What is feline chlamydiosis?

Feline chlamydiosis is caused by a bacterium-like organism. It is an unusual bacterium because it lives inside the cells of the body whereas most bacteria live outside cells. The full name of the bacterium is Chlamydia psittaci (feline strain); in the past it was also known as feline pneumonitis.

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 (time before development of disease associated with infection) is between 3 and 10 days.

Which cats are most at risk of this disease?

Young cats are especially vulnerable to this infection although Chlamydia can be detected in cats of all ages and is the most common cause of conjunctivitis in cats.

What clinical signs does a cat infected with Chlamydia develop?

The bacterium primarily infects the conjunctiva (the delicate membrane lining the eyelids and covering the edges of the eyeballs) causing inflammation of this (conjunctivitis). The third eyelid is also covered by conjunctiva. In normal cats the conjunctiva is not readily visible and has a pale, salmon pink colour. In cats with conjunctivitis, the conjunctiva becomes swollen and reddened often making it more visible. One or both eyes may be involved. Affected cats initially develop a watery discharge from the eyes which later becomes thicker and is usually a yellow or greenish colour. The eyes are uncomfortable and cats often hold the affected eye/s closed. Most cats remain bright and otherwise well, but some may develop a fever or lose their appetite. Occasionally, snuffles and sneezing may also be seen. In adult cats, infertility can result from infection.

If left untreated, the conjunctivitis and associated discomfort and discharges may persist for several weeks or months during which time the cat is also a source of infection to other cats.

How can Chlamydia be diagnosed?

Chlamydia infection can be diagnosed in several ways with isolation of the organism the method of choice. This involves taking a swab from the eyes which is then placed in special transport media and sent to a laboratory where the virus can be grown in culture and identified. Another option is a blood test for antibodies to the Chlamydia which can be useful in cases where a negative isolation result is received or as a general screening test of catteries or multicat households where conjunctivitis has been a problem.

Are other cats in the household at risk of infection?

Chlamydia is spread by close or direct contact with an infected cat so all other cats in the home may have come into contact with the bacterium and therefore be infected. For this reason, once Chlamydia has been diagnosed, all cats in the household should be treated (see later).

Are my family at risk ?

This is an infection of cats and there is no risk of transmission to people.

Is there any treatment for Chlamydia?

Since Chlamydia is a bacterial infection, it can be successfully treated with a course of oral antibiotics. Treatment should be continued for a minimum of 4 weeks and for at least two weeks 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 all of the household is thoroughly treated.

How can disease 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, vaccination can be carried out, once all of the cats have been treated, to minimise 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.