Experimental Infection of Broilers with H9n2 Avian Influenza Virus Local Isolate

Abstract

P oultry industry is greatly affected by outbreaks due to avian influenza viruses that spread worldwide. These outbreaks are associated with high morbidity and mortality or high morbidity and low mortality, as it was related to virus strain and subtype (Capua and Alexander, 2008; Goudrazi et al., 2013). Avian influenza viruses are RNA genome viruses, which is single stranded and negative sense RNA. The genome is segmented into 8 segments and their total length of 13.5 kilo base. The virions are enveloped and classified within the family Orthomyxoviridae (Lamb, 2001). All avian influenza viruses are grouped within the genus Influenza A of the family Orthopmyxoviridae, and this family have another four genera which are, Influenza B, Influenza C, Thogotovirus, and Isavirus (MacLachlan and Dubovi 2010). This classification is attributed to the differences in genetic structures of both matrix proteins (MP) and nucleoproteins (NP) of these viruses (MacLachlan and Dubovi 2010). The genus Influenza A included many viruses, these are although related to each other serologically and from genetic point of view, but differences are also detected between research Article Abstract | The present study was an attempt to assess the pathogenicity of local isolate of H9N2 avian influenza virus (AIV) in Diyala province, Iraq in the experimentally infected vaccinated and unvaccinated commercial broiler chickens with available commercial H9N2 vaccine. The virus was propagated in allantoic cavity of hen's embryonated eggs and gave a titer (1024HAU/0.1) by HA test and a (10 10.5 EID50/0.1 ml) of stock virus. One hundred and 80 broilers of one day old were used and subdivided into 3 groups (60 birds each) as group A, B, and C. La-Sota Newcastle disease virus (NDV) vaccine was used to vaccinate groups A, group B was further vaccinated with bivalent inactivated H9N2 and NDV commercial vaccine, whereas group C was used as control (unvaccinated). Groups A and B at the age of 28 days were infected by intranasal dropping with 0.3 ml of stock virus of a titer (10 10.5 EID50/0.1 ml). The mean titre of maternal antibodies measured by enzyme linked immunosorbent assay (ELISA) at 3 days of age appeared as 6541.66. Levels of anti AIV antibodies reduced significantly (P≤0.05) at age of 14 and 35 days when compared to level of maternal antibody. The mean titres of antibodies at 14 days of age appeared 1173.16, 2503.77 and 373.94 for groups A, B and C respectively. The mean titres of IgG against AIV at the age of 35 days appeared as 337.77, 2303.22 and 174.27 for group A, B, and C respectively. Mild clinical signs were observed in A and B groups at 4 and 12 days post infection (PI) respectively. The morbidity was too low and the mortality was reported in group A only and not be exceeded 3.3%. The virus was detected in tissue samples only of group A collected from trachea, liver and lung by real time PCR using specific primers and probe. Histopathological changes were observed in trachea, liver and lung, like degeneration, necrosis and infiltration of i...