الفهرس 
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Abstract
Avian influenza (AI) is caused by specified viruses that are members of the family Orthomyxoviridae and placed in the genus influenza virus A. There are three influenza genera – A, B and C; only influenza A viruses are known to infect birds. Diagnosis is by isolation of the virus or by detection and characterization of fragments of its genome. This is because infections in birds can give rise to a wide variety of clinical signs that may vary according to the host, strain of virus, the host’s immune status, presence of any secondary exacerbating organisms and environmental conditions (OIE 2012).
Zoonotic infections by Avian influenza viruses occurred at the human–poultry interface which might case a drastically epidemics if the virus acquires some mutations facilitating human to human transmission.
Control of Avian Influenza outbreaks require first biosecurity measures (encompassing bio-exclusion and bio-containment) and second a good vaccine program. Vaccination has been shown to increase resistance to field challenge, reduce shedding levels in vaccinated birds, and reduce transmission (Capua et al., 2004).
the whole virus inactivated vaccines contain the HA antigen as the main component triggering the immune system, however production of such type of vaccines require a large amount of SPF chicken eggs as early embryonic death occurs due to the high pathogenicity nature of the AI virus . However, owing to their high pathogenicity, handling of the wild-type viruses requires bio-safety level-3 (BSL-3) containment (Kutzler, M.A. and Weiner, D.B. 2008). One of the main points to be mentioned is that the commercially available whole virus inactivated vaccines successfully protect chickens against infection with homologues virus strains, but have a very limited protection against heterologous strains and in some studies clade difference may have a wide variation in the immune response which may result in reemerging outbreaks (Ninomiya et al., 2007).
The vaccination system must allow the detection of field exposure in a vaccinated flock. Conventional inactivated vaccines that contain the same viral subtype as the field virus enable detection of field exposure when unvaccinated sentinels left in the flock were tested regularly. This system was applicable in the field but was rather impracticable, especially for the identification of sentinel birds in premises that contain floor-raised birds. A more encouraging system, based on the detection of anti-NS1 antibodies, has been recently developed and can be used with all inactivated vaccines, provided they have the same haemagglutinin subtype as the field virus (Tumpey et al., 2005) demonstrated. This system was based on the fact that the NS1 protein was synthesized only during active viral replication and, therefore, was rarely present in inactivated vaccines. Another approach to use the inactivated vaccines was the use of heterologous vaccination (the same H but different N subtypes) to maintain the DIVA strategy, yet this vaccination interventions will substantially reduce (although not prevent) secondary outbreaks, depending on the immune status of contact birds and flock.
On the other hand, DNA vaccine expressing single antigen like HA gene will maintain the DIVA strategy by measuring the anti-NA antibodies or Anti-matrix protein antibodies for detection of infection. While those expressing N1 gene will reduce the level of shedding thus reducing environmental load and decreases the secondary epidemics
In the current study, DNA vaccine based on expression of H5 and N1 genes from locally circulating HPAI field isolate will be prepared and tested for its protective efficacy in chickens. Also the level of shedding of the virus after challenge will be examined in regards to the control unvaccinated groups. In order to fulfill such requirements, the following steps will be conducted.