Pathogenic interactions between Chlamydophila psittaci and avian pneumovirus infections in turkeys.

Both Chlamydophila psittaci and avian pneumovirus (APV) are highly prevalent in Belgian turkeys and might contribute to the respiratory disease complex observed in turkeys. Initial outbreaks of chlamydiosis occur mostly at the age of 4-8 weeks, often accompanied by an APV infection in APV non-vaccinated farms. Regardless APV vaccination, breakthroughs of APV infection from 8 weeks on do occur, a period when also a second C. psittaci infection appears. Therefore, this study examined the pathogenicity of an APV superinfection in C. psittaci predisposed turkeys. Turkeys were infected with C. psittaci, APV or with C. psittaci followed by APV. Simulating the impact of an APV infection during the acute phase or latent phase of a C. psittaci infection, turkeys have been infected with APV at 1 and 5 weeks post C. psittaci infection, respectively. APV infection during the acute phase of a C. psittaci infection aggravates the severity of clinical signs, macroscopic lesions, pharyngeal APV excretion and histological tracheae lesions. In contrast, no clear interaction could be established after APV infection in latently C. psittaci infected specific pathogen-free (SPF) turkeys. This study clearly demonstrates the exacerbating role of APV during acute C. psittaci infection, which can play an important role in the respiratory disease complex of turkeys.