Cats get chlamydia through close, direct contact with an infected cat. The bacterium responsible, Chlamydia felis, spreads primarily through eye and nasal secretions. It is not the same organism that causes chlamydia in humans, and it has nothing to do with sexual contact. Cats most commonly pick it up in environments where they share space with other cats, such as shelters, catteries, and multi-cat households.
How the Bacteria Spreads Between Cats
Chlamydia felis lives inside cells, particularly the cells lining the eyes and, to a lesser extent, the respiratory tract. When an infected cat produces eye discharge or sneezes, the bacteria can travel in those droplets to a nearby cat. Face-to-face contact is the most efficient route because the bacteria needs to reach the mucous membranes of the eyes or nose to establish infection. Cats that groom each other, share food bowls, or simply sleep close together are at higher risk.
The organism is fragile outside a living host. It survives poorly on surfaces, bedding, or toys compared to hardier viruses like calicivirus. This means contaminated objects are a less likely source of infection, though freshly soiled items could theoretically carry enough bacteria to matter. The practical takeaway: direct cat-to-cat contact is the primary concern, not environmental contamination.
Which Cats Are Most at Risk
Kittens and young cats under nine months of age are the most frequently affected group. Their immune systems are still developing, and they tend to be in environments with lots of other cats during the early months of life, whether in a litter, a foster home, or a shelter. Adult cats can absolutely become infected too, but clinical disease is more common in younger animals.
Multi-cat environments are the biggest risk factor. Shelters, breeding catteries, and households with several cats create the close quarters that Chlamydia felis needs to jump from one host to another. A single indoor cat with no exposure to other cats has very little chance of encountering the bacteria. Outdoor cats that interact with strays or neighborhood cats face a moderate risk, especially during nose-to-nose greetings.
Cats already dealing with another upper respiratory infection, such as feline herpesvirus, are more vulnerable. A weakened immune response or already-inflamed eyes and airways give the bacteria an easier foothold. Stress from overcrowding, rehoming, or boarding can also lower a cat’s defenses and make infection more likely to take hold.
What Infection Looks Like
After exposure, symptoms typically appear within 3 to 5 days. The hallmark sign is conjunctivitis, an inflammation of the membranes around the eyes. It usually starts in one eye and spreads to both within a few days. You’ll notice watery discharge that gradually becomes thicker and yellowish-green, along with redness, squinting, and swelling of the tissue around the eye. The third eyelid (the small membrane in the inner corner) often becomes visibly red and puffy.
Some cats develop a mild fever, lose interest in food, or drop a small amount of weight early in the infection, but most continue eating and behaving relatively normally. Sneezing can occur, though it’s typically mild. Chlamydia felis is primarily an eye pathogen, not a respiratory one, which is one way vets begin to distinguish it from other common upper respiratory infections in cats. If your cat has significant sneezing and nasal congestion with only mild eye involvement, a virus is the more likely culprit.
Without treatment, the conjunctivitis can persist for weeks or even become chronic. Some cats become carriers after recovery, shedding the bacteria intermittently without showing obvious symptoms. These carriers are a major reason chlamydia circulates in multi-cat environments; a cat can look perfectly healthy and still pass the infection along.
How Vets Confirm It
Because the eye symptoms of chlamydia overlap heavily with viral infections like herpesvirus and calicivirus, a definitive diagnosis requires testing. PCR testing on an eye swab is the preferred method. It’s highly sensitive and doesn’t depend on keeping the bacteria alive during transport to a lab, which older culture methods struggled with. The swab needs to collect some actual cells from the surface of the eye, not just discharge, because the bacteria lives inside cells. A vet may apply a drop of local anesthetic to the eye before swabbing to make the process more comfortable.
Treatment and Recovery
Chlamydia felis responds well to antibiotics. Treatment typically involves oral antibiotics given daily for several weeks. Eye drops or ointment containing antibiotics are often used alongside the oral medication to address the conjunctivitis directly. Most cats show noticeable improvement within the first week, but finishing the full course of treatment is important to clear the infection and reduce the chance of the cat becoming a chronic carrier.
In multi-cat households, all cats in the home are generally treated at the same time, even if only one is showing symptoms. This prevents the bacteria from ping-ponging between treated and untreated animals.
Prevention in Multi-Cat Settings
A vaccine for Chlamydia felis exists and is available as part of some combination vaccines. It doesn’t prevent infection entirely, but it reduces the severity of symptoms. Vaccination is generally recommended for cats in higher-risk situations, like those entering a cattery, shelter, or multi-cat household, rather than for every cat. For a single indoor cat with no contact with other cats, most vets consider it unnecessary.
If you’re introducing a new cat to your home, keeping them in a separate room for at least a week gives you time to watch for signs of eye infection or upper respiratory illness. This quarantine period covers the typical 3-to-5-day incubation window. Washing your hands between handling the new cat and your resident cats is a simple precaution that helps, even though surface transmission is less common.
Can Humans Catch It From Cats?
Chlamydia felis is not the same species as the chlamydia that causes sexually transmitted infections in people. Cat-to-human transmission has been documented in rare cases, typically causing mild conjunctivitis (pink eye) in the person. The risk is very low for most people, but anyone with a weakened immune system should take basic hygiene precautions when handling a cat with active eye discharge: wash your hands afterward and avoid touching your own eyes.