Psittacosis, also known as parrot fever and ornithosis, is a zoonotic infectious disease in humans caused by a bacterium and spread by infected parrots such as macaws, cockatiels, and budgerigars, as well as pigeons, sparrows, ducks, hens, gulls, and many other bird species. Canaries and finches are thought to have a lower infection rate than psittacine birds. Infection in birds is known as avian chlamydiosis. Infected birds excrete the bacteria in their faeces and nasal discharges, which can remain infectious for months. Many strains remain dormant in birds until they are activated by stress. Birds are excellent, highly mobile vectors for the spread of chlamydial infection because they feed on and have access to the detritus of all types of infected animals. In birds, infections are frequently systemic, and they can be subtle, severe, acute, or chronic, with intermittent shedding. In birds, symptoms include red eyes, difficulty breathing, watery droppings, and green urates. Strains infect respiratory mucosal epithelial cells and macrophages in birds. Septicaemia eventually develops, and the bacteria are found in the epithelial cells and macrophages of almost all organs, as well as the conjunctiva and gastrointestinal tract. It can also be passed on through the eggs. Stress frequently causes the onset of severe symptoms, which can lead to rapid deterioration and death.