Studies on Pathogenicity of Local Newcastle Disease Genotype VIIj and Avian Influenza H9N2 Isolates to Commercial Vaccinated Male Layer Chickens

This study was carried out to compare pathogenicity of single and co-infection of Newcastle disease virus (NDV) genotype VIIj and Avian Influenza (AI) H9N2 virus in commercial male layer chicken vaccinated with live ND (Hitchner B1, La Sota) vaccines from different commercial producers in two vaccination schemes. NDV haemaglutination inhibition (HI (log2) mean titers in group received vaccines 1 (4.8 ± 0.8, 2.4 ± 1.2 and 3.9 ± 0.5) were lower than group given vaccine 2 (4.5 ± 1.2, 3.6 ± 1.1 and 4.0 ± 0.4) at 14, 21 and 29 days of age, respectively. Chicken group received ND vaccine 2 and inactivated H9 showed relatively higher HI titres (5.0 ± 1.5, 3.5 ± 1.4 and 4.5 ± 1.3).  HI titres against H9N2 in group given H9N2 inactivated vaccine are 3.7 ± 1.6, 2.5 ± 1.1 and 5.1 ± 1.3 at 14, 21 and 29 days, respectively.   Challenge with Newcastle disease virus (NDV) genotype VIIj at 33 days of age resulted in 100% mortality with severe signs as well as in non-vaccinated control sub-group challenged and 100% mortalities.  Sub-groups (2a, 3a and 4a) vaccinated with ND vaccine 1,  ND vaccine 2 and ND vaccine 2+ H9N2 showed  signs of depression, off food and moderate respiratory signs with protection rates is 70, 70 and 75%,  respectively.  Control group challenged with H9N2 showed general signs with mild respiratory signs and 10% mortalities while, sub-groups given ND vaccine 2+ H9N2 and challenged with H9N2 showed 100% survival. Chicken sub-groups vaccinated with ND vaccine 1,  ND vaccine 2 or ND vaccine 2+ H9N2 and challenged with NDV+ H9N2 (co-infection) showed signs form the  3rd s post infection (dpi) with moderate respiratory signs  and protection rate of 50, 70 and 70%, respectively.  Post-mortem lesions in Velogenic NDV (vNDV) challenged birds were septicemia, intestinal and respiratory lesion, while those challenged with both NDV and H9N2 showed more prominent lesions. The vaccinated groups showed unsatisfactory protection rates (50- 75%). Vaccine 2 showed higher protection and HI titers than vaccine 1. Simultaneous chicken challenge with H9N2 and vNDV pointed out that co-infection increased severity of clinical signs, mortality and gross lesions. Histological changes were reported in lung, intestine, and spleen of challenged non-vaccinated and vaccinated groups. The severity of tissue alteration was remarkably high in the non-vaccinated group and slightly mild tissue alteration in the vaccinated group. The histological changes ranged from severe congestion in blood vessels in tested organ with lymphoid depletion in spleen and hyperplasia of mucosal-associated lymphoid tissue in the intestine, with partial limited tissue change in the challenged vaccinated group. 
The local NDV strain genotype VIIj is highly pathogenic to male layer commercial chickens and the inoculation of NDV with H9N2 at the same time didn›t increase its severity. Also, it was notable that commercial Hitchner B1 and La Sota vaccines conferred partial protection for experimentally used chickens against challenge this ND field isolate.