Feline Chlamydophila Disease, often called Chlamydiosis, is caused by an infection with the Chlamydophila felis (C felis) bacterium. Many strains of chlamydia bacteria exist, and most are relatively species specific, meaning they only infect one species of animals. C felis is a strain highly adapted to cats, so rarely affects other animals. This disease affects cats of all ages, but is most common in kittens 5-12 weeks of age.
Upon initial infection, C felis targets the conjunctival epithelium (lining of the lids of the eyes). The bacteria replicate in these epithelial cells, causing the cells to rupture and release the infectious bodies to other nearby epithelial cells and, eventually, epithelial cells throughout the body.
In cats, C felis primarily causes conjunctivitis: infection and inflammation of the membranes lining the eyelids. Usually both eyes are affected. Cats develop signs within a few days or up to a week after infection. You'll generally notice a watery discharge from one or both eyes at first. Your cat will be in a great deal of discomfort, so may blink more than usual or hold the eyelids partially closed. As the condition worsens, you may see severe swelling and reddening of the lining of the lids, along with a thicker yellow discharge.
Some cats also display mild nasal discharge, sneezing, mild fever, lethargy, or loss of appetite. Rarely, cats can develop a more serious feline upper respiratory disease from C felis. (Feline herpes virus and calicivirus infections, however, are the causes in more than 90% of the cases of feline upper respiratory disease; C felis is the cause in less than 10% of the cases.) Lameness may be associated with the chlamydiosis, as well.
Chlamydophila felis cannot survive outside of its host, so generally there is no threat of acquiring it from the environment. Transmission requires close contact between cats, but can include things like an infected cat sneezing on another cat; therefore, cats living in shelters, catteries or rescue homes are typically more at risk for this disease.
Diagnosis requires laboratory testing of a swab taken from the affected eyes (sometimes swabs are taken from other areas, as well).
Feline Chlamydiosis usually responds quickly to antibiotics, primarily tetracyclines. Doxycycline is often prescribed, since it can be given only once daily. Topical therapy with eye drops or ointment is usually recommended, also, but should be used only in combination with oral antibiotics, as the bacteria can be present at sites other than the eyes. The eyes and nostrils should be gently cleaned and kept free of discharge. In some cases, especially if the cat is also infected with feline immunodeficiency virus (FIV), the infection can become chronic.
Vaccination should be considered for cats at risk of exposure to infection, i.e. cats living in shelters or rescue homes where there has been a confirmed infection of C felis. Vaccination generally begins at 8-10 weeks of age, with a second injection 3-4 weeks later. Annual boosters are recommended for cats at continued risk of exposure. Though vaccination does not prevent infection, it is helpful in enhancing the animal's immune response and minimizing the severity of clinical signs.
There has been an isolated report of a human eye infection with C. felis, but in almost all cases chlamydiosis in people is caused by different strains of the bacteria.