Experimental study on co-infection of H9N2 avian influenza virus with Ornithobacterium rhinotracheale in specific- pathogen- free chickens

In this study, pathogenesis of co-infection of (A/Chicken/Iran/ m. 1/2010) H9N2 virus and (ORT -R87-7/1387) Ornithobacterium rhinotracheale bacteria, and tissue tropism and dissemination of this co-infection throughout the body of SPF chickens were investigated. The clinical signs and gross lesions of the infected chicks were also monitored. Forty, 21-day-old SPF chicks were divided randomly into two groups (20 chicks in the experimental and 20 chicks in the control group). At the age of three weeks, the chicks in the experimental group were inoculated by eyedrop with the virus of 106 EID50 and intratracheally with the bacteria of 1 ×1010CFU. The samples from various tissues were collected at 2, 4, 6, 8, 10, 12 and 14 days post inoculation (DPI). We used culture on blood agar for detection of the bacteria and isolation assay in embryonated chicken eggs (SPF) to evaluate virus dissemination. Experimental group chickens exhibited depression, reduced appetite, ruffled feathers, more severe respiratory signs and 15% mortality. The most remarkable clinical signs appeared on day 3 PI. H9N2 was detected in the lungs and trachea on days 2 and 4 PI. The virus was also found in the Bursa of fabricius on days 2 and 6 PI. The H9N2 virus was observed only on day 2 PI in Thymus and Liver, and only on day 8 PI in Kidneys. We could not trace the virus in the spleen, cecal tonsils and cloaca during study. ORT was isolated in the swabs of trachea on days 2 and 4 PI. The bacteria was also found in the lungs on day 4 PI. But ORT was not detected in swab samples taken from heart and liver during study. The Results of this study indicated that H9N2 virus and ORT bacteria was not detected from days 6 and 10 PI, respectively and also concurrent infectious with H9 2 virus and ORT bacteria could exacerbates clinical signs and gross lesions in infected chickens