Pinkeye in Cattle

– Michelle Arnold, DVM (UK Ruminant Veterinarian)

Infectious Bovine Keratoconjunctivitis (IBK) or “Pinkeye” is a costly disease for the beef producer.  Preventing the disease is difficult because many factors are involved in the development of pinkeye including environment, season of the year, concurrent diseases, the strain of bacteria involved, and the animal’s genetic makeup and immune system.  Once pinkeye begins, it is highly contagious and can spread rapidly within the herd.  Careful attention to control of contributing factors and prompt, effective treatment in the face of an outbreak are necessary to reduce the spread and limit the damaging effects of the disease.

The cause of pinkeye is the bacteria Moraxella bovis (M. bovis) which is located in the eyes and nasal cavities of infected cattle.  A newly isolated strain of bacteria “Moraxella bovoculi” may play an important role as well but research has yet to confirm this.  M. bovis has two known factors that are important for causing pinkeye: pili and cytotoxin.  “Pili” are hairlike projections that enable M. bovis to stick to a damaged or injured surface of the eyeball (on the cornea).  There are 7 different serogroups of pili (A through G). “Cytotoxin” gives the bacteria the ability to kill corneal epithelial cells leading to an ulcer. It is also believed to be responsible for killing white blood cells needed to fight infection in the eye. The rupture of these white blood cells releases enzymes that further break down the cornea, making the ulcer even worse.  Cattle are the only known reservoir of Moraxella bovis and infected carrier animals may harbor this organism year round without showing any signs of eye problems.  Once pinkeye begins in a herd, it is highly contagious and can spread rapidly by direct contact through nasal and ocular discharges and by vectors such as flies.

Prevention of pinkeye is difficult because it is a complicated, multifaceted disease.  The best plan is to reduce or remove as many risk factors as possible that can result in damage to the cornea which allows the bacteria to take hold of the corneal surface. Many different combinations of contributing factors such as ultraviolet rays from the sun, face flies, excessive eye irritation, and stress may work together within a herd at one time.  Prevention is based on maximizing herd immune status, minimizing exposure to the bacteria, and maintaining as irritant-free environment as possible.

Steps to Preventing Pinkeye:

1.      Maximize Herd Immune Status- An overall good level of nutrition, adequate vitamin and trace mineral intake, a comprehensive vaccination program including the respiratory viral diseases IBR and BVD, parasite control, and basic biosecurity practices are all exceptionally important in improving the cow’s or calf’s ability to fight off any disease process (not just pinkeye).  There is no scientific evidence to support feeding excessive levels of any vitamin or mineral, including Vitamin A, will prevent diseases of the eye.  Biosecurity measures such as quarantine of new arrivals to the farm (including show animals) for three weeks before commingling with the herd are important in case any of these animals is carrying the disease.

2.      Maintain an irritant free environment- Any irritation to the eye allows Moraxella bovis to invade and cause pinkeye.   Prevent eye irritation with good face fly control, mow tall grass with seed heads, provide shade and clean water, and reduce sources of stress (such as overcrowding) if possible.  Control face flies with ear tags impregnated with insecticide and topically administered insecticides by way of back and face rubbers or dust bags they must walk under to get to water or mineral (see UK Extension Publication ENT-11:  Insect Control on Beef Cattle). Removal of fly breeding grounds and the use of certain feed additives will decrease the number of flies.  Provide shade to protect from the harmful UV rays of the sun.  Cool, clean drinking water (instead of stagnant pond water) is critical because intake is greater with clean water and this helps provide plenty of fluid in the eye, especially important in dry, dusty, and/or windy conditions. Tears are essential in eye defense mechanisms as tears wash away pathogens and tear proteins are an important part of protective mechanisms.  Do not forget to regularly check and clean automatic waterers.

3.      Minimize exposure to M. bovis [and M. bovoculi]- Early detection of animals with  the first clinical signs (tearing, squinting, and blinking) and then prompt, effective treatment are essential to reducing spread to herd mates and limiting damage to the eye. Long-acting antibiotics such as long-acting tetracycline or the prescription antibiotic tulathromycin (Draxxin®) are labeled for treatment of pinkeye.  Your veterinarian may prescribe the antibiotics florfenicol (Nuflor®) or ceftiofur (Excede®) to be used in an off-label manner for treatment as well.  Injectable antibiotics are generally the best option because of their long duration of activity and effectiveness in eliminating bacteria.  Topical sprays only remain in the eye a few minutes before tears wash them away so application is generally required 3-4 times daily to be effective. When severe ulceration exists, the eyeball may need extra protection with either a patch or the eyelids may need to be sutured (stitched) together.  Remember, preventing spread by treating affected animals is the single most important factor in controlling a disease outbreak.  Active cases of pinkeye with excessive tearing attract flies that widely spread the bacteria.  Topical application of a fly repellant to the face will also help reduce spread.

4.      Does vaccination work?  Immune responses to pili have been shown to be protective in some studies where animals are vaccinated with pili of a certain type and then challenged with a similar strain. This fact is likely responsible for why some herds might see a benefit from vaccination while other herds do not; if the vaccine strain stimulates immunity to a pilus type that is also present in the herd, there should be good protection.  In clinical trials, approximately half reported significant protection from commercial vaccines.  Therefore, it is unlikely that vaccination is the solution to all pinkeye problems although it may reduce the overall incidence of disease and severity of clinical signs.  When commercial vaccines are not effective, a vaccine can be made from bacteria cultured from pinkeye cases from one particular farm or farms in a certain area.  All cultures must be taken early in the course of disease; preferably when the eye is just beginning to tear excessively and before any medications are used.  These specialty vaccines can be effective if the “correct” M. bovis antigen is used.  However, autogenous vaccines often lose effectiveness within one to two years as the bacteria mutates and a new batch needs to be made from new cultures.

In summary, pinkeye is one of the most common diseases of cattle and is of major economic importance in Kentucky.  The keys to prevention and control of an outbreak are maximizing the herd’s immune status, minimizing exposure to Moraxella bacteria, and maintaining as irritant-free environment as possible.  Treatment decisions are influenced by numerous factors such as effectiveness of the drug, cost, labor availability, withholding times, facilities, and availability of a veterinary prescription.  Vaccines are not consistently effective in disease prevention and cannot be completely relied upon to prevent pinkeye.  The best strategy of treatment, prevention and control of pinkeye for a particular herd is best accomplished with the help of the local veterinarian.