Comparison of the efficacy of four antimicrobial treatment schemes against experimental Ornithobacterium rhinotracheale infection in turkey poults pre-infected with avian pneumovirus

The clinical efficacy of drinking-water administration of enrofloxacin for 3 and 5 days, amoxicillin for 5 days and florfenicol for 5 days for the treatment of respiratory disease induced by an experimental Ornithobacterium rhinotracheale infection in turkeys pre-infected with avian pneumovirus (APV) was assessed based on clinical, bacteriological and histopathological examinations. Experimental groups of 15 susceptible 3-week-old turkeys were each inoculated oculonasally with APV subtype A and 3 days later with susceptible O. rhinotracheale bacteria. Antimicrobial treatment started 1 day after O. rhinotracheale inoculation. After infection, the birds were examined and scored for clinical signs, swabbed daily and weighed at different times. Five birds were euthanized and examined for macroscopic lesions at necropsy at 5 days post bacterial inoculation, and the remainder at 15 days post bacterial inoculation. Samples of the turbinates, trachea, lungs, air sacs, heart and pericardium were collected for bacteriological and/or histological examination. Recovery from respiratory disease caused by an APV/O. rhinotracheale dual infection was most successful after enrofloxacin treatment, irrespective of treatment duration, followed by florfenicol. Amoxicillin treatment was not efficacious. Clinical signs and the number of O. rhinotracheale organisms re-isolated from the trachea and the different respiratory organs were significantly reduced by enrofloxacin treatment for 3 and 5 days. O. rhinotracheale bacteria were not re-isolated from the tracheas of the birds treated with enrofloxacin except for one bird in the 5-day group, as early as 1 day after medication onset. In the group treated with enrofloxacin for 5 days, O. rhinotracheale organisms with a higher minimal inhibitory concentration value (x8) were isolated starting 2 days following treatment onset, initially from a single turkey and subsequently from the other animals.