Infectious Bovine Keratoconjunctivitis

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Infectious Bovine Keratoconjunctivitis (IBK)

Also known as

Pinkeye, New Forest Eye, blight

Description

Pinkeye is the common name for infectious bovine keratoconjunctivitis (IBK). This eye disease causes a lot of pain, which reduces the amount of time the animal spends grazing--resulting in poor weight gain, drop in milk production, etc. Severe cases may permanently damage the eye or rupture it, causing blindness.

Dealing with eye infections is complicated by the fact there are several causes of eye lesions that are often called pinkeye, creating signs similar to those of infectious pinkeye. Thus the success of treatment or vaccination can be varied.

Solid-colored cattle with dark skin around the eyes were traditionally thought to have less pinkeye, but this isn’t true. Though a white face (pink skin around the eye, with more irritation from ultraviolet light reflected into the eye rather than absorbed by darker skin) is a factor, there are many other factors involved; black-hided cattle also suffer from pinkeye.

Signs include runny eyes (excessive tears) and holding the eye shut to avoid bright light. These signs are usually seen 3 to 5 days after infection. At that point, small ulcers (white spots) may develop on the surface of the cornea and may enlarge to half-inch in diameter or more by 5 to 7 days and the eye may look cloudy.

Left untreated, some of these lesions become deep and may lead to permanent scarring and impaired vision, or eventually result in rupture of the cornea and blindness. The corneal lesions in some cases appear as soon as 10 to 12 hours after infection begins; some animals have full-blown pinkeye within 24 hours and it is urgent to treat the eye.

If the ulcer is due to trauma, such as a wound to the eye or a sticker stuck inside the lid, the ulcer will generally be off to one side of the cornea or near the edge, whereas an ulcer caused by pinkeye is usually in the center. Foreign material may be  under the eyelid, scraping the cornea every time the animal blinks. Common culprits are cheat grass seeds, microscopic slivers from burdock burrs or other plant material. These corneal injuries may start out as simple scrapes and then become infected with pinkeye bacteria.

Rupture of the eyeball is rare, but can occur with severe infection or following trauma when a blind animal runs into something. Otherwise, the eyes of most infected cattle heal within 60 days, leaving a scar (white spot) on the cornea.

Signs

  • Runny eye
  • Squinting
  • Avoidance of bright light
  • Small ulcer in center of cornea surface enlarging as the disease progresses
  • Cloudy eye

Causes

Moraxella bovis is the bacterium most commonly associated with pinkeye, but other organisms can be involved, including Moraxella bovoculi. Infection with other agents such as mycoplasmas and infectious bovine rhinotracheitis (IBR) can affect the eye and then cattle are more likely to get pinkeye.

Current thinking is that M. bovis is the primary pathogen and that M. bovicoli works as a co-pathogen. M. bovoculi is a very diverse bacterium with multiple virulence factors and we are continually discovering new things about it.

When researchers look at bacteria that cultured from affected eyes, and the difference between those two strains, reports show a high incidence of M. bovoculi in these cultures. We are not sure how those two pathogens work together.

Multiple factors play a role in this disease including interaction between the host, the pathogen and the environment--genetic susceptibility of the host, stress, comingling with other cattle (some of which may have pinkeye), environmental factors such as dust, UV light exposure, flies, mechanical irritation from rigid forage plants/grass awns, along with the pathogens.

There might be concurrent infections, and/or changing, mutating forms of the bacteria, new serotypes, shedding of bacteria from other animals in the group, etc. All these things overlap to increase incidence or severity of this disease.

In most cases, eye lesions result from spread of contaminated eye material from an infected eye to a non-infected animal, and this can happen in several ways. The disease is very contagious. It can be transmitted by nose-to nose contact, fluid from the eye, or rubbing the face on another animal.

Face flies carry it from animal to animal and irritate the eyes, making them more vulnerable.

Having Moraxella bovis in the eye isn’t enough to cause pinkeye in cattle. There must be trauma to the eye to enable bacteria to establish an infection. These bacteria tend to stay in the conjunctiva (delicate membrane that lines the eyelids and the exposed surface of the white of the eye), in the lubricating fluid. Unless there is trauma to the eye, the bacteria can’t bind to the cornea and cause the disease.

Things that cause trauma include high levels of ultraviolet light, infections by viruses and mycoplasma bacteria, plant pollens, tall grasses that scrape or cut the eye while the animal grazes, hay with sharp seed-heads, dusty feed, dusty or windy conditions, and face flies. As numbers of face flies increase, so does incidence of pinkeye.

The face fly has sharp microscopic teeth. Located on the end of the fly’s tongue, these teeth are used to irritate the eye, making it water.  This gives the fly access to the mainstay of its diet--protein-rich eye secretions.

Pinkeye bacteria can readily gain access to the eye, via the tiny wounds in the cornea caused by the face fly. The scrapes reduce some of the eye’s protective defenses. If flies scrape an infected eye and then move to another animal, they transmit the bacteria to the next animal.

Pinkeye incidence usually hits a peak in summer—with a lot of flies, long grass, dusty, and a lot of ultraviolet light. The conditions are perfect for trauma to occur to the eye.

Prevention

Incidence of pinkeye can be reduced by preventing situations where trauma occurs. Reduce the dust, clip the grass, provide shade, control flies, etc. but these practices are not always effective.

It’s difficult to control dust, almost impossible to control UV light, and on some properties it’s impossible to keep pastures clipped. There’s no one thing alone that is totally effective in prevention or treatment; it’s a multi-faceted approach--doing a number of things together to try to minimize the risk.

Fly control is a big part of pinkeye control, but it can be difficult to control face flies. Unlike horn flies that spend almost all their time on the animal, face flies don’t spend much time on cattle.

At any one time there may be only 5 to 10% of the face fly population on the cows; the rest of the flies are out in the pasture. And when they’re on cattle they don’t stay there long--just long enough to feed on eye secretions and go back to where they were. They are not exposed as much to a pesticide applied to the cattle (including fly tags in ears).

Some prevention methods may work on some farms and others won’t. On one farm the problem might be dust and the rancher institutes a fly control program, but it’s not the main cause of the eye trauma. On another farm it might be long grass.

Pinkeye is easily spread, so a person should be careful handling the animals. If you get cattle into the corral to treat some, and put them all through the chute, you create an environment in which all the calves are more susceptible. You may increase transmission through the herd, unless you bring the affected one in by itself to treat.

Some producers treat a few and the pinkeye outbreak gets worse. This could happen if you round up the herd, put them in a dusty corral and run all the calves through the chute; you might be making it possible for them all to get pinkeye.

Probably the most frequently used preventative practice is vaccination, to boost immune response to the causative organism, Moraxella bovis. Results with vaccination are variable, however because this is not the only bacterium that can cause pinkeye.

M. bovis binds to the eye by means of pili which are filament-like appendages of certain bacteria, containing some of the antigenic properties of the bacteria.

If a vaccine contains pilus antigens, it may be effective. But pilus antigens change more rapidly than vaccines can be changed. Most vaccines contain several pilus antigens. On a farm where M. bovis has that particular pilus antigen, it will probably work, but if the pilus antigens change, the vaccine may not work.

Trying to build good immunity in the eye is difficult. In many instances, vaccine won’t prevent an outbreak but may help by reducing severity of the cases and maybe shortening the time period the eye is affected.

In herds with severe eye problems that doesn’t respond to normal therapy, an option is to have your vet take swabs from eyes and try to culture the organism and determine what it is. Keeping good immunity to other diseases (such as IBR and BVD) can help prevent pinkeye.

Viral diseases can hinder the immune system and lead to higher incidence of other diseases including pinkeye.

IBR (infectious bovine rhinotracheitis, or “red nose”) can be mistaken for pinkeye because it can cause runny eyes and eye lesions that look like infectious pinkeye. Being a virus, IBR does not respond to antibiotic therapy. This is a herpes virus, and can cause ulcers.

Once the body is infected with herpes, it is always infected--like a person with recurring cold sores or shingles. Stress can bring it on again. IBR vaccines are effective at preventing some of the respiratory or reproductive problems associated with IBR, but not always effective at preventing the eye lesions

Total herd health is important, and this includes nutrition. There are many things involved in pinkeye outbreaks, such as trace mineral deficiencies.

Treatment

One aspect of prevention is treatment. If we treat each case early, before it becomes severe, we limit the impact of pinkeye on weaning weight and milk production--and may also save an eye that would otherwise be scarred or permanently damaged.

By treating an animal you may also keep the disease from spreading to other cattle. By treating early, you minimize spread of pinkeye (via face flies), from animal to animal.

Pinkeye caught in early stages responds well to treatment; even eyes that are badly ulcerated and blind can recover. Two things are important in treating pinkeye--using an antibiotic to combat the infection, and protecting the eye from dust, sunlight, flies and other irritants while it heals.

M. bovis is susceptible to many commonly used antibiotics, and some are marketed as topical treatments for pinkeye. It’s difficult to maintain adequate levels of drugs applied topically, however.

They don't stay in the eye long enough. Tears wash the medication out of the eye within a few hours. Ointments, powders, sprays or squirts must be repeated at least twice daily to be effective.

Normal cattle produce less than an ounce of tears daily. Cattle affected by pinkeye produce more tears, which rapidly wash away antibiotics applied to the surface of the eye. Certain antibiotics such as penicillin may be injected under the conjunctiva lining the inside of the eyelid, however.

This lasts longer at the site than topical medication and is sometimes mixed with a steroid to reduce pain and inflammation. Antibiotics given systemically are also helpful. LA-200 has been shown to be beneficial, injected intramuscularly or subcutaneously at a rate of 4.5 cc per 100 pounds of animal.

Antibiotics can resolve the disease quickly in early stages when the eye is simply irritated, watering and squinting—without much damage yet to the eyeball itself. The injectable antibiotics reach high levels in the tears when given systemically (into the muscle or under the skin). Tears bathe the eyeball with antibiotics.

If treatment is delayed and the eyeball ruptures, it can’t be saved, but eyes with deep ulcerations can heal, especially if you protect the eye. Some veterinarians suture the eyelids together, to keep the eye closed, and some pull the third eyelid across the eyeball and suture it there.

Either method will protect the eyeball from trauma, sunlight, dust, etc. Being covered helps the eye heal faster, keeping it from drying out, constantly bathed by its own tears. Eye patches are not quite as good as suturing the lids; patches don’t keep the eye closed, and may come off too soon.

Eyes generally heal faster (and with less complications) if protected with eye patches or sewing the eyelids shut. The latter has the advantage of keeping the eyelids immobile. There’s no blinking to rub the protruding ulcer and keep irritating the inflamed eye.

The eye is constantly bathed in its own tears, which seems to have a healing effect. Keeping it shut for awhile keeps it from drying out; many seriously affected eyes have a tendency to bulge, prolapse and become dried out, which is a detriment to healing.

Cases detected and treated early are less likely to develop complications (such as deep ulceration and scarring, “bubble eye” and permanent damage), but it is still important to treat eyes in late stages of pinkeye.

Not only will treatment help an eye heal faster and with less damage than if you let the disease run its course, but will also eliminate the bacteria causing the infection--so the animal does not continue to serve as a source of pinkeye for the rest of the herd.

About the Author

EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.

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