Moderate severity

Feline Chlamydiosis (Chlamydia felis)

A bacterial infection caused by Chlamydia felis and one of the leading causes of persistent conjunctivitis in cats — especially kittens — producing sore, weepy, swollen eyes that often start in one eye and spread to the other.

⚠️ Common symptoms

Red, swollen, watery eyes (conjunctivitis), often starting in one eyeA discharge that turns from watery to thick and yellow-greenSwelling of the pink conjunctival membrane around the eyeSquinting and discomfort in bright lightMild sneezing or nasal discharge in some catsA low-grade fever or slight dip in appetite early on

Feline chlamydiosis is an infectious disease caused by the bacterium Chlamydia felis, and it is one of the most common infectious causes of conjunctivitis — inflammation of the membranes around the eye — in the cat. It has a particular fondness for the eyes, and the typical patient is a young kitten in a home, shelter, or cattery where cats live in close contact.

The illness usually begins in one eye. The conjunctiva — the pink lining around the eyeball and inside the lids — becomes red, swollen, and sore, and the eye waters. Within a few days the second eye is often involved too, and the discharge, watery at first, thickens and takes on a yellow-green colour as the infection develops. Affected cats squint and are clearly uncomfortable, and some show mild sneezing, a runny nose, or a slight fever, though chlamydiosis is primarily an eye disease rather than a full respiratory one.

Because several agents can cause conjunctivitis in cats — including feline herpesvirus and calicivirus — a vet may take swabs to confirm Chlamydia felis, especially where cases keep recurring in a group of cats. The good news is that the bacterium responds well to antibiotics. A multi-week course of oral doxycycline is the usual treatment, and it is important to complete the full course, because stopping as soon as the eyes look better can leave a lingering infection that flares again. In multi-cat households it is common to treat everyone together, since the organism passes so easily between cats. With prompt, complete treatment and sensible hygiene, the outlook is very good, and vaccination is available to reduce severity in high-risk settings.

🔍 Causes

The infection is caused by the bacterium Chlamydia felis (formerly Chlamydophila felis), which mainly targets the delicate membranes of the eye. It spreads through direct contact with eye secretions from an infected cat, so it passes easily in multi-cat homes, shelters, and breeding catteries. Kittens between about five weeks and nine months old are the most commonly and severely affected.

🛡 Prevention

Good hygiene and reducing overcrowding limit spread in multi-cat environments, and new or sick cats should be isolated until treated. A vaccine against Chlamydia felis is available and is often recommended for cats in high-risk settings such as catteries and shelters; it reduces the severity of disease rather than preventing infection outright.

💊 Treatment

Chlamydiosis responds well to antibiotics, most often a course of oral doxycycline given for several weeks — long enough to fully clear the organism, as stopping early can allow relapse. Topical eye ointment may be used alongside. Because the bacterium spreads readily between cats, all cats in the household are usually treated at the same time.

When to see a vet: See a vet for any cat with a persistently red, weepy, or swollen eye, particularly a kitten or a cat from a multi-cat home, so the cause can be identified and treated. Early antibiotic treatment shortens the illness and stops it spreading to other cats.

⚕️ Medical disclaimer

  • This information is educational only and is not a substitute for veterinary advice.
  • Symptoms overlap between conditions — only a vet can diagnose accurately.
  • Never withhold treatment or self-medicate based on information found online.
  • When in doubt, call your vet. Early intervention almost always leads to better outcomes.

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