Psittacosis, known also as chlamydiosis or parrot fever, is a disease seen in birds, humans and other animals, and is caused by the bacteria Chlamydia psittaci. In psittacines, psittacosis can cause symptoms ranging from an apparently healthy bird with no problems, to a bird with respiratory signs (sneezing, runny eyes, conjunctivitis, difficulty breathing), poor feathering, weight loss, lethargy, or lime-green diarrhea.

The organism that causes chlamydiosis is highly contagious, and is shed in the droppings and in respiratory fluids (through sneezing, discharge from the eyes, etc.). Because of this, the birds most at risk for chlamydiosis are those in pet stores, aviaries, quarantine stations, or anywhere where there are multiple animals, particularly when there are frequent new additions. Any new introduction to a household should be quarantined away from other birds for at least 45 days, during which time they should be tested for chlamydia. Macaws, cockatiels and amazons seem to be particularly susceptible. Young birds and birds that are stressed (by moving to a new home, ill, on a poor diet) also seem to be prime targets for infection.

Infection with chlamydia can be acute or chronic. In acute cases, the affected bird becomes suddenly ill shortly after being infected. These are the "typical" cases of psittacosis, with the classic signs (lime green droppings, anorexia, possibly red and irritated eyes).

Chronic cases are more difficult to recognize. These birds were infected long ago (weeks, months, even years) but never presented with severe signs. They are usually birds that are not "quite right," with dull or shabby feathers, poor appetite, or frequently sleeping. Chlamydia can also exist in a carrier state, in which the affected bird acts and looks normal, but can shed the bacteria and infect other birds in the household or aviary. This is particularly true with cockatiels, who have a notorious reputation as being carriers of psittacosis, many of which appear healthy or only mildly ill.

Diagnosis of a bird suspected of having chlamydiosis can be difficult. Any ill bird should have a blood profile with a white blood cell count performed. A high white blood cell count and an elevation in liver enzymes indicating liver damage can signal infection with chlamydia. There are also several other blood tests available that test specifically for the presence of the chlamydia organism, or that detect the antibodies to the bacteria, indicating exposure. A positive test is usually definitive, and indicates current infection or recent exposure, however, a negative test does not always mean the bird is free of the disease, and other tests should be run in addition to assure the health of the bird. The physical condition of the bird should also play a role in the diagnosis of the disease. A negative psittacosis test in an ill bird who was recently purchased from a pet store, and who has an elevation in liver enzymes and a high white count, is still considered a potential candidate for chlamydia, and should either be treated or tested further. X-rays can also suggest chlamydiosis, as infected birds will often have an enlarged liver or spleen.

Treatment is fairly straightforward and can be very successful. Chlamydia is susceptible to tetracycline-derivative antibiotics. Treatment of individual birds is done by twice daily dosing with liquid antibiotic, or by injections every ten days. In flocks where birds cannot be handled, or where there are too many birds to treat individually, medicated food or water can be given. Regardless of the way a bird is medicated, treatment should continue for at least 45 days, due to the long life-cycle of the chlamydia organism. In addition, because of the highly contagious nature of this bacteria, all birds in the household or aviary should be treated, not just the ill ones.

The important thing to remember about psittacosis is that it is the great masquerader. Affected birds do not always look sick. Test and quarantine ALL new birds regardless of where they are from, even if they appear to be healthy. It is not worth saving a few dollars if it means risking your other birds' or your own health.