Dog & cat health · Vet-reviewed guide

Cat Eye Infection Chlamydia: The Bacterial Cause and Its Treatment

When a cat's eye infection just won't quit, one bacterial cause is often behind it — and unlike the viral kind, this one actually responds to antibiotics.

Quick answer: A cat eye infection from chlamydia is caused by the bacterium Chlamydia felis, and the good news is that, unlike a viral herpes flare, it responds to antibiotics. It typically shows up as a persistent conjunctivitis: red, swollen eyelids and a watery-to-goopy discharge, often starting in one eye and spreading to the other.

Because it is bacterial, a vet-prescribed antibiotic clears it, but two things make it different from a routine infection: the treatment course is long, usually around four weeks, and every cat in the household normally needs treating, because the bacteria spread easily between cats. Stopping early is the main reason it comes back. There is also a small human-transmission risk, so hand-washing matters. If your cat has a stubborn, weeks-long red eye, see a vet to get it properly diagnosed and treated.

Signs of chlamydial conjunctivitis

The hallmark is a conjunctivitis that lingers: reddened, swollen eyelid linings, squinting, and a discharge that ranges from watery to thick.¹ It often begins in one eye and moves to the second a few days later. Young cats and those from multi-cat environments like shelters are most commonly affected. Some cats also have mild sneezing or nasal signs.

Why it is different from a herpes eye infection

This distinction matters for treatment. A herpes eye infection is viral, so antibiotics do not touch the virus itself. Chlamydia is bacterial, so antibiotics are exactly the right tool.² The two can look similar to an owner, which is why a vet diagnosis, sometimes with a lab test, is what points to the correct treatment.

How it is treated

Treatment is a course of antibiotics prescribed by a vet, commonly an oral course, sometimes alongside topical eye treatment.² Two rules make or break it:

• Finish the full course. Chlamydia needs several weeks of treatment, and stopping when the eye looks better lets it return.
• Treat every cat in the home. Because it spreads between cats, treating only the sick one usually leads to reinfection.¹

The specific antibiotic and dose have to be chosen by a vet for your cat. If your cat needs a prescription, our licensed veterinarians can review your cat and issue one when appropriate. See how our vet prescription service works.

The human-transmission angle

Feline chlamydia is mainly a cat-to-cat problem, but rare cases of human eye infection have been reported, usually after close contact with an infected cat.¹ The risk is low, and simple hand-washing after handling your cat or cleaning its eye reduces it further. If you want the fuller picture on what does and does not spread, see our guide on whether cat pink eye is contagious.

When to see a vet

See a vet for any eye infection that lasts more than a day or two, spreads to the second eye, or comes with squinting or heavy discharge, and sooner if the eye is painful or held shut.² A stubborn, weeks-long conjunctivitis is a classic reason to test for chlamydia specifically.