One Eye, Two Eye; Pinkeye, Blue Eye
by Carrie Bargren, DVM
Infectious Bovine Keratoconjunctivitis, commonly known as Pinkeye, is a multifactorial disease caused by a combination of infectious agents and environmental stimulants. The primary infectious agent is the bacteria Moraxella bovis, which has over 20 subtypes and all cause Pinkeye. Agents that contribute to the severity of disease and also serve as predisposing factors are Moraxella bovoculi, Mycoplasma spp., and Infectious Bovine Rhinotracheitis (IBR). However, the immune system of a healthy animal is able to prevent an eye infection until the eye is irritated by something in the environment. This makes the eye vulnerable to bacterial invasion and infection.
Face flies are a major source of eye irritation through mechanical means because they feed from the eye and nostril secretions of cattle. The surface of the eye can be scratched by tall plants on pasture and dust blown into the eyes can be incredibly irritating. The third form of irritation is not commonly thought of: UV rays from sunlight. Constant sun exposure without shade is very irritating to the eyes, especially in animals with white eyelids such as Herefords.
Face flies are also the main culprit for transmitting the disease within the herd. Animals that were previously infected can be silent carriers, showing no symptoms of infection, and shed M. bovis in eye and nasal secretions. The bacteria survive for 3 days on a face fly, so a fly feeding on multiple animals can transmit the disease to them all. Carrier animals will shed the bacteria for a long time, which is the main reason the bacteria survive the winter and cause a new outbreak the following year. Infections are more common in warm months due to the increased presence of eye irritants. Bacteria can be transmitted through direct contact between an uninfected eye and the eye/nasal secretions of a carrier or infected animal. Secretions can also be rubbed onto fencing, gates, feed bunks, etc. and picked up by an uninfected animal.
After transmission, it takes at least 2-3 days for symptoms to begin. Initially, the infected eye will be excessively watery and squinting. The conjunctiva (inner surface of the eyelid and white part of the eyeball) will become swollen and red while the cornea (transparent part of eyeball over the iris and pupil) remains clear. Within a few hours the cornea will develop a white haze which slowly intensifies until it’s completely opaque in 48-72 hours. A bluish tinge to the haze (corneal edema) indicates inflammatory cells brought in by blood vessels which will grow into the cornea 1mm/day. The vessels can add a pinkish hue to the eye, hence the name ‘Pinkeye.’ A milky white or yellow cornea indicates a severe infection and pus within the cornea. An ulcer forms in the center of the opaque cornea which looks like a small divot that will grow wider and deeper and is extremely painful. Left untreated, the ulcer will eventually perforate the cornea, rupturing the eyeball and resulting in permanent loss of vision. Loss of the eyeball is not common since cases are usually treated prior to this stage in disease. With timely treatment, the eye will fully recover in 3-5 weeks, although a few will retain a small white scar on the cornea.
Early treatment not only stops the active infection, but prevents bacterial shedding into secretions that would infect other animals in the herd. The vast majority of initial infections and even those with small ulcers respond well to long-acting tetracyclines like LA-200 at 4.5cc per 100 lbs under the skin in the neck, repeated in 48-72 hours. Non-steroidal anti-inflammatories (NSAID’s) like meloxicam or banamine will help control the pain and encourage feed intake during recovery. Advanced stages of infection with large ulcers may require an eye-patch or antibiotics injected directly into part of the eye which is best done by a veterinarian. There are antibiotic sprays and ointments, but they only work if applied 3-4 times daily until the cornea heals, which is usually not feasible. Additionally, keep in mind that most commercial ointments are either illegal to use in cattle or have extremely long withdrawal times.
As with any disease, prevention works better than treatment and for Pinkeye the best method is a combination of many. Fly control is essential, whether it’s in the form of fly tags, insecticidal pour-ons, back rubbers, dust bags, knock-down sprays or fly traps. Use multiple methods for the best control, but make sure to switch pesticide drug classes each year to avoid encouraging resistance amongst the flies. Use appropriate rotational grazing practices or clip pastures to reduce the potential for eye irritation from long plants. Lower overhead feeders and roll out round bales so that cattle can eat without sticking their entire head in and risk scratching their eyes. Proper bunk space reduces direct contact between infected and uninfected animals. Ideally, separate cattle with active infections until lesions resolve. Ample shade and breeding for pigmented eyelids will help reduce irritation from UV light.
Proper vaccination is also important, but keep in mind that the commercial vaccines (Alpha7-MB1, Vision 20/20) don’t contain every strain of M. bovis, but they will provide some cross protection. Given that each outbreak in each herd will have a different combination of M. bovis strains present, commercial vaccines will have varying degrees of success in preventing infection, but they will definitely decrease the severity. A vaccine specific to the herd can be formulated based on eye cultures from infected animals, called an autogenous vaccine. It can be used in addition to the commercial vaccines if infections are not controlled well by the commercial products. There are currently no published data to support the efficacy of the autogenous vaccine, but it is widely supported by anecdotal evidence, including farms that RVVC works with closely. Cattle should be vaccinated at 4-6 months of age, with calf-hood vaccinations, and boostered yearly. These boosters can be timed with the season or given at a specific time in each cow’s lactation. Additionally, proper vaccination against IBR, which is included in the respiratory vaccines, reduces the chance of a respiratory infection contributing to a Pinkeye infection. However, during an outbreak of Pinkeye, do not vaccinate infected animals with a modified live vaccine, as it could increase the eye’s sensitivity toward infection. As a general rule, only healthy animals should be vaccinated, and Pinkeye is no exception.
With summer officially here and flies out in full force, talk with your veterinarian about your plans to prevent and control Pinkeye.
Welcome Dr. Erin Harris!!
Dr. Erin Harris joined River Valley Vet Clinic in June at our Reedsburg clinic after graduating from veterinary medical school at UW-Madison. She grew up in West Bend, WI and although wasn’t raised on a farm, she fell in love with cattle during an introductory agriculture course during undergrad at UW-Madison (Animal Science, Dairy Science). Since then she has milked at several dairies, assisted in dairy-related research and drove tractor for a custom harvest crew. Her initial interests were in reproductive physiology, but Dr. Harris was drawn to veterinary medicine by the role veterinarians play in applying research to the real world to improve both animal and human health. Dr. Harris will be splitting her time between large and small animals at the clinic and her interests lie in reproductive medicine, soft tissue surgery and ophthalmology. Please stop by the clinic and introduce yourself or look for her on the road on her way to a call!
Sauk County Fair
RVVC would like to wish all participants of the Sauk County Fair the best of luck! As a reminder, here is a summary of requirements for animals from Wisconsin going to the fair. For more details, see the Sauk County Fair Book.
- Cattle – no testing or health paper requirements
- Swine – intrastate health paper with proper animal ID
- Sheep/goats – proper animal ID if intact, or not intact but over 12 months of age
- Horses – a current, negative Coggins form
- Camelids – no testing or health paper requirements
- Poultry/waterfowl – specific NPIP certificate or DTCAP-issued certificate. Contact RVVC or see Fair Book for details
- Small animals – dogs require certificate of rabies vaccination if over 5 months of age