<i>Chlamydia psittaci</i>: A zoonotic pathogen causing avian chlamydiosis and psittacosis

<i>Chlamydia psittaci</i> 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 <i>C. psittaci</i> 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 <i>C. psittaci</i> and offer fresh insights focused on zoonosis and cross-species transmission.