Feline chlamydophila disease refers to infection with a type of bacterium called Chlamydophila felis. This was formerly known as Chlamydia psitacci var felis.
Many different strains of chlamydia-type bacteria exist, most being highly species specific (each strain usually only infecting one or a small number of different animals/species).
The bacterium that infects cats is specifically adapted to them, where it primarily causes ocular infections and conjunctivitis. Appropriate treatment can eliminate the organism and resolve all the clinical signs. Where the disease is problematic in colonies of cats, vaccination is also available and can be helpful as part of a control plan.
In keeping with other similar organisms, Chalmydophila felis (or C felis) is a very fragile bacterium and cannot survive for any significant time in the environment. Infection is therefore mainly through direct contact between animals.
What disease does C felis cause in cats?
Chlamydophila felis is mainly a cause of conjunctivitis (infection and inflammation of the delicate membranes – conjunctiva – that cover the inner surface of the eyelids and the white part of the eye itself).
The bacteria invade and infect the cells of the conjunctiva itself causing inflammation and ocular discharge. Clinical signs usually develop within a few days of infection, and starts off as a watery ocular discharge. At first only one eye may be involved, but within a few days the disease invariably affects both eyes. Pain and discomfort means affected cats may hold their eyelids partially closed (blepharospasm) and as the disease progresses, severe swelling and reddening of the conjunctiva may be seen. The discharge changes to a thicker yellowish nature and occasionally the eye infection is accompanied by mild sneezing and nasal discharge. Occasionally there is alao a mild fever which can result in lethargy and inappetence but cats usually remain bright and eat well.
If left untreated, the conjunctivitis can often persists for two months or more, and cats may continue to shed the bacteria in ocular secretions for many months (and thus be a potential source of infection to other cats).
Although C felis mainly causes conjunctivitis, the organism can also be found in the lungs, gastrointestinal tract and reproductive tract. There is some speculation that it may occasionally contribute to infertility in breeding queens.
Which cats are at risk of infection?
Chlamydophila infection is relatively common in cats, and it may be a cause of up to 30% of cases of chronic (long-term) conjunctivitis. However, the organism requires direct contact between cats to spread so disease is much more common where larger groups of cats are kept together (multi-cat households, breeding households, catteries and shelters).
Although cats of all ages can be infected, disease is seen most commonly in kittens 5-12 weeks of age. Chlamydophila also has to be distinguished from other potential causes of conjunctivitis such as feline herpesvirus, feline calicivirus and mycoplasmas. Conjunctivitis may also occur as a result of trauma, allergies or other non-infectious reasons.
Diagnosis of Chlamydophila felis infection
Diagnosis of feline chalmydophilosis requires detection of the organism in the conjunctiva of a cat showing typical signs. Examination of smears from an eye swab under the microscope may give an indication of the presence of infection through observation of typical changes in the conjunctival cells. However, for definitive diagnosis swabs from the eyes of affected cats should be sent to a veterinary laboratory where the organism can be identified through culture or through molecular diagnostic techniques, such as polymerase chain reaction (PCR).
Treatment of Chlamydophila felis
A number of antibiotics can be used to treat C felis infections. A group of antibiotics known as tetracyclines are considered the treatment of choice, being most effective. Doxycycline is one of these antibiotics and only has to be administered once daily to infected cats. Some other antibiotics may also be effective, but these are generally not as good and have to be given for longer to achieve the same results as doxycycline.
Oral treatment with tablets or a suspension is best, as the organism can be present at sites other than the eye, but topical treatment with eye drops or ointments are also helpful – they may enhance recovery and also make the cat feel more comfortable.
Treatment is usually continued for 3-4 weeks to ensure the organism is eliminated (sometimes longer with other antibiotics) and all cats in a house should be treated.
A vaccine is available in many countries to protect cats against chlamydophila conjunctivitis. This does not always prevent infection, but is helpful in preventing severe clinical disease. Although not generally suitable for the majority of pet cats, it can be useful in high risk situations such as catteries with persistent problems with the organism.
Risk to humans from feline chlamydophilosis
Humans can be infected with Chlamydia psitacci, but the bacterium that infects cats (Chlamydophila felis) is highly adapted to this species. There have been one or two reports of human conjunctivitis 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).