Many cats have recurrent Conjunctivitis, sometimes associated with slight ‘Snuffly’ symptoms.

The Conjunctiva is the delicate membrane that covers the surface of the eyelids and the white part of the eye. When irritated, it becomes red and uncomfortable. The Cornea, or clear dome-like covering of the eye, can become involved in the inflammation – this is termed Keratitis, and causes the clear surface to become cloudy. This can lead to ulceration of the cornea, which untreated can damage the internal eye structures, or even lead to rupture of the eye.

The most common cause of conjunctivitis in cats is infection with the cat Herpesvirus (also called Rhino Tracheitis virus), and Chlamydophila Felis, a bacteria.

Calicivirus, another respiratory virus, Mycoplasma (similar to a bacteria) and other bacteria may also cause less severe conjunctivitis or may be present at the same time as Herpesvirus and/or Chlamydophila.


Respiratory infection is extremely common in young kittens, especially if they are facing other stresses (fleas, poor nutrition, cold etc). Respiratory infections are very contagious so common where cats are kept together: feral or stray kittens, shelter kittens and sometimes in pure-breed cattery kittens.

Herpesvirus infection typically also causes respiratory signs. This may be as simple as sneezing and watery eyes in a kitten that is well cared for. In other kittens, Herpesvirus can cause a severe nasal and chest infection. Eye discharge can gum the eyes closed, and untreated there can be damage to the cornea and internal eye. Intensive supportive care and medication is crucial for survival of these kittens.

Chlamydophila is also a common infection in kittens. The main symptom is a nasty conjunctivitis, and the Conjunctivae can become very red and swollen. This is very responsive to oral antibiotics. Some cats can be infected with both Herpesvirus and Chlamydophila, and other bacteria at the same time.


Swabs can be taken from the eyes to identify the cause of the conjunctivitis. This may be particularly useful in a cattery or shelter-wide problem, or for a cat that is not responding well. However, for most cats the vet will go by the symptoms and response to treatment.


As we have read, nearly all cats are exposed to Herpesvirus as kittens. Recovered cats can be what are termed ‘carrier’ cats – they are infected for life, but the virus lies dormant until the cat is stressed, when it can also pass the virus to other cats. This explains how a new cat in a household can suddenly come down with sneezing or eye inflammation.

70% of cats (some studies suggest >90%) are infected with Herpesvirus.

This also explains why a large percentage of conjunctivitis in adult cats is caused by Herpesvirus. In most cats, relapses are limited to watery nasal discharge and possibly sneezing. In other cats, relapses involve the eyes.

Herpesvirus flare-ups in the eyes are painful. Typical signs include squinting slightly in one or both eyes, eye discharge (usually brownish in colour), red conjunctivae, or all of these. This can progress to the cornea – herpetic keratitis – where the cornea looks cloudy, and is susceptible to ulceration. These ulcers come and go with stress, and require immediate veterinary attention. Recurring disease can also be caused by Chlamydophila.


Topical Treatment Eye antibiotics treat bacterial invaders, and lubricate and soothe the eyes, important in ulceration. Topical antivirals
are expensive, but may be valuable for some cats.

Oral Antibiotics These treat Chlamydophila infections very effectively, and will be prescribed for all animals in the family for at least a month.

Oral Interferon This is an immune system modulator that suppresses herpesvirus symptoms, and may be prescribed for some cats.

Oral Lysine The effectiveness of lysine, an amino acid available in most health food stores, is disputed by some vets, but it may be worth trying. Talk to your vet to see if they recommend lysine for your cat.

Eye Surgery Herpesvirus ulcers can be difficult to treat, and require frequent monitoring to ensure that they do not get worse. In some cases they will require surgery – under local anaesthetic to treat the cornea, or full surgery to apply a graft of conjunctiva onto the ulcer to seal and heal the defect in the cornea.


Herpesvirus and Calicivirus are included in routine cat vaccines, and Chlamydophila is included for at-risk pets.

Herpes vaccination does not prevent infection from feline herpes; what it does do is lead to less severe signs.

If healthy kittens are vaccinated by injection before they contact the virus, continued annual vaccination usually gives good protection. If the cat is then challenged by a particularly nasty strain of virus they usually develop only mild disease. Unfortunately, many kittens become exposed to viral strains before they are fully immunised. In catteries and shelters where the virus is prevalent this can be minimised by using intranasal vaccines, as these give protection at a much earlier age.

Cats with sore eyes