Pinkeye often appears when dust, face flies and other eye irritations (bright sun, tall grass, viruses that damage the cornea, etc.) make conditions favorable for the bacteria (Moraxella bovis) to enter the eye. Face flies are the principle spreaders of the infection as they move from cow to cow, feeding on eye secretions. The disease is highly contagious; flies irritate the eyes, and physically carry bacteria from one animal to another.

In 1993, Kansas State University researchers using an electron microscope, found that face flies have sharp microscopic teeth.

Located on the end of the fly's tongue, the teeth irritate the eyes of cattle, making the eyes water. The fly feeds on the protein-rich secretions. The pinkeye bacteria gets into the eye by way of tiny wounds in the cornea resulting from the bites of the face fly.

The more cases of pinkeye in a herd, the more bacteria present to be transmitted to other cattle; pinkeye can spread rapidly when conditions are right. The face fly is the key factor; thus pinkeye is a summertime problem. You can have dust that irritates eyes, and have the bacteria present in the cattle, but without a mode of transmission, the likelihood of a significant pinkeye outbreak is greatly decreased, according to Korb Maxwell, DVM, beef industry specialist for Pfizer Animal Health.

Stockmen who detect signs of pinkeye and treat the first cases quickly can halt an outbreak by reducing the available bacteria that would otherwise be carried to susceptible animals by the flies. Control of face flies (as with insecticide ear tags) can also greatly reduce the incidence of pinkeye.

The disease goes through several stages after bacteria become established in the irritated eye. The eye waters and is held shut as it becomes sensitive to light. In another day or two, a white spot appears on the cornea and the eye may become cloudy. If the condition worsens, the spot enlarges and becomes ulcerated. The eye may heal in a few weeks (often leaving a small scar at the site of the ulcer). In serious cases, they eye won't heal without treatment; the ulceration grows larger and deeper, the cornea may protrude with pus and the eye may rupture, leaving the animal blind. Even if the eye doesn't rupture, damage and scars may cause partial or complete blindness after it finally heals. Most infected eyes heal within 60 days even without treatment, but damage from the infection usually leaves scarring on the cornea.

Cases of pinkeye treated in early stages respond very well to treatment, but even eyes that are badly ulcerated and temporarily blind will recover if the eye is not too damaged or ruptured. Two things are important in treating pinkeye: using an antibiotic to combat the infection, and protecting the eye from sunlight, dust, flies and further irritation while it heals.

Many commonly used antibiotics are effective against Moraxella bovis. Both injectable and topical treatments are available. Some veterinarians recommend injecting 1cc of penicillin combined with dexamethazone into the inside of the eyelid. The medication lasts longer at the site, providing antibiotic to combat the infection, and pain-killing anti-inflammatory relief. One treatment is usually sufficient if the infection is still in early stages, but in a severe case can be repeated in two or three days. This will usually clear up even a badly ulcerated, blind eye. An injection of long-acting oxytetracycline (such as LA-200) is also effective against pinkeye bacteria. ©