Pinkeye, technically known as infectious bovine eeratoconjunctivitis, is a contagious and common eye problem in cattle.
Producers will initially notice the conjunctiva, the pink fleshy tissue surrounding the eye, is red and swollen. There will be a watery discharge from the eye and it may be partially closed. Usually only one eye is affected, but both may be showing signs.
The clear surface of the eye, the cornea, may become cloudy or silver-blue and a small white circular area may appear. As the disease progresses, the circular white area will enlarge and erode the surface of the cornea, creating a corneal ulcer. Discharge from the eye gradually decreases, but becomes thicker and whitish in colour.
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When the cornea becomes damaged, blood vessels may grow in from the edges of the eye in an attempt to heal the eye. In severe cases, infection may spread to the inside of the eye.
As the eye fills with white blood cells, it turns a light yellow colour. The infection may erode the cornea so the fluid inside may rupture through a hole in the cornea. If this happens, the eye will shrink and vision will be lost.
Signs of healing include regression of the blood vessels and a clearing of the cloudiness.
Occasionally, a permanent white scar is left at the site of ulceration, which would interfere with vision.
Pinkeye is unlikely to kill an affected animal, but weight loss and market discounts can be substantial.
The disease has traditionally been associated with the presence of the bacteria Moraxella bovis. This binds to its host’s eye by means of pili, fine microscopic hair-like structures. Once bound, it produces a toxin that attacks the cornea and the conjunctiva.
Some researchers consider the problem to be a syndrome, since many factors appear to play a role in the disease.
Any factor that compromises the integrity of the cornea may allow the M. bovis bacteria to gain a foothold. Corneal irritants such as dust, tall grass, seeds and barley awns can damage the corneal surface.
The problem seems to be most prevalent in summer. Ultraviolet light can damage the cornea and make the eye susceptible to invasion by M. bovis. Unpigmented eyelids are more susceptible to UV damage, and some breeds of cattle tend to be more prone to the disease.
Flies can irritate and mechanically injure the eye and can carry bacteria from animal to animal as they feed on the ocular and nasal secretions.
Younger animals seem to get the disease more often. Perhaps older animals acquire an immunity.
Animals with poor nutrition may have decreased resistance to infections. Crowding and direct contact with affected individuals will spread the disease more easily.
Combinations of these factors are likely responsible in an outbreak.
Research has shown that carrier animals who don’t necessarily show symptoms may be a significant source of infection.
Treatment depends on severity. It ranges from topical to injectable antibiotics, eye patches, anti-inflammatories, surgery and isolation of affected individuals.
These strategies are aimed at eliminating the M. bovis bacteria, reducing inflammation, preventing further irritation and decreasing the likelihood of spreading the disease to herd mates.
Long-term prevention focuses on reducing the factors causing eye irritation and increasing overall health of the herd.
Recent development of pinkeye vaccines may help to increase resistance of the eye to M. bovis infection.
Fly control, pasture management, a good herd-health strategy, adequate nutrition and prompt treatment of affected animals will reduce the incidence and severity of this common problem.
