Experimental infection of broilers with H9n2 avian influenza virus local isolate

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 (1010.5EID50/0.1 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 (1010.5EID50/0.1 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 inflammatory cells. In conclusion, available commercial inactivated H9N2 vaccine, could not completely protect broilers from the infection of same virus H9N2 local isolate.