study revealed that more than one serotype of AIV existed in poultry flocks throughout the country which are causing the respiratory tract infection of previously unknown etiology alone and/or in association with secondary infection by other bacterial as well as viral pathogens.