In dogs, bacterial conjunctivitis is usually secondary to other underlying dysfunction e.g. poor eyelid anatomy, tear-film abnormalities etc. Most commonly isolated bacteria are Staphylococcus pseudintermedius; other organisms include Streptococci.

In cats, Chlamydophila felis is the organism isolated most often. Staphylococcus spp., Pastuerella multocida and Mycoplasma spp. are also isolated. Viral infection (herpesvirus, calicivirus) is an important cause.


The clinical signs of bacterial conjunctivitis are:
  • Red conjunctiva
  • Conjunctival chemosis (swelling)
  • Ocular discharge
  • Ocular discomfort


In dogs, the causes of conjunctivitis include:
  • Dust mites
  • Pollen
  • Mould
  • Dander
  • Cosmetics and perfumes
  • Drugs

In cats, there are several viruses that can cause conjunctivitis, one of the most common being the herpes virus. Cats that are regularly exposed to other cats with viral infections are more prone to develop the disease. In addition, allergies can cause the eyes to react as an external response to the allergen, or it may be as simple as a foreign particle lodging in the eye. Finally, pure bred cats are more likely to develop the disease than other cats.