Pinkeye, or infectious bovine keratitis, rears its ugly head every summer. This summer seemed to be particularly bad. Classically, pinkeye is caused by the bacterium Moraxella bovis (M bovis). However, other organisms can be involved. Moraxella bovoculi, formerly known as Moraxella ovis, can be an offender as can Mycoplasma bovoculi and Mycoplasma bovis. IBR virus and occasionally Pasteurella multocida can cause a similar disease, as well. Cattle can be infected with more than one organism at the same time. Irritation of the conjunctiva due to dust or scratching, ultraviolet radiation from the sun and face flies can all play a role in the pathogenesis of pinkeye.
    Pastured animals are at significant risk, perhaps due to difficulty in controlling flies in pasture. We do see significant outbreaks in confined cattle, as well, even when fly control and manure management seem good. Because of the role of sunlight, face flies and dust, outbreaks are more common in the summer, but any of the organisms can cause infection at other times of the year.
    The source of the infection is usually other cattle. Infected animals can carry M bovis for over one year and may not show signs of pinkeye. M bovis organisms transmitted to other cattle by face flies or direct contact attach to the cornea with hair-like structure called pili. Within 12 hours of attachment, erosions start to form on the surface of the cornea. In early stages, most animals will have copious watery discharge from the eyes, may squint or close the lids, and are usually very sensitive to light. A small opaque area may form in a day or two in the center of the cornea. This is often when producers notice the disease. Most cattle owners are familiar with this stage and the later stages of pinkeye when more of the cornea becomes cloudy and a white scar eventually forms at the center of the eye.
    Fortunately a variety of antibiotics are often effective to treat M bovis. Cattle can be treated topically in the eye, with local injections or systemically. In some cases it may be necessary to treat the entire pen to attempt to reduce the number of carrier animals.
    Oxytetracycline is commonly used for systemic treatment since it is relatively inexpensive, available in formulations and has the characteristic of concentrating in the cornea at levels higher than found in blood or other body tissues. Mycoplasmas are harder to treat with antibiotics and may contribute to treatment failures.
    While treatment is often effective, a mass outbreak in multiple pens of heifers can be a real mess. Animals experience significant pain, may not eat well, and some are left partially or totally blind. Prevention and control are of utmost importance with this disease, but this is not always easy.
    There are several reasons for this. First, because apparently normal animals can carry the organism for over a year, there are plenty of reservoirs available for spread of disease to new victims in subsequent seasons. Second, we cannot control the weather or the amount of sunlight, so risk increases during summer. Sometimes controlling dust is difficult in warm seasons. Third, the potential mix of organisms involved can vary from farm to farm and year to year, so it can be hard to maintain control. Fourth, there are a variety of strains of M bovis, and even single strains can make changes to their structure that may affect the pathogenicity and ability of antibodies to attack the organism.
    The variety of causative organisms and the ability of M bovis to change are both reasons why pinkeye vaccines are often ineffective. These vaccines are fairly widely used today, but we often see severe disease in vaccinated animals. Veterinarians may choose to have autogenous vaccines produced from the specific strains and organisms isolated from a farm, but there is no guarantee the same organisms will be the offenders the next time, or that the M bovis will not modify itself to resist the effects of the vaccine.
    Thus, the best way to prevent and control pinkeye is to use a multi-pronged approach. First, control flies early and throughout the season. This means flies on all ages of cattle, young to mature. Fly tags are useful on pastured cattle. Premise sprays and pour-ons can help. Feeding larval inhibitors often are helpful. Second, try to use bedding that is not overly dusty. Sand bedding has successfully been used in hutches in the summer. Third, remove manure as is reasonably possible on a regular basis. Most fly species lay eggs in manure. Fourth, use vaccines appropriately at your veterinarian’s direction. Fifth, treat affected animals promptly. In some cases it may be wise to treat all the animals in a group to attempt to reduce the numbers of carriers early on in an outbreak. Pinkeye has been around for a long time. We are not likely to eradicate it anytime soon, but hopefully there are steps we can take to keep it under control.
    Jim Bennett is a dairy veterinarian at Northern Valley Dairy Production Medicine Center in Plainview, Minn. He and his wife, Pam, have four children. Jim can be reached at bennettnvac@gmail.com with comments or questions.