This condition is a bacterial infection of the surface of the eye (cornea) and the tissue surrounding the eyeball (conjunctiva) of the eye.

Cause

Pink eye is caused by the bacteria moraxella bovis. One of the main risk factors for development of pink eye is the grazing of rough pastures at times when fly numbers are at their highest. Flies alight around the eyes of infected animals and then fly on to the heads of neighbouring animals, thereby transferring the bacteria. In addition to vectors such as flies, moraxella bovis, which may exist in the nasal passages of carrier cattle, can be spread by direct contact between cattle, by aerosol spread and by fomites, eg feeding troughs. Development of pink eye is enhanced by damage to the surface of the eye by ultraviolet light from the sun, which lowers the resistance of the cornea to colonisation by Moraxella bovis. This is the reason that cattle with little or no pigmentation around the eyes and eyelids, eg Hereford cattle and their crosses, are most susceptible. Mechanical irritants may also play a role in predisposing to the disease, eg high dust or pollen counts and trauma from tall rough grasses.

Symptoms

The initial signs include excessive tear production from the affected eye(s), leading to staining of the side of the face. The affected eye becomes very light sensitive and so the animals tends to repetitively blink and hold the eye closed or semi-closed. The conjunctiva of the eye is usually reddened and, if left untreated, a grey opacity develops in the centre of the eye due to the build-up of fluid and cellular debris in the damaged cornea.

Pink eye can lead to severe damage to the front of the eye, with ulceration being so severe on occasions that rupture of the cornea occurs with loss of eye function.

Treatment

Pink eye is easily treated if detected in the early stages and results in a full recovery with no loss of vision. Topical antibacterial ointments can be very effective but they need to be applied two to three times daily. Moraxella bovis is sensitive to many antibiotics, eg cloxacillin, penicillin and oxyteyracycline. For advanced cases, your veterinary practitioner will be able to deliver a high concentration of antibiotic to the site of infection using a subconjunctival injection. In severe cases, injectable antibiotics, eg long-acting oxytetracycline, and anti-inflammatories prescribed by your veterinary surgeon are also warranted. If treatment is delayed, affected animals will be left with a permanent grey scar in the front of the eye which will impair vision to some degree.

Prevention and control

The best way to prevent pink eye is by reducing the impact of insect vectors like flies, and reducing the mechanical irritants in the environment, eg dust, rushes, long grass etc. Fly control measures should be initiated early in the season and include the use of insecticidal ear-tags, pyrethroid pour-ons and other similar products.