CLINICO-PATHOLOGICAL STUDIES ON CO-INFECTION BETWEEN LOW PATHOGENIC AVIAN INFLUENZA VIRUS H9N2 AND HIGHLY PATHOGENIC AVIAN INFLUENZA VIRUS H5N1

Egypt is a hotspot for both H5 and H9 subtype avian influenza (AI) A virus infections and the continued evolution/circulation of both viruses and their spread across Egypt since 2012 raise the concern that prior H9N2 virus infection may limit the detection of subsequent H5N1 infection in gallinaceous poultry through attenuating the severity of disease. Recent animal
studies have contributed to the growing evidence that temporary non-specific innate immune responses may lead to interference among avian influenza viruses (AIV). In the case of antigenically similar variants of a pathogen such as low pathogenic avian influenza (LPAI) and highly pathogenic avian influenza (HPAI), interference may be similarly manifested at
the host scale through immunological cross-protection(CP);the prevention or partial inhibition of an individual host to future infections may lead to altered transmission dynamics during pathogen co-circulating.In the case of influenza,cross-protection as a consequence of adaptive immunity is expected since neutralising antibodies and cross-reactive cell-mediated immunity are known to act across homo and hetero sub typically diverse viruses.The present results showed that there is cross-protection in the co-infected groups as shown in the decreasing percentage of morbidity and mortality and increasing the percentage of survivability in co-infected groups that challenged with LPAI H5N1 virus and HPAI H5N1 virus at different time intervals than the mono-infected group that challenged with HPAI H5N1 virus. It can be concluded that, the partial cross-protection can lead to change in the  epizootiological pattern of HPAI H5N1 in the field. That is related to circulation of LPAI H9N2, beside the different vaccination strategies used and application of different levels of biosecurity. The current findings can be taken in consideration for the control of HPAI in poultry considering frequent co-circulation of both LPAI and HPAI.