Experimental study on tissue tropism and dissemination of H9N2 avian influenza virus and Ornithobacterium rhinotracheale coinfection in SPF chickens.

Forty-two, one-day-old specific pathogen-free (SPF) chickens were randomly divided into two groups. On 21 st day of study, experimental group was infected intraocularly with 1×10 6 EID50 of H9N2 and intratracheally with 1× 10 10 CFU of Ornithobacterium rhinotracheale (ORT). Control group was inoculated with sterile PBS intraocularly. The samples from various tissues were collected on days 2, 4, 6, 8, 10, 12, 14 and 16 post-inoculation (PI). Experimental group chickens exhibited more severe respiratory signs, depression , anorexia and 15% mortality. The ORT was isolated in the trachea from days 2–4 PI and in the lungs on day 4 PI. The H 9N2 virus was detected in the lungs and trachea from days 2 –4 PI. The virus was also detected in the bursa of fabricius on days 2 and 6 PI and in thymus and liver on day 2 PI. The virus was found only on day 8 PI in kidneys. The virus detection from organs was reduced with increasing antibody titer on day 8 PI. The results of this study indicates that concurrent infection with H 9N2 virus and ORT can exacerbate virulence and lesions of H9N2.