Feline Chlamydophila (formerly known as Chlamydia) mainly causes conjunctivitis in the cat. Conjunctivitis may be defined as the inflammation of the delicate membranes or conjunctiva that cover the inner surface of the eyelids and over the white part of the eye (the sclera). However, this infectious organism is not responsible for the full range of signs associated with cat 'flu.
Infection is relatively common in cats, with up to 30% of cases of chronic conjunctivitis caused by this organism. Although cats of all ages can be infected, disease is seen most commonly seen in young kittens (5 - 12 weeks old) with persistent or recurrent infection.
Chlamydophila organisms are very fragile and cannot survive for any period of time in the environment. Infection therefore typically occurs through direct contact and disease is more commonly seen where large groups of cats are kept together, such as multi-cat households, breeding catteries and shelters.
Clinical signs normally develop within a few days after infection, beginning as a watery discharge from one or both eyes. Due to the discomfort, affected cats may hold their eyes 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 substance. There may also be very mild sneezing and nasal discharge in some cats with a mild fever resulting in lethargy. If left untreated, the conjunctivitis can often persist for six to eight weeks or longer and cats may continue to shed the organism for many months.
Chlamydophila infections respond well to a number of different antibiotics. 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).
Vaccines exist to protect cats against Chlamydophila conjunctivitis. These vaccines do not always prevent infection, but are certainly helpful in preventing severe clinical disease. Its use can be recommended in high risk situations, but should not be part of a standard vaccination regime.
Humans can be infected with Chlamydia but the organism 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 Chlamydophila 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).