Psittacosis is caused by an infection with the bacterium *Chlamydia psittaci*, which primarily lives in birds. This bacterium can remain dormant in birds but becomes active when the birds experience stress, such as during capture, confinement, or transportation. When active, *C. psittaci* can be shed in bird secretions, droppings, and feather dust, contaminating the environment around the birds.
Humans typically contract psittacosis by inhaling tiny particles from dried bird droppings, secretions, or dust contaminated with the bacteria. This airborne transmission is the most common route, especially in places where birds are kept in close quarters, such as pet shops, aviaries, poultry farms, or during the handling and transport of birds. Direct contact, such as mouth-to-beak contact with infected birds, can also transmit the bacteria, but inhalation of contaminated particles is the primary mode of infection.
The disease is often linked to parrots and other psittacine birds, but *C. psittaci* can infect a wide variety of bird species, including pigeons, ducks, turkeys, and chickens. Birds may carry the bacteria without showing symptoms, making it difficult to detect the infection in avian populations. Stressful conditions for birds, like overcrowding or poor ventilation, can increase bacterial shedding and the risk of transmission to humans.
Once inhaled, *C. psittaci* infects the respiratory tract of humans, leading to symptoms that often start like the flu but can progress to a serious lung infection known as psittacosis or parrot fever. The bacteria are intracellular, meaning they live inside the cells of the host, which can make the infection harder to detect and treat.
Historically, psittacosis gained attention during the 1929–1930 pandemic, when the disease spread globally through the trade and transport of infected parrots and other birds. This event highlighted how the stress of capture and confinement activates the bacteria in birds, increasing the risk of human infection.
People at higher risk include those who work closely with birds, such as pet shop employees, poultry workers, veterinarians, and zookeepers. Preventive measures include wearing masks or respirators to avoid inhaling contaminated dust and maintaining good hygiene and ventilation in bird-handling environments.
In summary, psittacosis is caused by the bacterium *Chlamydia psittaci*, which is transmitted to humans mainly through inhaling contaminated bird droppings, secretions, or dust. The bacteria live in birds, often without causing symptoms, but become infectious when birds are stressed, leading to potential outbreaks in humans exposed to these birds or their environments.
