Overview of Feline Chlamydiosis

Feline chlamydiosis (also known as 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 percent of all feline URI cases and often occurs with another URI.

Incidence and Prevalence of Feline Chlamydiosis

Chlamydiosis occurs worldwide and affects about 5 to 10 percent 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 (e.g., extreme temperatures) or psychologically (introduction of a new cat).

Causes of Feline Chlamydiosis

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 doesn't cause symptoms in either place.

Feline Chlamydiosis 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 owner's clothing, and pet owner's hands
  • Contact with an infected cat's mouth, nose, or eye discharge
  • Sneezing and coughing that propels the bacteria as far as 4 feet

Carrier cats that don't show symptoms but harbor the bacteria in their conjunctiva can shed the bacteria in their eye discharge. The likelihood that bacteria will be present in the discharge is greater after stressful events. (e.g., introduction of a new cat into the household).

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

Symptoms of Feline Chlamydiosis

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 (loss of appetite; may occur as the disease progresses)
  • Coughing
  • Difficulty breathing
  • Fever (may occur as the disease progresses)
  • Pneumonia (in young kittens 2 to 4 weeks old, which could be fatal)
  • Runny nose (rhinitis)
  • Sneezing
  • Watery eyes due to conjunctivitis (either one or both eyes)

Conjunctivitis is inflammation of the conjunctiva, the thin, transparent membrane that lines the inside of the eyelid. The inflammation leads to discharge, swelling, and pain; the cat's eyes may be red and weepy. This is the main symptom of chlamydiosis and usually occurs initially in one eye and eventually affects both eyes. Rarely, it becomes chronic.

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

Publication Review By: the Editorial Staff at Healthcommunities.com

Published: 30 Apr 2001

Last Modified: 15 Sep 2015