Avian influenza H9N2 is one of the most commonly circulating viruses in numerous Egyptian
poultry farms. The Asian lineage H9N2 exhibits an immunosuppressive effect, and its
pathogenicity is amplified when it co-infects with other pathogens, especially with the
immunosuppressive infectious bursal disease virus (IBDV), resulting in increased mortality
rates. Both vaccines and field infection can exacerbate the pathogenicity of H9N2,
particularly in the bursa of Fabricius, causing more significant lymphoid depletion. To
comprehend the impact of the IBD vaccine on the viral and pathogenic effect of H9N2
infection in specific pathogen-free chicks (SPF), the experiment was designed as four
groups; group 1 served as the negative control, group 2 received (228E) IBD vaccine, group
3 was challenged with H9N2, and group-4 was vaccinated by the IBD vaccine then
challenged with H9N2. The clinical signs, relative immune organs weights and
histopathological lesion scores were recorded. The tracheal and cloacal H9N2 viral shedding
were also measured. Group 4 exhibited a significant decrease (P ≤ 0.05) in the relative bursal
weight and an increase in the bursal lesion score when compared with groups 1 and 3 at 4
and 8 days post-challenge (dpc). The tracheal lesion score of group-4 recorded a significant
increase when compared with groups 1 and 3. The renal lesion score of group 4 achieved a
significant increase when compared with 1 and 3 at 8 dpc. Also, group 4 recorded a
significant increase in H9N2 shedding in comparison with groups 1 and 3. Consequently,
our study concluded that routine vaccination with the IBD intermediate plus vaccine
exacerbates the silent infection of H9N2 resulting in outbreaks. |
