Virological study of coinfection of Newcastle disease virus Genotype VII and H9N2 Avian influenza

Abstract

In this study, we investigate the effect of coinfection with avian influenza (subtype H9N2) and velogenic Newcastle disease virus on the pathogenesis and virulence both viruses. In co-infection experiment, one strain of H9N2 by titer 106 EID50 and one strain of VNDV by titer 103 EID50 were used. In experimental design, 70 specific pathogen free chicks (four weeks old) were grouped into 7 groups (G1-G7) ten birds/group. Group 1 was uninfected control group, group 2 and 3 were positive control for H9N2 and VNDV respectively, group 4 infected firstly with VNDV and after 3days it was infected by H9N2 and vice versa in group 5 while in group 6 two studied viruses were inoculated simultaneously. The birds in group 7 were infected firstly by H9N2 and after 14 days were infected with vNDV. The obtained results showed that the mortality due to vNDV infection (G 3) and in group 7 started from 6 Days post infection (DPI) and reached 100% at 9DPI, while the mortalities started at 2 DPI in G4 and at 4DPI in G5,6 also the mortalities were reached 100% at 6,7,8DPI in G4,5and 6. The VNDV shedding in control group (G3); G7; G6 and G4 started at 2DPI by titer 102//bird and it reached to 104/bird at 6DPI. While the VNDV shedding in group5 was reduced by 40% at 2DPI and at 4DPI the all tested birds were considered shedder by titer 5X105/bird. The shedding of H9N2 in group infected with VNDV 3 days prior to H9N2 infection were reduced at 3days post infection (DPI) to 2/5 shedders (40% shedding) compared to 5/5 shedders (100% shedding) in positive control group with significant p value 0.0044 while there was no shedder birds in simultaneous infected group with significant P value ˂ 0.0001. At 5DPI the shedding of H9N2 in group infected with VNDV 3 days prior to H9N2 infection was 100% (3/3 shedder) and was 20% (1/5 shedder) in simultaneous infected group with significant P value 0.046 while it was 40% (2/5 shedder) in positive control group. The shedding reached to 80% (4/5 shedders) in simultaneous infected group at 7DPI. VNDV post infection prolonged and enhanced shedding of H9N2 and reached to 100% at 5DPI compared to 40% in positive control group and completed to 100% at 7DPI while it was 20% in positive control group. . Immunohistochemical results showed that expression of H9 viral antigen recorded the peak in control H9 group in the lung tissue, meanwhile expression of ND viral antigen was maximum recorded in prior infection with H9 in the lung tissue. A significant increase in the H9 expression in the intestine of prior infection with NDV group, however simultaneous infection of both viruses scored the peak of ND expression in the intestinal tissue.