Top 3 Causes of Conjunctivitis in Cats

What causes conjunctivitis in cats?

When it comes to causes of conjunctivitis, cats and dogs differ. With cats, viral and bacterial infections are the most common. For dogs, trauma and direct contamination are more likely to cause these signs.

Let’s discuss the causes of feline conjunctivitis in more detail…

Feline Herpes Virus (also called FHV-2 or Cat Flu)

Cats typically become infected with FHV-2 as young kittens, long before being rehomed. The kitten often shows additional signs such as sneezing, runny nose, and lethargy. But here’s the problem: the virus can look like it’s gone (and certainly the signs of flu, such as runny nose, will disappear) but the virus can stay with the cat in a latent (undetectable) state. It’s estimated that up to half of FHV infections result in latency. This is very similar to the human virus called Herpes Simplex Virus (HSV) which causes cold sores.

Under times of stress, or sometimes for no obvious reason, the virus can reappear - this time just as an eye infection. It may only cause conjunctivitis, or it could also infect the surface of the eye, causing an ulcer. These ulcers can have a typical “spider” pattern and can be detected by using a special stain called fluorescein.

Diagnosing FHV and differentiating it from other infectious causes can be challenging. A PCR test exists but this can be inaccurate, giving both false positive and false negative results. Some vets prefer to start trial treatment based on their “hunch,” and this is certainly a valid approach.

Treatment can include antiviral drops or tablets, as well as antibiotic eye ointment and anti-inflammatories.

Feline Herpes Virus is part of the core vaccines for cats. These are always recommended; however, they won’t remove FHV in its latent/dormant state.

To learn more, check out our related articles!

What You Need to Know About Vaccinating Your Cat

Upper Respiratory Infections in Cats

Feline Chlamydia

Chlamydia is another infectious agent that causes conjunctivitis in cats. Together, chlamydia and FHV account for over 75% of conjunctivitis in cats.

Feline chlamydia is caused by a small bacteria called Chlamydia felis. It sometimes behaves more like a virus and can lurk around in the eye without causing many signs of disease. Some cats can shed chlamydia without showing signs. These cats can act as reservoirs and re-infect the original patient, even after a course of treatment. For this reason, treatment is often recommended for all cats in the household, even if they appear unaffected.

Treatment can take the form of a tablet or eye ointment. Like FHV, a PCR test exists and is a helpful diagnostic tool, but it can be unreliable. For this reason, trial treatment is a valid option.

Other Causes of Conjunctivitis in Cats

Another common cause of conjunctivitis is trauma. Injuries to the eye can be caused by a fight with another cat or from general mischief, climbing trees, or hiding in bushes.

It’s important to ensure that your cat hasn’t scratched the surface of his eye. A complete eye exam, including fluorescein staining, is indicated when trauma is suspected.

Other causes of conjunctivitis include allergies, contamination from the environment, or immune-mediated diseases.

What should I do if my cat has conjunctivitis?

If you think your pet has conjunctivitis, it’s important to see a vet for an exam as soon as possible. Though it’s probably not an emergency, conjunctivitis can look like, or exist concurrently with many other more serious conditions (like an eye ulcer).

Read more:

A Vet’s Advice: Eye Exams and Eye Care for Your Pets

First Aid for Your Pet’s Eye

Eye Tests for Pets: Fluorescein Staining, Schirmer Tear Test, and Tonometry

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