Chlamydiosis, (parrot fever, psittacosis), is an infection caused by bacteria of the genus Chlamydia. Severity of the disease differs by bacterial strain and the susceptibility of different bird species. Infection occurs from inhaling bacteria in airborne particles of feces or respiratory exudes. Bacteria in the environment can remain infective for several months. Parrots, parakeets, macaws, cockatiels, and other caged birds are most commonly identified with this disease. Waterfowl, herons, doves, and pigeons are the most commonly infected wild birds in North America. The feral city pigeon (rock dove) is the most common carrier of Chlamydia spp. in the United States. Chlamydiosis can be a serious human health problem. Persons working in an area with airborne avian fecal material should wear a mask or respirator, and should avoid working with birds in areas with low ventilation.

Field signs

Signs of chlamydiosis depend on the bird species and bacterial strain. Infection can be acute, chronic, or unapparent. Signs include lethargy, fluid discharge with pus from the eyes and nares, loss of appetite, diarrhea, and huddled position with ruffled feathers. Feral pigeons exhibit many of these signs, and mortality rates in young pigeons are very high.