Your vet has just used the word "chlamydia" about your cat's runny, red eye, and understandably, your mind has jumped somewhere alarming. Here's the genuinely important thing to know before you panic: this isn't the same organism people usually associate with that word, and the older name for this condition feline pneumonitis is actually a documented misnomer that's confused pet parents and vets alike for decades.

Chlamydial conjunctivitis, historically called feline pneumonitis, is an eye infection caused by the bacterium Chlamydia felis, and despite the misleading older name, these bacteria rarely cause pneumonia in cats at all the infection always involves the eye, and only occasionally the nose. It's a genuinely common, treatable condition, especially in kittens and young cats, but it comes with one detail that trips up a lot of pet parents: the treatment course runs considerably longer than the visible symptoms do, and stopping early is one of the most common reasons it comes back.

Key Takeaways

• Chlamydial conjunctivitis in cats is caused by the bacterium Chlamydia felis, a genuinely different organism from the chlamydia species associated with human sexually transmitted infection.
• The older name "feline pneumonitis" is misleading these bacteria rarely cause pneumonia in cats; the infection consistently involves the eye and sometimes the nose.
• Most affected cats are less than a year old, and signs peak 9 to 13 days after onset before gradually subsiding over 2 to 3 weeks.
• Treatment typically runs 4 to 6 weeks, and needs to continue after visible signs disappear stopping early is a common cause of recurrence.
• Azithromycin doesn't appear to be an effective treatment for this specific infection, even though it's commonly used for other feline conditions.
• Rare cases of transmission from cats to people have been reported, so good hygiene, particularly hand-washing, is a sensible precaution while treating an affected cat.

What Is Chlamydial Conjunctivitis in Cats?

Chlamydial conjunctivitis is an infection of the conjunctiva, the membrane surrounding the eye. Different strains of Chlamydia felis and Chlamydia pneumoniae bacteria cause significant eye infections in cats, and the disease is also known by an older name, feline pneumonitis a name that's genuinely misleading, since these bacteria rarely cause pneumonia in cats at all. The infection usually involves the eye and occasionally the nose, with sneezing and nasal discharge appearing in some cases.

It's genuinely worth clarifying something here, since the word "chlamydia" alone can cause unnecessary alarm: this is a species-specific bacterium that infects cats (and occasionally other animals), not the organism associated with human sexually transmitted infection. It's a completely separate biological story, transmitted between cats through close contact, not something with any connection to human reproductive health.

Who Gets Chlamydial Conjunctivitis?

Most affected cats are less than a year old, which makes this genuinely a young-cat and kitten condition more than anything else worth keeping in mind if you've recently adopted a kitten or brought a young cat into a multi-cat household.

What Are the Signs of Chlamydial Conjunctivitis in Cats?

Signs include clear or coloured discharge from the eyes, reddened and swollen conjunctivae in one or both eyes, discharge from the nose, and sneezing. The pattern has a genuinely predictable timeline worth knowing: signs are most severe 9 to 13 days after onset, and then gradually subside over 2 to 3 weeks. That said, in some cats, signs can last for weeks despite treatment, and recurrence is genuinely not uncommon which is exactly why understanding the treatment timeline properly (covered below) matters so much.

How Is Chlamydial Conjunctivitis Diagnosed?

Your vet can confirm the diagnosis by taking a smear from the conjunctiva and identifying the chlamydial organism on laboratory tests or under a microscope. This step genuinely matters, because chlamydial conjunctivitis can look remarkably similar to other, more common causes of feline eye infection including feline herpesvirus, covered in our companion guide on conjunctivitis (pink eye) in cats and identifying the actual organism causing the infection is genuinely essential for choosing an effective treatment, since different causes respond to different medications.

How Is Chlamydial Conjunctivitis Treated in Cats?

Your vet can prescribe antibiotics to treat the infection, and treatment usually lasts 4 to 6 weeks genuinely longer than most pet parents expect for what looks like a straightforward eye infection.

Why the Treatment Timeline Matters So Much

This is the single most important thing to understand about managing this condition well. To reduce recurrence, treatment in cats is usually continued after signs disappear, so even though your cat looks better, be sure to follow the treatment program for the full length of time prescribed. This is exactly the kind of instruction that's genuinely easy to quietly abandon once the obvious redness and discharge have cleared but doing so is one of the more common reasons this infection returns, sometimes weeks or months later.

What Medications Actually Work?

Doxycycline is generally the preferred treatment, though fluoroquinolones (such as enrofloxacin or pradofloxacin) and amoxicillin-clavulanic acid have also been used successfully, albeit possibly with somewhat lower effectiveness than doxycycline. One genuinely useful, specific detail worth knowing: azithromycin does not appear to be effective against this particular infection, even though it's a commonly reached-for antibiotic for other feline conditions which is exactly why it matters that your vet identifies the specific cause before choosing a treatment, rather than defaulting to a familiar antibiotic.

Is There a Vaccine?

Yes vaccines are available for chlamydiosis in cats. It's genuinely important to understand what this vaccine can and can't do: it does not completely protect a cat from infection, but it can significantly reduce the severity and likelihood of infection. This vaccine tends to be most useful in higher-risk settings breeding catteries or shelters, for instance, where eliminating the organism entirely from the environment is genuinely difficult. It's worth discussing directly with your vet whether it makes sense for your specific cat's situation, rather than assuming it's either essential or unnecessary.

Can This Spread to Other Cats or People?

Untreated cats can spread the infection to other cats for months after infection, which is genuinely important to know if you share your home with multiple cats an infected cat who isn't properly treated remains a real, ongoing source of infection for housemates well beyond when their own symptoms might have settled down on their own.

There have also been occasional reports of transmission of the Chlamydia bacteria from cats to people, so frequent hand-washing and other good hygiene measures are genuinely worth practising while treating a sick cat, to reduce the (rare, but real) chance of infection in people. This is worth keeping in perspective it's an occasional, documented occurrence rather than a common risk, but it's a reasonable, low-effort precaution regardless.

Caring for a Cat With Chlamydial Conjunctivitis

• Commit to the full 4-to-6-week treatment course, and specifically continue giving medication even after your cat's eyes look completely normal again — as covered above, this is genuinely the single biggest factor in preventing recurrence.
• If you have multiple cats, ask your vet whether the others should be checked or treated too, since an infected, untreated cat can keep spreading the organism for months.
• Practise good hygiene while treating an affected cat, particularly hand-washing after handling their eyes or applying medication, given the rare but documented potential for transmission to people.
• Don't assume every red, watery eye is this specific infection. Our guide on conjunctivitis (pink eye) in cats covers the other common causes, and a proper vet exam with a conjunctival smear is genuinely the only reliable way to tell them apart.
• If your cat needs eye medication for weeks, our guide to giving cats medicine covers a calm, effective technique that makes a long treatment course genuinely manageable.
• Never substitute a leftover antibiotic or human medication. Our guide on human medicines and pets explains why the specific antibiotic matters here — as covered above, some commonly used antibiotics genuinely don't work against this particular infection.
• Watch the wider picture. Our guide on 10 signs your pet is sick is a useful general checklist alongside anything eye-specific.

FAQ

Is "feline pneumonitis" the same as pneumonia in cats?
No, genuinely not, despite the name this is one of the more confusing historical naming choices in veterinary medicine. Chlamydia felis rarely causes pneumonia in cats at all; the infection consistently involves the eye and sometimes the nose, not the lungs.

Can I catch chlamydia from my cat?
The specific species that infects cats is genuinely different from the one associated with human sexually transmitted infection, so there's no connection there. That said, occasional reports of cat-to-human transmission causing eye infection do exist, which is why good hygiene while treating an affected cat is a sensible precaution.

Why does my cat need antibiotics for 4 to 6 weeks when the eyes looked normal after two?
Because stopping treatment once visible signs disappear is one of the most common reasons this infection returns. Vets specifically recommend continuing the full prescribed course, even after the eyes look completely normal, to genuinely reduce the risk of recurrence.

Do all cats in a multi-cat household need treatment if only one shows symptoms?
It's genuinely worth asking your vet, since untreated infected cats can spread the organism to housemates for months after their own infection. Even cats without visible symptoms may be worth checking in a household where one cat has been diagnosed.

Is the chlamydia vaccine for cats worth getting?
It depends on your cat's specific risk the vaccine doesn't fully prevent infection but can meaningfully reduce its severity and likelihood, and it's most commonly recommended for cats in higher-risk environments like catteries or shelters. It's genuinely worth discussing directly with your vet rather than assuming it applies universally.

References

1. Gelatt, Kirk N. Chlamydial Conjunctivitis in Cats (Feline Pneumonitis). Merck Veterinary Manual, Pet Owner Version.
2. Chlamydial Conjunctivitis in Animals. Merck Veterinary Manual, Professional Version.