One of the most common diseases among cattle during the summer months is pinkeye or ‘bovine infectious keratitis’. Many producers battle this disease every year even when preventative measures are taken. Thankfully, mortality with this disease is generally low or absent, however, morbidity may be as high as 80 percent. Economic losses are generally realized in treatment costs, reduced gains/milk production and reduced sale prices for animals with blindness or chronic lesions of the eye.
The primary pathogen associated with the disease is a bacteria called Moraxella bovis. Other pathogens have been identified as separate or contributing causes of pinkeye but Moraxella is responsible for the vast majority of cases in most herds. It has been shown that other non-infectious causes can also play a contributing role by causing additional irritation to the eye including flies, dust and solar radiation. These factors contribute to the disease process resulting in a more severe infection. The disease is thought to be transmitted primarily by the face fly.
Upon exposure, the bacteria adheres to the surface of the eye and establishes infection. Clinical signs of disease can be seen within a couple of days after initial infection has occurred. Generally, signs begin with watery eyes, photophobia and squinting due to discomfort. The disease progresses with ulceration of the surface of the eye, conjunctivitis and ocular discharge. Most of the time the disease is self-limiting and the infection is cleared and the eye healed in 3-6 weeks. Often times a small corneal scar is all that remains. Occasionally, the disease may progress to the point that the eye ruptures or the cornea is damaged such that the animal is left blind.
Several treatment options are available and can be expected to speed healing and reduce severity of the disease. Topical therapy with ophthalmic ointments is often effective but rarely practical for most cases because of the need for frequent administration. Subconjunctival injections of antibiotics or antibiotic/anti-inflammatory combinations has also been shown to be effective by providing therapeutic levels of the drug in the secretions of the eye for extended periods of time. Treatment with one or two injections of oxytetracycline (LA-200) has also been shown to be effective with less recurrence of symptoms when compared to subconjuctival injections.
Prevention is often the best treatment with any disease and for pinkeye, efforts should be directed primarily towards fly control. I recommend fly tags as a first line of defense. Pour-ons and backrubs can also help immensely in reducing fly numbers and subsequent transmission of the disease. Vaccination is recommended for herds that experience trouble with pinkeye, however, pinkeye vaccines are not as effective as many other commonly used vaccines, and they act only as an aid in the prevention of disease and do not provide complete protection. In severe outbreaks, mass treatment of the entire herd with antibiotics may help reduce additional cases.
Darren Loula, DVM, is a large animal veterinarian at Fair Grove Vet Service in Fair Grove, Mo.
