Investigation of Immune-based Strategies for Control of Avian Influenza Virus Transmission
Avian influenza viruses (AIV) pose a constant threat for the poultry industry. Infection with H9N2 AIV subtypes has been associated with serious outcomes to poultry health and production, including decreased egg and meat production and morbidity in chickens. The uncontrolled transmission of AIV in poultry species increases the risk of zoonotic outbreaks making it a pathogen of ‘One Health’ concern. Although many nations have adopted biosecurity measures and surveillance programs, predicting future outbreaks requires a thorough understanding of AIV transmission mechanisms. Although transmission is known to occur through direct or indirect contact routes, a detailed information about these transmission routes remains to be explored in chickens. Therefore, the primary focus of the current thesis was to investigate and establish various routes for H9N2 AIV transmission in chickens and analyze the efficacy of Toll-like receptor (TLR) ligands as sole molecules or as vaccine adjuvants to reduce transmission in the above experimentally established transmission models. Our studies revealed that exposure to H9N2 AIV either via aerosol or direct inoculation route can lead to replication of the virus in the gastrointestinal and respiratory tracts. Both inoculation methods effectively established transmission of H9N2 AIV in a ‘direct contact’ model. Further, transmission of H9N2 AIV via the fecal-contact route was investigated. Our results demonstrated that H9N2 AIV in feces from the infected chickens can remain viable in the environment for a specific period of time and infect naive chickens. Subsequently, the efficacy of cytosine-phosphate-guanine-oligodeoxynucleotide (CpG-ODN 2007) and polyriboinosinic polyribocytidylic acid (poly(I:C)) as sole agents was examined in the fecal and direct contact transmission models. Chickens treated (intramuscularly) with CpG ODN 2007 and poly(I:C) led to enhanced innate anti-viral responses and reduced virus shedding and transmission. Additionally, when employed as adjuvants, both ligands exhibited enhanced antibody- and cell-mediated responses with decreased transmission between the infected and recipient chickens. Overall, the key findings of the present research were identifying different modes of H9N2 AIV transmission in chickens by establishing transmission models and employing potential immune-based strategies to control transmission.