A study of Experimental Infection with Ornithobacterium Rhinotracheale on Pathogenesis of Avian Influenza Virus H9N2 Subtype

The purpose of this study was to investigate effect of secondary infection with Ornithobacterium rhinotracheale (ORT) on pathogenesis of avain influenza virus subtype H9N2 in specific pathogen-free (SPF) chickens. Sixty, one-day-old SPF chicks were randomly divided into three groups. They were kept in separate positive pressure isolators. On 21st day of study, the chicks in group 1 was infected intraocularly with 1×106 EID50 of H9N2 and three days later intratracheally with 1× 1010 CFU of ORT, group 2 only inoculated with H9N2 AI virus, intraocularly. Control group was inoculated with PBS, intraocularly. The samples from various tissues were collected at 6, 8, 10, 12, 14 and 16 days post-inoculation (DPI). In first group chickens exhibited ruffled feathers, depression, respiratory signs, reduced appetite and 10% mortality. The most remarkable clinical signs appeared on day 5 PI. While in second group had minor clinical signs. The H9N2 virus was not detected from organs of group 1 with increasing antibody except lungs of died bird on days 5 PI. The ORT was detected in the trachea and lungs on days 6 and 8 PI. The bacteria was also found in the heart and liver on day 8 PI and in trachea of died birds on days 5 and 7 PI. The results showed that infected chickens with the H9N2 AI virus under secondary infection by ORT cause exacerbate virulence and lesions of H92.