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% 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 (e.g., extreme temperatures) or psychologically (introduction of a new cat).
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.
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.
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)
* 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)
* 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.
Diagnosis is usually based on clinical symptoms, as well as the cat's medical history. Several tests can detect C. psittaci in the cat's eye discharge and confirm the diagnosis. They involve using cotton or gauze to collect eye discharge samples from the conjunctiva.
Swab samples can be stained with a special dye that identifies inclusion bodies (structures inside the nucleus of bacteria-infected cells). Inclusion bodies are more numerous during the first 4 to 7 days of clinical disease.
A bacterial culture (the growth of cells in a special medium so the bacteria can be identified) can be done, though it can be difficult to distinguish C. psittaci from normal respiratory tract bacteria.
Immunofluorescent assay (IFA) uses special proteins labeled with a fluorescent chemical to locate C. psittaci antibodies (proteins that the immune system manufactures to fight the bacteria). If the antibodies are present, the bacteria are present.
Clinical symptoms of chlamydiosis are similar to those of other feline upper respiratory infections.
Cats with feline calicivirus infection usually have ulcerative stomatitis (an inflammation of the mouth that causes ulcers on the tongue and lips) and are more likely to have pneumonia. Because it's caused by a virus and not a bacteria, calicivirus infection does not respond to antibiotics.
Cats with rhinotracheitis usually have severe sneezing (as opposed to occasional sneezing), more rapid onset of conjunctivitis, and ulcerative keratitis. Rhinotracheitis is also caused by a virus, so it doesn't respond to antibiotics.
Some cats with URI symptoms may have pneumonia caused by another type of bacteria, which should be identifiable on a lung x-ray.
Chlamydiosis usually is mild enough to be treated with antibiotics on an outpatient basis. Tetracyline eye ointment is usually prescribed to treat the infection. Cats generally need to be treated for several weeks, sometimes as long as 6 weeks. In cases of chlamydiosis outbreaks in multicat households or pet adoption shelters, all the cats may need to be treated. Pet owners should keep their cat's eyes and nostrils clean and clear of discharge.
Infected cats should be separated from other cats and kept indoors to prevent the spread of infection, and to minimize the cat's exposure to outdoor stressors, like fights with other cats.
Some veterinarians recommend that infected cats be vaccinated. Vaccination can reduce the severity and duration of the disease. Some cats may experience a slight adverse reaction to the vaccine (i.e., a short-lived, mild, clinical disease).
Supportive nutritional therapy (e.g., feeding the cat through a tube or intravenously) generally isn't necessary unless the infection occurs with another URI, and the cat becomes anorexic.
Cats that live in multicat households or pet adoption shelters should be vaccinated. Vaccination may not prevent infection, but it can reduce the severity and duration of disease. Cats should receive one vaccination at their initial visit, and annual vaccinations thereafter.
Veterinarians generally recommend that cats that live in single-cat households not be vaccinated because the incidence of disease is so low.
Chlamydiosis is a mild disease, and the prognosis is generally very good. It tends to be chronic unless the cat is treated with tetracycline.