Pinkeye, also known as infectious bovine keratoconjunctivitis (IBK) is a highly contagious disease, causing inflammation of the cornea (the clear outer layer) and conjunctiva (the pink membrane lining the eyelids) of the eye. Pinkeye results in a mild to severe infection and can cause blindness in approximately 2 percent of the cases. It has a major economic impact affecting cattle through decreased weight gain, decreased milk production, and treatment costs.
Pinkeye is a multifactor disease, which means there are many factors that predispose and contribute to the development of the disease. The primary infectious agent for pinkeye is the bacterium Moraxella bovis. This bacterium is found in the eyes of many recovered and apparently normal cattle.
Eye irritation is necessary for the development of the disease. This irritation can be caused by many risk factors including dust, pollen, weeds, UV sunlight, compromised immunity, and light skin around the eyes. These irritations may cause the eye to water and secrete mucus, which face flies feed upon.
Face flies feed around the eyes and nostrils of cattle, causing a mechanical irritation to the eye and spreading the disease from one animal to another. The bacteria can survive on flies for up to four days, so many animals may be infected by one fly. Other sources of irritation are tall weeds and grasses rubbing the eyes as cattle walk and graze, or feed and dust when cattle eat from feed bunks or the center of round bales. Dust on windy days, and exposure to excessive UV sunlight also increases the chances of disease development. Breeds which lack pigment on their eyelids are more susceptible to pinkeye because of their increased sensitivity to sunlight and decreased immune response in the eye.
As with many diseases, the disease outcomes can be influenced by nutritional imbalances, such as deficiencies of protein, energy, vitamins (especially vitamin A if the forage is lower quality), and minerals, (especially copper, selenium and zinc). The presence of other organisms such as the IBR virus, mycoplasma, Chlamydia, and Branhemella ovis will increase the incidence and severity of the disease.
Transmission occurs when a non-infected animal comes into contact with secretions infected with M. bovis. This may be direct contact, through face flies, or contact with an inanimate object that harbors the organism. Face flies are one of the primary vectors for spreading the bacteria and disease.
Management practices that reduce the risk factors associated with pinkeye are the most effective tools in decreasing the incidence of the disease.