Feline Chlamydia (Chlamydophila felis) infection

Feline Chlamydia disease refers to infection with a type of bacterium called Chlamydophila. Many different strains of Chlamydia type bacteria exist. In general they are highly species-specific - i.e. each strain usually infects one or a small number of different animals. The bacterium that infects cats, known as Chlamydophila felis, appears to be highly adapted to the cat and rarely, if ever, causes disease in other animals. Chlamydia organisms are very fragile and cannot survive for any significant period of time in the environment. Infection therefore occurs through direct contact between animals.

Chlamydia life cycle

Chlamydia inclusions bodies within cells

Chlamydia infection in kitten and adult cat

Symptoms

In cats, Chlamydia mainly causes conjunctivitis (infection of the eyelids). Clinical signs usually develop within a few days to a week after infection and usually begin as a watery discharge from one or both eyes. Although sometimes only one eye is affected when signs first develop (usually the left eye), within a few days both eyes become involved. Due to the discomfort, affected cats may hold their eyelids partially closed. As the disease progresses, severe swelling and reddening of the conjunctiva may be seen and the discharge changes from watery to a thicker yellowish discharge. Although conjunctivitis is the major clinical sign, there may also be mild sneezing and nasal discharge in some affected cats. Occasionally there is a mild fever which can result in lethargy and inappetence but, generally, affected cats remain bright and eat well. If left untreated, the conjunctivitis often persists for six to eight weeks or longer and cats may continue to shed the organism for many months. Although mainly a cause of conjunctivitis, Chlamydia has also been found in the lungs, gastrointestinal tract and reproductive tract of cats. It is a leading cause of infertility (failure to conceive), repeat heats, metritis/pyometron (infection of the uterus) and can also localise in joints, causing arthritis.

Chlamydia infection is relatively common in cats and up to 30% of cases of chronic conjunctivitis may be caused by this organism. However, because the organism does not survive in the environment and requires direct contact between cats to spread, disease is much more commonly seen where larger groups of cats are kept together, such as multi-cat households, catteries and shelters. Although cats of all ages can be infected, disease is seen most commonly in young kittens (5 - 12 weeks old) with persistent or recurrent infection. Some cats can be infected with both cat flu and Chlamydia.  

Diagnosis

Because Chlamydia can be confused with cat flu, the only way to accurately diagnose this disease is by having your vet take a swab of the eye and having it cultured. Because of the difficulty in isolating Chlamydia from swabs taken from the cat, it is better to assume an infection exists and to treat with antibiotics rather than risking spreading the disease.  

Treatment

Chlamydia is transmitted between cats by direct contact (including sexual) or by aerosol (sneezing), nasal discharges and from soiled paws (wiping away discharge from eye/nose). In breeding situations, physical transmission by humans is also possible.

Chlamydia infections respond well to a number of different antibiotics. A group of antibiotics known as tetracyclines have generally been considered the treatment of choice for Chlamydia in cats. Certain other antibiotics may also be effective, but have to be chosen carefully as a number of antibiotics are completely ineffective against the organism. Topical therapy with eye drops or ointment is usually recommended, but this should be combined with systemic (oral) therapy as the organism can be present at sites other than just the eyes. If giving eye drops is difficult, infections will still respond well to oral therapy alone. Generally, treatment is recommended for a period of four weeks and all cats in the household should be treated (irrespective of whether they are showing clinical signs). Care has to be taken treating pregnant cats and young kittens (giving tetracyclines during development of the teeth can lead to their discolouration) and at this time other antibiotics may be used.

Zithromax® is a new , safe antibiotic which is highly effective against Chlamydia. Vibravet® takes four weeks of daily tablets to wipe out Chlamydia; Zithromax does it in a single dose.  It is very safe and it works well. It is available in both liquid and tablet form. The dose of Zithromax for cats in 20mg Zithromax per kg body weight or 80mg orally as a single dose, given once or twice weekly for 3-6 weeks. 

Prevention

A vaccine exists to protect cats against Chlamydia conjunctivitis. The vaccine does not always prevent infection, but is certainly helpful in preventing severe clinical disease. Its use can be recommended in high risk situations.

Zithromax has a 99.9% kill rate with Chlamydia bacteria, but there is no guarantee that the cats treated are completely cured. However, after a three week course, most cats are assumed to be Chlamydia free. I have found from experience though, that some cats will have a recurrent infection some time in the future, especially if they get stressed (sometimes a year or two later). Whether this is from a cat who is not completely cured or from a new infection is not known, but wherever the infection has come from, some cats seem to be more prone. Unfortunately with Chlamydia, there is no total cure, like there is with other diseases, where once they get over an infection, they are immune for the rest of their life. The reason for this is that Chlamydia is caused by a bacteria not a virus.
Still, this reinfection rate with Chlamydia in cats is very low, and for all intents and purposes, you can assume that a three week course will completely eradicate the disease from your cats. A four week dose of Zithromax is sometimes used when selling cats, more for legal reasons rather than anything else.

Humans can be infected with Chlamydia but the bacterium that infects cats, Chlamydophila felis, is highly adapted to this species. There have been one or two reports that have suggested human conjunctivitis has occurred following contact with a cat harbouring C felis, but the risk appears to be extremely low. Routine hygiene precautions are recommended when handling and treating infected cats (washing hands after stroking or giving medications and avoiding close face-to-face contact until the infection has resolved).