Feline Chlamydiosis (Chlamydia)

What is feline chlamydiosis?
Feline chlamydiosis or chlamydia is an infection caused by a bacterium-like organism. It is an unusual bacterium because it lives and multiplies inside the body cells of the cat whereas most bacteria live outside cells. The full name of the bacterium is Chlamydia psittaci (feline strain). In the past this condition was also known as Feline Pneumonitis. Pneumonitis implies inflammation of the lungs but most problems associated with Chlamydia infection in cats involve inflammation of the upper respiratory tract particularly conjunctivitis that is often recurrent or chronic.

How does a cat become infected with Chlamydia?

Because Chlamydia lives inside cells of the body and is not able to survive for long in the environment, spread of infection relies on direct or close contact with an infected cat.

Following infection, the incubation period or the time before development of disease associated with infection is between three and ten days.

Which cats are most at risk to this disease?
Young cats and kittens are especially vulnerable to this infection although Chlamydia can be detected in cats of all ages. It is one of the most common causes of infectious conjunctivitis in cats.

What clinical signs does a cat infected with Chlamydia develop?
The bacterium primarily infects the conjunctiva which are the delicate membrane lining the eyelids and covering the edges of the eyeballs causing inflammation known as conjunctivitis. In normal cats the conjunctiva is not readily visible and has a pale, salmon pink color.In cats with conjunctivitis, the conjunctiva becomes swollen and reddened often making it more visible. The nictitating membrane or “third eyelid” in the inner corner of the eye may protrude partially across the eye and become red. One or both eyes may be involved. Affected cats initially develop a watery discharge from the eyes that quickly becomes thicker and is usually a yellow or greenish color. The eyes are uncomfortable and cats often keep the affected eye(s) closed. Most cats remain bright and otherwise appear normal, but some may develop a fever or lose their appetite. After one or two days, sniffles and sneezing may also occur. In adult cats, infertility can result from infection. In kittens the infection may be widespread and cause a fatal pneumonia.

If left untreated, the conjunctivitis and associated discomfort and discharge may persist for several weeks or months during which time the cat is also a source of infection to other cats. There may be apparent recovery and then relapse.

How can Chlamydia be diagnosed?
Chlamydia infection can be diagnosed in several ways, with isolation of the organism being the method of choice. This involves taking a swab sample from the conjunctival membrane. The swab is then placed in special transport media and sent to a laboratory where the organism can be grown in culture and identified. Sometimes the Chlamydia organisms may be seen in stained smears. Another option is a blood test for the presence of Chlamydia antibodies. This test can be useful in cases where a negative laboratory culture result is received or as a general screening test of catteries or multi-cat households where conjunctivitis is a chronic problem. Chlamydiosis can be difficult to diagnose because there are many causes of conjunctivitis and cats may have multiple infections at the same time.

Are other cats in the household at risk of infection?
Chlamydia is spread by close or direct contact with an infected cat so any other cats in the home may have come into contact with the bacterium and be infected. For this reason, once Chlamydia has been diagnosed, all cats in the household should be treated.

Is my family at risk?
Occasionally cases of Chlamydia conjunctivitis occur in people in the same household as affected cats. If anyone is having sore or runny eyes they should consult their doctor and tell him or her that there is Chlamydia infection in the cat. Such infection is uncommon and once diagnosed is readily treatable.

Is there any treatment for Chlamydia?
Chlamydia is a bacterial infection, and it can be successfully treated with a course of oral antibiotics. Only certain antibiotics are able to penetrate inside the cells where Chlamydia resides. Treatment must be continued for a minimum of four weeks and for at least ten days after the eyes appear normal. In some cases, topical antibiotic treatment in the form of eye ointment may also be given.

Since some cats can be infected sub-clinically (not show signs themselves but act as a source of infection to other cats) treatment should be given to all of the cats in the household.

Although the infection can be debilitating in some cats, it is treatable with a low risk of recurrence as long as the entire household is thoroughly treated.

How can chlamydia be prevented?
Various vaccines are available and are most useful in breeding catteries where it can be difficult to completely eliminate Chlamydia. In colonies where Chlamydia is endemic, vaccinations are recommended to minimize the risk of future outbreaks.

Vaccination may also be desirable in Chlamydia-free colonies and in household pets to provide protection for high risk situations such as boarding catteries and breeding. Chlamydia is often a component of multivalent (multiple organism) vaccines for cats. Your veterinarian will advise you on the appropriate vaccination choices for your cat.