Chlamydia is a bacterial infection that causes conjunctivitis (sore, swollen eyes with a white discharge) and very occasional breathing problems. It most commonly causes disease in cats that live in groups. Chlamydia is passed from cat to cat via the aerosol route. It primarily affects young kittens around 2 months of age but can be seen in older animals with underlying diseases or impaired immune function.

Kittens usually have immunity to chlamydia from their mother for the first 6-8 weeks of life. However, the bacterium is common in the environment and when kittens lose their immunity, they often become infected. The bacteria begin to grow in the conjunctiva of the eye and a discharge develops. The discharge is often clear to start with but soon becomes thicker and yellowish.

Infections are more common in cats from multi-cat homes – particularly catteries. The infection is spread through the air and so cats in close contact are exposed to more bacteria. Some cats become chronically infected and although may show minimal signs themselves continually shed bacteria into the environment posing a health risk to other cats.

The signs of chlamydia infection are very obvious, usually there is redness and swelling of the eyelids. Excess tear production and colored discharges from the eyes are common. Occasionally kittens are more severely affected and may have coughing, sneezing or difficulty breathing. If left untreated signs may take several months to resolve. In some cats the disease is not completely cured at this point and the bacteria may persist in the cat only to cause a further outbreak of signs in later life if the cat suffers with a reduced immune system.

Your veterinarian may suspect that your cat has a chlamydia infection just by looking at their eyes. A sample of the bacteria can be simply collected by rolling a moist swab across the surface of the eye. Rapid tests can confirm the presence of bacteria in the swab, but a final diagnosis may require the sample to be sent away for further testing.

A blood test can be done to look for antibodies to the infection. However, this only confirms previous exposure to the bacterium and not an active infection.

Your veterinarian will want to rule out other causes of conjunctivitis especially feline herpes virus and calicivirus (components of cat flu) and other causes of discharging eyes of which there are many. It is important to rule out the possibility that there is a foreign body (such as a grass seed) in the eye, and allergies and exposure to irritants can also cause similar signs.

Initial supportive care requires cleaning secretions from the face and bathing the eyes. Eye creams containing tetracycline antibiotics can be applied and, in chronically infected animals, antibiotics may need to be given by mouth. Most cats recover quite quickly although may go on shedding bacteria for 2 months (and in some cases for up to 7 months).

There is a vaccine available but there is probably little value in using this in individual cats. Vaccination does not always prevent infection, but it usually stops severe disease developing. Vaccinated cats may still therefore carry infection and can pass it on to susceptible cats. In a cattery the vaccine can be useful to reduce infection of other cats. The vaccine is not given as a part of the routine course, and you should discuss with your veterinarian whether your cat needs to have the vaccination.

If your cat lives in close proximity to other cats, then hygiene is very important to reduce the transmission of all diseases. Good ventilation is important and there should be air spaces between all cages to prevent droplets being carried in the air between cats.

The type of chlamydia affecting cats is very adapted to living in cats and rarely affects other species. However, there have been one or two reports of people who have handled infected cats developing conjunctivitis themselves. When handling a sick cat, you should always take careful hygiene precautions and pay particular care to hand washing. The disease is very contagious and can easily be spread from cat to cat.

If you have any concerns about your cat, contact your own veterinarian for further advice.