الفهرس 
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Abstract
H5N1 HPAIV is now endemic in Egypt and recurrent outbreaks among poultry are likely and the number of human H5N1 infections in Egypt is the highest of any country outside Asia. During the last few years several reports have been published denoting mutation of the Avian influenza virus recently isolated from several poultry flocks and is continuing to mutate with multiple heterogenic strains persisting in Egypt. The relationship between the mutation and pathogenesity has not been clarified. These reports motivated us to perform this study aiming to investigate the morphopatholgical changes of the most recent natural outbreaks of avian influenza in a commercial chicken flocks as well as in the backyard chickens and ducks. In addition to, studying the picture of disease in broiler chicken and ducks experimentally infected with one of these mutant strains (A/ broiler/Egypt /3982-3/2010 H5N1), recently isolated from broilers chickens.
The present study was performed on a total number of 30 dead and diseased broiler chicken, were collected from six diseased flocks, 5 case each, in addition to25 samples collected from 5 backyards flocks from different villages in Damanhour governorate. And 10 dead and diseased ducks were also collected from5 diseased backyards flocks that were reared with the same infected chickens flocks from different villages in Damanhour governorate. The samples were collected during January2009 till April 2011, during the outbreaks of highly pathogenic avian influenza virusinfectionH5N1in Egypt.
In addition to, twenty nonvaccinated, 4-week-old, broiler chickens, chickens were experimented, (fifteen were experimentally infected and five chickens left as acontrol group) and addition to, fifteen 60 days old, nonvaccinated, pekin ducks(ten were experimentally infected and five left as acontrol group). Subsequently the experimental group of chickens and five of ducks were inoculated intranasally with 106 EID50 per bird of H5N1 avian influenza virus at 30, 60 days old age, for chicken and ducks respectively. The other five ducks received the double dose of the dose given to the chicken. Five chickens from the inoculated group were sacrificed 24 hrs after appearance of clinical signs while the rest were lift until succumbed. The clinical signs and gross lesions were recorded.
Tissue specimens of liver, lung, kidney, spleen, trachea, pancreas and brain, were collected for virus isolation and histopathological examination.
Most of the naturally infected chicken progressively developed clinical signs represented by severe cyanosis of the comb and wattles with hemorrhage at the shanks, depression, ruffling feathers and loss of appetite with high daily mortalities. However, chickens experimentally infected showed signs begun with depression, ruffling feathers and loss of appetite, then cyanosis of the comb and wattles, with hemorrhage at the shanks, in most of them. All infected chickens die with in 48hrs, from appearance of clinical signs. The ducks naturally infected showed severe neurological signs before death. However, ducks experimentally received the same dose of the chickens, did not show any signs of illness, in contrast to the ducks, received the double dose, that ducks showed severe neurological signs such as torticollus, seizures, twisting of head and inability to stand at day 14th post inoculation and finally death occur but within three days from appearance of clinical signs.
Grossly, most of the cases showed hemorrhages and congestion in most of the organs particularly lung, liver, spleen, trachea and kidney. All natural cases were proven positive to (H5N1) by immunochromatography and isolation and identification by RT-PCR, HA, and HI tests (using monospecific H5N1 antisera).
The histopathological examination for both naturally and experimentally infected chickens revealed presence of severe congestion and hemorrhages, in most of the organs showed gross lesions, particularly lung, liver and kidney. Microscopic erosive tracheitis, interstitial pneumonia and severe congestion and perivascular oedema were constant. Hepatocyts necrosis and infiltration of mononuclear cells and heterophils were common. The Kidney showed renal tubular necrosis and diffuse congestion. The brain showed, multifocal, moderate to severe necrosis of neurons and glial cells and hemorrhages were found in the cerebrum. Prominent multifocal glial nodules and occasional neuronophagia could be observed in the cerebral gray and white matter. Multifocal perivascular cuffing with lymphocytes and fewer histiocytes were also observed. The other organs showed moderate changes. Histopathological lesions were the same in both natural and experimental birds but they differ in the degree of the severity as lung, pancreas and brain lesions are severe in experimental infection than natural in the chickens while kidney, liver and spleen were severe in natural infections. Other organs lesions were the same in natural and experimental infections. In ducks, the lesions were similar.
We could finally conclude that, Occurrence of the disease in farmed vaccinated chickens indicate without dought failure of vaccinations strategy, or failing of vaccination procedure adopted by agriculture authorities, and both should be reconsidered as have been previously reported. Based upon the results of the present investigation, we could conclude that, the pathological and immunohistochemical changes observed in this study were similar to those described in similar and other bird species infected with HPAI virus. In addition; Absence of fibrinopurulent inflammation of the upper respiratory tract, sinuses, air sacs or reproductive organs that are typical for infections by avian influenza strains of low pathogenicity, indicate that AI virus strains now circulating among birds in Egypt are highly pathogenic and the results of experimental work in the present investigation tell us that, the mutations that do occurred to the virus in the last years did not reduced it’s virulence, pathogenecity or the pathological picture of the virus in the affected bird species.