Pinkeye in cattle, also known as Purulent Keratoconjunctivitis, is a disease which can be caused by a number of different bacteria. Infection is usually associated with physical irritants such as dust, wind, flies and stalky grass, which can damage the eye and/or transport bacteria into the eye. This is the reason that pinkeye is mainly seen in the summer months, even though it can occur at other times of the year as well. Infection is highly contagious.
The first sign of Pinkeye is the appearance of weepy eyes and sensitivity to light. This is a painful condition, so affected stock are often seen blinking a lot or keeping the eye partially/fully closed. It then progresses to ulceration of the cornea (surface of the eye) as bacteria literally dissolve the cornea, causing an ulcer. The appearance of the eye changes, and the surface colour becomes a pinkie cream colour (which gives the disease its name). When the ulcer becomes too deep, the inner layer of the cornea ruptures, fluid pressure in the eyeball is lost and the eye collapses.
Blindness due to Pinkeye may be partial or complete and temporary or permanent depending on the bacteria involved, the severity of the infection, and the level of treatment the animal receives.

Vaccination

Only one of the Pinkeye-causing bacteria, Moraxella bovis, has an effective vaccine. The vaccine is normally highly effective in reducing the spread of Moraxella. However, if the problem is caused by a different bacterium, the vaccination will not be effective at all. Almost half of the swabs taken by the Raglan clinic have Branhamella ovis isolated from them; this also is the cause of sheep pinkeye and vaccination isn’t protective. Branhamella ovis does however respond to antibiotic treatment. For this reason, it is recommended that eye swabs be taken to identify the cause before any large-scale treatment or vaccination is started. Once the cause is known, a decision can be made on whether or not vaccination is going to be effective.

If Moraxella has been found on a property in one year, it will often still be there in subsequent years. It can survive in carrier animals that show no signs, as well as on objects like the rails in yards. The usual procedure is to take swab samples and, depending on the severity of disease in individual animals, may include treatment with antibiotics at the same time. Vaccination will be recommended if Moraxella is isolated from the swabs, but only individual treatment with antibiotics is recommended if other bacteria are found.

Prevention

Vaccination can be used to slow an outbreak by reducing the number of animals affected, as well as by reducing the severity of the disease in infected animals. Also, if a property has had a proven Moraxella outbreak in a previous year, vaccinating all animals on the property before any infection has occurred may be recommended. This should ideally be given at least three weeks before the main risk period begins i.e. in late spring or early summer.
Isolating infected animals can help slow down the spread of disease, but since signs of Pinkeye can take time to develop, isolating animals before they spread the disease can be difficult. Minimising yarding of infected stock, particularly in dusty conditions, and not mixing infected and uninfected groups will also help reduce the spread. In hot weather ensuring paddocks have adequate shade so that there is less crowding of stock. Fly control will also help minimise spread of infection.

Treatment

Early treatment is really important- as soon as an animal is noticed with watery eyes. Treatment can be with antibiotics either directly into the eye or with injectable antibiotics. Generally, injectables are only used where direct treatment is not feasible due to factors such as lack of facilities. We often supply an antibiotic spray to use on the face around the eyes of all animals coming through the yards. This does seem to prevent excessive spread caused by the contact between animals at yarding. Minor cases of conjunctivitis not caused by Moraxella can spontaneously resolve without treatment, but pinkeye caused by Moraxella will always cause scarring of the eye and often the total loss of the eye if not treated.

Summary

If you suspect that you have Pinkeye on your farm, it is best to act fast. The consequences of Pinkeye can be severe, especially in terms of animal welfare. Not all outbreaks of Pinkeye are caused by the same bacteria, and the results of testing could change your treatment plan and/or future prevention plans. If you have questions regarding this article, or would like further information, please contact your Anexa Vet.