الفهرس 
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Abstract
Avian influenza (AI) is a highly contagious viral infection affecting food producing birds (chickens, turkeys, quails, guinea fowl, etc.), pet and wild birds. (Irvine et al., 2007). Based on viral pathogenicity IAVs are divided into Highly pathogenic avian influenza viruses (HPAIvs) which spread rapidly and result in high mortality rates (up to 100%) and Low pathogenic avian influenza viruses (LPAIvs) which cause mild infection of bird (OIE, 2011) .
Egypt recorded its first HPAI-H5N1 outbreak in February 2006, which became regularly reported in poultry in almost all of the 29 governorates since that (OIE, 2012). Ducks and wild waterfowl perpetuate all strains of influenza viruses in nature with an asymptomatic infection and little pathology, but the pathogenicity of HPAIA-H5N1 viruses in domestic ducks has increased over time with some viruses producing 100% mortality in very short time. (Swayne et al., 2003). These changes in virulence have been reported with viruses from countries with high population of domestic ducks, including Egypt. Due to the significant role of duck in the maintenance and transmission of HPAI therefore the present study was directed to determine the experimental pathogenesis of HPAIAv in domestic Native ducks using a total number of 60 domestic Native ducks of two weeks- old, seronegative to H5N1which were randomly divided into 3 groups (A, B and C), of 24, 24 and 12 ducks respectively, The groups were classified as group (A) was used to study the pathogenesis.