Chlamydia psittaci: A zoonotic pathogen causing avian chlamydiosis and psittacosis

Chlamydia psittaci is an obligate intracellular gram-negative bacterium with a unique biphasic developmental cycle. It is a zoonotic pathogen with a wide range of hosts and can cause avian chlamydiosis in birds and psittacosis in humans. The pathogen is transmitted mainly through horizontal transmission between birds. Cross-species transmission sometimes occurs and human-to-human transmission has recently been confirmed. This review provides an updated overview of C. psittaci from the perspective of both avian chlamydiosis and psittacosis. We include the aspects of genotype, host–pathogen interaction, transmission, epidemiology, detection and diagnosis, clinical manifestation, management, and prevention, aiming to provide a basic understanding of C. psittaci and offer fresh insights focused on zoonosis and cross-species transmission.