الفهرس 
Studies On New Field Strains Of Avian Influenza In Chickens
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Abstract
Low pathogenic avian influenza (LPAI) H9N2, highly pathogenic avian influenza
(HPAI) H5N1, and H5N8 circulate in Egyptian poultry and cause veterinary and
public health significance. The co-circulation of such zoonotic viruses among poultry
in Egypt for several years should render that country a hypothetical hotspot for the
emergence of new reassortants, or may limit the detection of subsequent HPAIV
infection in gallinaceous poultry by 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 LPAI-H9N2 and
HPAI-H5N1, interference may similarly manifest 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 cellmediated immunity are known to act across homo and hetero sub typically diverse
viruses. The main objective of this study was designed to mimic the consequences of
natural co-circulation of LPAI H9N2 and HPAI H5N1 viruses without the effect of
different vaccination strategies used and circulation of other pathogens. The disease
consequence of HPAI H5N1 in chickens that pre-infected by LPAI H9N2 in different
time intervals were monitored and evaluated by collection of cloacal and tracheal
swabs for studying virus shedding by RT-PCR test, blood samples to evaluate post
challenge immune response using ELISA and HI, and organs collected for
histopathological examination to study tissue tropism. Our results showed that there is
cross-protection in the co-infected groups as shown in the decreasing percentage of
morbidity, 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 change in the epizootiological pattern of HPAI H5N1 in the
field 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.