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Beak and feather disease virus and Chlamydiales infections in wild Australian psittacines: no statistical evidence for dependence

ABSTRACT Wildlife can be hosts for pathogens of conservation and zoonotic concern. Infection with one pathogen can increase the risk of co-infection with others, with resulting impacts on hosts, for example on body condition or survival. However, studies of co-infection in wild populations are rare. Globally, psittacine birds can be infected with beak and feather disease virus (BFDV), a circovirus of significant conservation concern, and with bacteria of the order Chlamydiales, including the zoonotic Chlamydia psittaci. These pathogens are common in Australian psittacines, and their putatively immunosuppressive effects would predict co-infection to be more common than expected due to chance alone. Here, we test this hypothesis across four abundant and widespread Australian parrot species: Crimson Rosella, Sulphur-crested Cockatoo, Galah and Blue-winged Parrot. Using wild-caught birds, we tested for pathogen DNA and, in the case of Chlamydiales, also antibodies, to investigate both current and previous infection status. We detected co-infection prevalence of up to 16.4% in the combined samples from the four species and up to 28.9% in Crimson Rosellas, the species with the largest sample size. Contrary to expectations, however, we found that the incidence of infections with the two pathogens was statistically independent. There was also no effect of co-infection on body condition or haematocrit. Our findings therefore suggest that while concurrent infection does occur, it is no more common than expected by chance. We discuss limitations of the data and suggest avenues for future research. Overall, our study provides insights that potentially benefit psittacine conservation, welfare, and human health.