Mycoplasma conjunctivitis in cats – symptoms and treatment

When to see a vet urgently

Contact a vet promptly if eye symptoms are accompanied by any of the following:

Your cat keeps the eye closed or squints severely because of pain.
The clear surface becomes cloudy or visibly damaged.
Breathing is difficult or your cat breathes with their mouth open.
Your cat is clearly lethargic and does not eat.

Overview

Mycoplasma felis is an opportunistic organism that may form part of a cat's normal upper respiratory microbes. When immunity declines or a viral infection is present, the bacterium multiplies and inflames the eye's mucous membrane. Mycoplasma conjunctivitis can be acute or chronic, often recurs and is frequently associated with respiratory symptoms.

The conjunctiva is the mucous membrane lining the eyelids and covering the white of the eye. The third eyelid at the inner corner may also become red and swollen. The cornea is the transparent surface at the front. Conjunctivitis and a corneal ulcer are different conditions, although they can occur together.

Finding Mycoplasma does not always mean it causes the symptoms. It is also detected in cats without signs. Mixed infection is possible, but eye inflammation alone does not demonstrate concurrent herpesvirus and calicivirus infection or general immune deficiency.

Causes

The condition develops through a combination of factors:

Mycoplasma felis infection through contact with infected animals;
bacterial activation alongside viral infections such as FHV-1 and FCV;
reduced immunity after stress, disease or becoming chilled;
crowded conditions in breeding establishments or rescue centres.

Spread occurs particularly through close contact, respiratory secretions and mutual grooming. Mycoplasma survives poorly in the environment, but other concurrent cat flu pathogens can also travel on hands and objects. Becoming chilled alone does not establish the cause.

Risk factors

Kittens and young cats, with developing immunity.
Cats in multi-cat homes.
Cats positive for FeLV or FIV.
A recent respiratory infection.
Stressful events, such as moving home, surgery or a change of owner.

These factors partly describe the general risks of cat flu and conjunctivitis. An equally precise list has not been established for Mycoplasma eye inflammation in every cat population. Adults of any breed can also be affected. Severe or recurrent signs warrant broader investigation, but not every cat with eye symptoms needs every infectious disease test.

Typical symptoms

Conjunctival redness and swelling.
Eye discharge containing mucus and pus.
Eyelids sticking together after sleep.
Increased watering.
Light sensitivity, frequent blinking or squinting.
Itching and discomfort, with pawing at the eyes.
Coughing, sneezing and nasal discharge with mixed infections.

Inflammation can affect one or both eyes. You may notice a swollen third eyelid appearing from the inner corner. Discharge colour or thickness alone does not identify the cause: similar discharge occurs with several infections and other eye diseases.

If cat flu is present, nasal congestion can reduce smell and appetite. Mouth ulcers may also make eating difficult. Describe eye signs, breathing and feeding separately to the practice because deteriorating general health may require more than topical eye treatment.

Complications and consequences

Without treatment, Mycoplasma conjunctivitis can lead to:

chronic eye inflammation;
corneal inflammation, or keratitis;
corneal ulcers and impaired vision;
secondary bacterial infections;
a recurrent chronic form.

The list describes possible consequences of eye inflammation, rather than the prognosis for every Mycoplasma finding. Herpesvirus, corneal damage and other concurrent factors particularly influence ulcer development. An eye held tightly closed or new cloudiness needs urgent investigation. A small surface injury may be painful without being visible to you.

Diagnosis at the vet

Diagnosis uses:

clinical examination of the eyes and mucous membranes;
cytology of a conjunctival smear to look for mycoplasmas;
PCR, the most accurate method;
bacterial culture to rule out other infections;
viral tests for FHV, FCV, FeLV and FIV.

PCR looks for microbial genetic material and is sensitive. It may also detect material from dead bacteria. A positive result is interpreted alongside symptoms, the sampling site and other findings. Smear cytology can help assess inflammation but does not always identify the cause reliably on its own. Ordinary bacterial culture does not replace Mycoplasma testing because growing it requires special conditions.

Treatment and follow-up

Treatment targets the confirmed or strongly suspected cause. The vet chooses an antibiotic effective against Mycoplasma; not all antibiotics work because the bacterium lacks a cell wall. Oral treatment may be prescribed alongside topical eye medication where needed. Concurrent herpesvirus eye disease may require an antiviral. An antibiotic does not itself treat a virus.

Do not start an old eye medicine yourself for new redness. Corticosteroid preparations in particular can delay corneal ulcer healing and worsen damage. The vet also assesses pain relief and whether a protective collar is needed if your cat rubs the eye. A collar prevents further paw injury but does not treat infection.

If a corneal ulcer is also found, lubrication and monitoring surface healing may be part of treatment. A deep or poorly healing lesion may require assessment by a vet experienced in eye disease and sometimes surgery. Simply changing antimicrobials does not resolve a structural eye problem.

Eye care at home

Ask for a practical demonstration of medicine administration. Wash your hands before and after handling. Discharge around the eye can be gently softened with a clean cloth dampened with warm water. Do not rub the eye surface. Keep the bottle tip away from the eye, eyelids and other surfaces to avoid contamination.

Calm handling and a helper where needed make administration easier. Contact the treating vet if you cannot give the medicine or the eye becomes more painful or red afterwards. Do not shorten the prescribed treatment simply because discharge decreases. If signs do not improve as expected, the diagnosis and any concurrent eye disease are reassessed.

Offer appetising food to a cat with respiratory symptoms and monitor eating and drinking. Food can be warmed slightly to strengthen its smell. Failure to eat, dehydration or breathing difficulty may require hospital supportive care. Wiping away discharge alone is then insufficient.

Prognosis and recurrence

The outlook depends on whether inflammation is confined to the conjunctiva or also affects the cornea or respiratory tract. Lack of response does not automatically mean antibiotic resistance: an incorrect original diagnosis or persistent irritation can also maintain symptoms. In a herpesvirus carrier, another episode may reflect reactivation rather than a new Mycoplasma infection.

Prevention

Reduce stress and support wellbeing and immunity.
Vaccinate against cat flu viruses, including herpesvirus and calicivirus.
Keep the environment clean and avoid crowding.
Check the eyes regularly and see a vet promptly at the first signs.
Have viral and bacterial respiratory infections treated in good time.

There is no vaccine against Mycoplasma felis. Cat flu vaccination reduces disease from other pathogens but does not provide complete protection against every infection. Separate an affected cat from healthy cats as instructed, maintain hand hygiene and clean secretion-contaminated surfaces. Infection management is particularly important when several cats in a home have symptoms.

Important for cat owners

Mycoplasma conjunctivitis is often part of a wider cat flu problem and rarely an isolated disease. Remember that even apparently ordinary conjunctivitis may indicate reduced immunity and viral infection. Timely veterinary attention helps avoid chronic complications and protects eye health.

This article provides general information and does not replace veterinary care. If you notice signs of illness in your cat, contact a vet.

Frequently asked questions

Does a positive PCR prove Mycoplasma conjunctivitis?

Not alone. Mycoplasma can also be found in a symptom-free cat. The vet combines the result with the eye examination and other findings before choosing treatment.

Can it spread to other cats at home?

Yes. Close contact can spread Mycoplasma and other cat flu pathogens. Keeping the affected cat separate and washing hands reduce exposure; the need to examine other cats is assessed individually.

Can I use eye drops left over from last time?

Do not start them without veterinary instructions. A new eye symptom may have a different cause, and a corticosteroid medicine, for example, can worsen a corneal ulcer.

Why does conjunctivitis return despite treatment?

Concurrent herpesvirus, ongoing mechanical irritation or another eye disease may be responsible. Re-examination helps find the cause instead of automatically restarting the same medicine.

This article is for general information only and is not a guide to treatment. If you notice the first signs of illness, contact your vet.

Paw4care editorial team

Sources

Guideline for Feline Respiratory Mycoplasma Infections, European Advisory Board on Cat Diseases, accessed 2026-11-03.
Conjunctivitis, Cornell Feline Health Centre, accessed 2026-11-03.
Conjunctivitis in Cats, VCA Animal Hospitals, accessed 2026-11-03.
Feline Respiratory Disease Complex, Merck Veterinary Manual, accessed 2026-11-03.
Guideline for Feline Herpesvirus Infection, European Advisory Board on Cat Diseases, accessed 2026-11-03.
Corneal Ulcers in Cats, VCA Animal Hospitals, accessed 2026-11-03.
Applying Eye Drops to Cats, VCA Animal Hospitals, accessed 2026-11-03.
Eye ulcers (corneal ulcers) in cats, PDSA, accessed 2026-11-03.

Mycoplasma conjunctivitis in cats: symptoms and treatment