Pinkeye

Gerald Hauer, DVM
Bison Production Specialist
Alberta Agriculture, Food and Rural Development
Bison Centre of Excellence, Leduc, Alberta.
Phone: (780) 986-4100

Reprinted from The Tracker, December 1998

Summary

Pinkeye is a bacterial infection of the eye in bison, cattle and sometimes elk.  It can be mild and clear up on its own or it may be severe enough to cause blindness in the affected animal.  Treating pinkeye in bison is difficult so preventing the condition is the key to reducing losses.

Pinkeye

Pinkeye is an infection of the tissues of the eye of cattle, bison, and occasionally elk.  It affects both the cornea (clear outer covering of the eyeball) and the conjunctiva (the soft tissue that lines the inside of the eyelids).  It is not a fatal disease but it can have a great economic impact on a herd.  It causes temporary blindness, weight loss, decreased weight gain, scars on the eyes, decreased value of breeding stock, and in severe cases permanent loss of vision.   Bison were generally thought to be quite resistant to the condition but during this past summer many herds were affected to some degree.  Elk can also be affected but cases are rare.  This article will discuss the cause, typical appearance, treatment, and prevention.

Pinkeye is caused by a bacteria called Moraxella bovis.  The bacteria is present in the eye and nose of many healthy animals without causing a problem. This can serve as a source of infection for other animals in the herd or under the right conditions the bacteria can multiply causing a lesion.  There are a few different strains of the bacteria and each one has a different ability to cause disease.  Some strains cause mild lesions in a few animals while others are very contagious and cause a lot of problems in a herd.  This may partly explain why different herds were affected to different degrees this past summer.  Certain external factors may also explain some of the differences.  Conditions that make animals more likely to develop lesions include face flies that transmit the bacteria between animals, dry and dusty conditions that irritate the superficial structures of the eye, long grass that can scratch the cornea, high ultraviolet light, and other bacteria or viruses that cause secondary infections of the eye.  What is the reason that we saw so much of it this summer?  There may be a few reasons but the dry, dusty conditions that were prevalent in much of the province is likely the major contributing factor.

Pinkeye has a fairly typical appearance.  First, the eyes becomes very sore and the animal squints to avoid the bright sunlight.  Second, the eye begins to water profusely and wet patch develops below the eye.  Within a short time a white discharge is often noticed coming from the eye.  When the eye is examined there is cloudiness of the clear, outer surface of the eye (cornea) and often a white , raised spot develops in the center of the eye.  After a few days the cornea begins to turn pink or red as the eye attempts to heal itself by blood vessels growing in from the outer edges of the lesion thus the name “pinkeye”.  In severe cases the infection erodes the cornea completely and the eyeball ruptures leaving the animal permanently blind in that eye.  Usually one eye is affected but it can affect both eyes at the same time.

Sometimes the animal can fight off the infection on its own, however, the high cost of a permanently damaged eye and lost production makes treating the condition worthwhile.  The basic principles of treatment of pinkeye includes antibiotics to destroy the bacteria and a protective shield for the eye to ease the pain caused by light and dust.  There are many ways to accomplish this.  Most of my experience with pinkeye has been with beef cattle but the same principles can be applied to bison and elk.  To fight the infection ointments or sprays should ideally be instilled in the eye several times daily for a few days, but this is generally not a practical solution with these species.  Alternatively, the method that I use most frequently is to inject the upper eyelid with an antibiotics/antiinflammatory combination and apply some of the same solution directly on the eye, give the  animal an injection of long acting tetracycline, and then glue an eye patch over the eye.  Tetracyclines have been shown to reach high levels in the eye tissues and therefore are useful in the treatment of pinkeye.  The patch acts as a bandage to protect the eye.  By the time the patch rubs off in a few weeks, the eye has often healed.  A white scar may be left on the cornea but this does not usually cause a problem unless it is large and affects vision.   In severe cases where I feel that the cornea might rupture I apply antibiotic ointment and then suture the eyelid closed with an absorbable suture material.  It would be interesting to hear from some of the bison ranchers to see how they treated their pinkeye problems this past summer.  Send in your methods to the address below and I will include the responses in a future article in the Tracker.

Preventing pinkeye is a challenge.  Because of the different strains of the bacteria and the many contributing external factors it is hard to predict when a large problem will occur.  Vaccines are available to help minimize the disease.  Insecticide eartags to decrease the fly population have some beneficial effect.  In an outbreak, the whole herd is often treated with long acting tetracycline.  Again if you have any methods that you have used successfully to prevent the spread of pinkeye in your herd, let the rest of us know by sending me your technique.  You can reach me at 471-8884, fax me at 471-8770.

A short note about bacillary hemoglobinuria from an article a couple of months ago.  In the article I stated that I had not heard of any cases in bison but that they would probably be susceptible as well.  After the article came out one bison producer contacted me to say that he lost a bison to the disease and has heard of a few other ranchers with similar losses.  It appears that bacillary hemoglobinuria is also a concern in the bison herds as well.