Here's what you need to know about this bothersome bug.
By Janet Foley, D.V.M.
You may think of chlamydia as a sexually transmitted disease that humans get, but there are many strains of this bacteria, one of which causes upper respiratory infections (URIs) in cats. The chance of a cat giving you chlamydia is low, and even if you did pick it up, the infection would be in your eyes, triggering conjunctivitis. (But more on protecting people later.)
Chlamydia bacteria can live in the respiratory, genital, urinary, and digestive systems of several animals. The species of chlamydia that infects cats is Chlamydia psittaci. Though a less common cause of URIs than allergies and such viruses as feline herpes and calicivirus, this chlamydia strain typically gives cats swollen conjunctivae (whites of the eyes) and lots of thick green discharge, but no fever or signs of whole-body illness such as reluctance to eat or lethargic behavior. (The exception is kittens, who won't eat if they can't smell their food, so any condition that includes a stuffy nose may keep them from eating.)
Young cats or those with impaired immunity may develop severe lung infections, sometimes referred to as chlamydia pneumonitis. If your cat has an underlying condition such as feline leukemia, feline calicivirus infection, or FIV, there's a higher risk he'll pick up a chlamydia infection if exposed.
Your veterinarian will confirm a chlamydia diagnosis with a bacterial culture or by using a special antibody stain on a swabbed sample from the eyes.
Antibiotics are placed in the eyes or given by mouth. The antibiotic of choice for chlamydia is tetracycline, and you can usually get away with directly applying a tetracycline ointment specially made for the eyes. (For lung infections, tetracycline needs to be given by injection or pill.) However, some animals can't take tetracycline because they're sensitive or allergic to it, and the drug is slightly irritating, so it may redden their eyes. If the eyes are treated repeatedly and stay red, the cat might do better without the ointment. Your veterinarian will then consider other ointments or perhaps oral tetracycline.
Eye ointments that contain steroids need to be used with extreme caution, as they can be a recipe for disaster in a cat who's incubating chlamydia. (Vets often use steroids in any irritated eye without first getting a good diagnosis.)
If your cat becomes dehydrated (ask your vet what signs to watch for), stops eating, or develops a fever, subcutaneous fluids, appetite stimulants, and possibly antihistamines may be necessary. If signs don't improve or only partly improve, chances are the cat has a virus as well - something your vet will need to address. If the bacteria is partially drug resistant, your vet may need to culture a sample and test which antibiotics work best.
With the right antibiotic therapy, your cat should improve rapidly, although it's usually recommended to continue the treatment for at least three weeks. If the response is partial or poor, your cat probably has a viral infection, too (your vet will need to investigate). Unfortunately, chlamydia can be chronic, in which case your cat could relapse after the antibiotics are discontinued.
Management and Prevention
The two most important measures for preventing URIs in general are to make sure your cat gets regular vaccinations and to avoid exposure to infected cats. The commonly used three-way vaccine (FVRCP) partially protects the cat from calicivirus and herpesvirus, which means less likelihood of severe chlamydia infection.
In large groups of cats, such as in shelters and breeding catteries, I recommend the use of killed vaccines because otherwise - with a modified-live vaccine - the group will typically have the sniffles and eye discharge 10 days after they get the shot. There's a modified-live chlamydia vaccine on the market, but it can cause upper respiratory symptoms, it's only moderately effective, and there's a risk of side effects.
You'll want to isolate any cat who has a particularly bad URI in a disinfected environment that maintains excellent airflow. Also, using a disinfectant such as bleach or Lysol, frequently clean any area in which the affected cat spends time.
Good-health guidelines - both for well cats and for cats with chlamydia - are to keep cat numbers low, reduce exposure to irritants such as cigarette smoke, to provide premium food and fresh water, and to get any medical condition treated promptly.
If your cat has a bad chlamydia infection, keep him away from young children and anyone with a compromised immune system. And wash your hands after you touch your cat.
One last warning: If you also have a pet bird, you should know that it's possible - though rare - for birds to pass C. psittaci to cats. Your bird, if carrying the bacteria, could also give you psittacosis. If you have any reason for concern, discuss the matter with your vet - and meanwhile, wash up frequently.