Feline chlamydiosis (aka feline pneumonitis) is a relatively mild, chronic upper respiratory disease caused by the bacterium Chlamydia psittaci. The main symptom is conjunctivitis, an abnormal eye discharge due to inflammation of the conjunctiva, the membrane lining the inside of the eyelid. The infection can also cause nasal discharge, sneezing, and pneumonia. Left untreated, the infection tends to become chronic, lasting weeks or months.

Chlamydiosis is part of the feline upper respiratory infection (URI) complex, a group of viral and bacterial infections (e.g., feline rhinotracheitis, feline calicivirus) that affects the nose and eyes and manifests similar symptoms. Chlamydiosis accounts for about 10% to 15% of all feline URI cases and often occurs with another URI.

Incidence and Prevalence Chlamydiosis occurs worldwide and affects about 5% to 10% of the cat population. It is especially common in kittens (2 to 6 months old), in multicat households, and in pet adoption shelters. Outbreaks tend to occur in overcrowded, poorly ventilated, and unsanitary settings; and where cats are poorly fed or stressed, either physically or psychologically.


Feline pneumonitis is caused by Chlamydia psittaci, an intracellular bacteria (i.e., bacteria that lives inside a cell), which also affects birds and humans. Chlamydia psittaci reproduces in the cells that line the respiratory tract, causing irritation and the mild symptoms that characterize chlamydiosis. It can also reproduce in the gastrointestinal and reproductive tracts but usually doesnít cause symptoms in either place.

Transmission The bacteria that causes chlamydiosis can spread from upper respiratory tract secretions. Common methods of transmission include the following: Contact with contaminated objects, such as cages, food and water bowls, litter pans, pet ownerís clothing, and pet ownerís hands, contact with an infected catís mouth, nose, or eye discharge, sneezing and coughing that propels the virus as far as 4 feet, latent carrier cats that donít show symptoms but harbor the bacteria in their conjunctiva can shed the virus in their eye discharge. The likelihood that bacteria will be present in the discharge is greater after stressful events.

*Though uncommon, there have been reported cases of mild human conjunctivitis caused by feline Chlamydia psittaci.


Chlamydiosis is symptomatic only in the respiratory tract and eyes. The infection may not cause any symptoms, unless another URI is present. When symptoms do appear, the most common include the following: Anorexia (may occur as the disease progresses), coughing, dyspnea (difficulty breathing), fever (may occur as the disease progresses), pneumonia (in young kittens 2 to 4 weeks old, which could be fatal), rhinitis (runny nose), sneezing, watery eyes due to conjunctivitis (either one or both eyes). If kittens do not open their eyes between 10-17 days, then have the kitten checked for Chlamydia.

Although C. psittaci colonizes the reproductive tract, it doesnít cause symptoms. Itís not clear whether it affects pregnancy or not. Sometimes kittens that are born to infected mothers develop severe conjunctivitis at, or shortly after, birth.