Chlamydial Conjunctivitis in Cats

By Malcolm Weir, DVM, MSc, MPH; Tammy Hunter, DVM; Ernest Ward, DVM

What is feline chlamydial conjunctivitis?

Feline chlamydial conjunctivitis is an infection caused by the bacterial organism Chlamydophila felis. The most common signs of chlamydia in cats involve the eyes or the upper respiratory tract (nose or throat) and can spread to the lungs if left untreated. This bacteria has also been reported to infect the genital tract and joints.

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, the spread of infection relies on direct or close contact with an infected cat. Following infection, the incubation period (the time between infection and development of clinical signs of disease) is between three and ten days.

Which cats are most at risk for 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 are the clinical signs?

The bacteria primarily infect the conjunctiva, which are the delicate membranes lining the eyelids and covering the edges of the eyeballs. The infection causes inflammation known as conjunctivitis. In healthy cats, the conjunctiva is not readily visible and has a pale pink color. In cats with conjunctivitis, the conjunctiva becomes swollen and red, making it more visible. The nictitating membrane (third eyelid in the inner corner of the eye) may protrude partially across the eye. One or both eyes may be affected.

Affected cats initially develop a watery discharge from the eyes that quickly becomes thicker and is usually a yellow or green color. The eyes are uncomfortable, and cats often keep the affected eye(s) closed. Many 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 kittens, the infection may spread to the lungs and cause fatal pneumonia.

"In kittens, the infection may spread to the lungs and cause fatal pneumonia."

If left untreated, conjunctivitis and the associated discomfort and discharge may persist for several weeks or months, during which time the cat is a source of infection to other cats. Infected cats may appear to recover and then develop a relapse.

How is chlamydial conjunctivitis diagnosed?

Chlamydial conjunctivitis can be difficult to diagnose because there are many causes of conjunctivitis and cats may have multiple infections at the same time. A swab sample from the conjunctival membrane can be sent to a laboratory where the sample is grown in culture and subsequently identified. This test, however, tends to be inaccurate.

The preferred diagnostic option is PCR (polymerase chain reaction) testing of conjunctival scrapings and swabs for evidence of chlamydia antigens (proteins).

How is chlamydial conjunctivitis treated?

Chlamydia can be successfully treated with a course of oral and topical antibiotics. Only certain antibiotics can penetrate inside the cells where the bacteria live. Treatment must be continued for a minimum of four weeks and for at least ten days after the eyes appear normal.

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 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.

Are other cats in the household at risk of infection?

Chlamydia is spread by close or direct contact with an infected cat, so all cats in the home can become infected. For this reason, if one cat in the home is diagnosed, all cats in the household should be treated.

"...if one cat in the home is diagnosed, all cats in the household should be treated."

How can chlamydial conjunctivitis be prevented?

Various vaccines are available and are most useful in breeding catteries or animal shelters where it can be difficult to eliminate the organism completely. This vaccine is considered “non-core” and will be recommended if your cat is at reasonable risk for contracting the disease. The protection afforded by the vaccine is relatively short, and annual boosters are usually required. Your veterinarian will advise you on the appropriate vaccination choices for your cat, based on the prevalence of this disease in your area and your cat’s individual risk.

Can I get this infection from my cat?

There are isolated reports of people who live in the same household as affected cats developing feline chlamydia-associated conjunctivitis. Therefore, if anyone in your household develops sore or runny eyes, they should consult their doctor and report that there is a chlamydial infection in the household cat. Such infection is extremely uncommon and, once diagnosed, is readily treatable.

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