Synergistic effects of infectious bursal disease virus on avian influenza virus h9n2 pathogenicity in broiler chicks

Abstract

In this experiment, pathogenesis of H9N2 avian influenza virus (AIV), experimentally infected with
infectious bursal disease virus (IBDV) in broiler chicks was examined. Three groups of twenty were
randomly selected. Day old chickens in group 1, were infected by 103 CID50 of IBDV intrabursaly, and in
thirty days of age groups 1 and 2 were challenged with 106
EID50 H9N2, intranasaly-intraoculary.
Chickens in group 3 remained as control (uninfected with neither IBDV or AIV). Tracheal and cloacal
swabs, and tissue samples, were collected at 3, 7, and 11 days postinoculation (PI). Serum samples
examined for antibodies against avian influenza virus (AIV) by hemagglutination inhibition test (HI). IBD
caused lower H9N2 antibody level. IBDV infected chickens (g1) shed AI virus for a longer period than
AIV infected birds (g2), from both trachea and cloac. IBDV was related with AIV in brain and liver.
Isolation of AIV from trachea, conjunctiva, bursa and lung in IBDV infected group (1), prolonged till 11
days PI. Our study provides evidence that a previous history of IBDV infection in chickens may cause
them to be more susceptible to H9N2 low pathogenic avian influenza (LPAI) virus infection and may
alter its tissue tropism.