Coinfection of avian influenza virus (H9N2 subtype) with infectious bronchitis live vaccine

Abstract

Avian influenza virus of H9N2 subtype is pathotyped as a non-highly pathogenic virus. However, frequent incidences of avian influenza of high mortality that are caused by H9N2 viruses have been observed in broiler chicken farms in Iran and some other Asian countries. Coinfections or environmental factors may be involved in such cases. Infectious microorganisms have been implicating in taking part in the cases of coinfection. We studied the effect of experimental coinfection of H9N2 avian influenza virus with infectious bronchitis live vaccine, which is used extensively in chicken farms in Iran. Clinical signs, gross lesions, viral shedding and mortality rate of the experimentally infected birds were examined. Coinfection of infectious bronchitis live vaccine and H9N2 avian influenza virus led to an extension of the shedding period of H9N2 virus, increasing the severity of clinical signs and mortality rates, causing macroscopic lesions in the embryos.

Fig. 1

a Cast formation in the tracheal bifurcation (arrow) extending to the lower bronchi of a dead chicken from the AIV + IBLV-inoculated group. b Extended tips of cast in the formaldehyde-fixed tracheal sample. These lesions were frequently observed in field cases of H9N2 infection with high mortality

Fig. 2

Twelve-day-old chicken embryos, inoculated with AIV and/or IBLV, showing gross lesions. a Stunting in the embryos inoculated with AIV + IBLV (b1–b4) as compared with an AIV-inoculated embryo (a). b Hyperemia, petechial to ecchymotic hemorrhages in the subcutaneous tissues of an embryo inoculated with AIV + IBLV. It is noteworthy that the embryos inoculated with IBLV or AIV alone did not show any lesions

Fig. 3

Mean HA titers in embryonated chicken eggs inoculated with AIV and AIV + IBLV