Pinkeye
Pinkeye is a common, widespread and contagious bacterial eye disease of cattle caused by Moraxella bovis (M. bovis). It has a worldwide distribution. Although pinkeye is non-fatal, it has a marked economic impact on the cattle industry. Pinkeye rarely affects just one animal, but spreads throughout the herd. According to a 1993 study, costs resulting from decreased weight gain, weaning weight, milk production and treatment were estimated to be $150 million in the U.S. alone. Although newer figures have yet to be published, it is likely current losses greatly exceed this estimate.
Cause
M. bovis is the primary infectious agent initiating pinkeye in cattle. Other microorganisms capable of initiating similar clinical signs include bacteria Moraxella bovoculi and Mycoplasma spp., or viruses such as the Infectious Bovine Rhinotracheitis (IBR) virus, which can either add to the severity of the disease process or may serve as predisposing factors permitting a secondary infection with M. bovis.
The normal bovine eye has adequate defense mechanisms to prevent the growth of M. bovis. For the causative bacteria to invade the eye, there needs to be some underlying
irritation. Factors instrumental in causing eye irritation and allowing for invasion
of M. bovis and subsequent disease, are excessive ultraviolet (UV) light (sunlight); the face
fly (Musca autumnalis); and wind, plant material and dust. UV radiation or exposure to sunlight can sensitize
the eye, resulting in inflammation and increased likelihood of subsequent pinkeye
infection. UV light is especially a problem for white-faced cattle lacking pigmentation
around the eye. Flies not only serve as irritants as they feed on secretions from
the eye, but they also provide a means of transporting, thus transmitting M. bovis from infected to non-infected animals. Face flies can remain infected with M. bovis up to three days following feeding on infected material. Under experimental conditions,
disease transmission is uncommon without the presence of face flies, whereas it is
common when flies are present.
Cool and warm season grasses, hybrid Sudan grass and other forage sorghums, weeds
and brush produce air-borne irritants, pollen and chaff, as well as serve as mechanical
irritants. When animals eat out the middle of round bales, leaving a hay shelf over
their heads, the incidence of foreign body irritation is greatly increased. The same
situation occurs when hay is fed in overhead feeders. Foreign body irritation is especially
true with wheat hay or hay containing cheat grass.
Dust is more of a problem in confined feeding operations and is of minimal importance
compared to UV radiation, flies and plant material for grazing cattle.
Transmission
M. bovis, the bacteria commonly causing pinkeye is often carried by cattle showing no signs of disease. These animals have been previously exposed to the disease and recovered, but still maintain the organism in their nasal cavities and conjunctiva (inner surface of eyelids). These carrier animals become the source of infection for herd replacements and calves. Carriers allow the persistence of pinkeye in the herd and expose susceptible animals year after year. Once animals develop clinical signs of pinkeye, they also serve to infect other animals. Generally, most cattle will recover from pinkeye (with appropriate treatment).
Transmission of M. bovis occurs through direct contact, flies and inanimate objects. The organism is located
in the eyes and nasal cavities of infected cattle. Infected secretions from these
areas are a source of infection for other cattle. UV radiation, face flies, growing
plants and pollen production are at their peak in the summer and fall. These account
for the high incidence of pinkeye during this period. Stress associated with weaning,
increased stocking density (concentration of cattle), exposure to other infectious
agents (IBR virus, Mycoplasma spp., etc.) and hay feeding often are contributing factors to increased disease incidence
in late fall, winter and early spring.
Clinical Signs
Younger cattle are more susceptible to the disease because older animals have most likely developed acquired surface immunity (protective antibodies on the eye surface) as a result of previous exposure. The prevalence and severity of pinkeye on a particular site may vary from year to year and is dependent upon multiple factors. Infection rates can range from a few cases up to 80 percent of the herd at the peak of infection rate, usually the third or fourth week of an outbreak.
The incubation period is usually two days to three days, and in experimental trials
has extended to three weeks. Swelling and redness of the conjunctiva (inner surface
of eyelids and outer perimeter of eyeball), excessive tearing and squinting are the
initial clinical signs. Frequent blinking may be noticed by an astute stockman. Cattle
have a decreased appetite due to the excessive pain, and either no or mild to moderate
elevation of body temperature. A small opaque area may appear in the center of the
cornea in about two days, and by the sixth day, the entire cornea may have a gray-white
to yellow color with deep central ulceration of the cornea (Figure 1). Severe ulceration
and corneal rupture with loss of eye contents, cone-shaped bulging of the eye and
blindness are infrequent outcomes of pinkeye, but can occur from time to time. More
often, complete recovery occurs in three weeks to five weeks (with appropriate treatment),
with only a few affected eyes having a persistent white scar on the cornea. Large
corneal scar can contribute to partial blindness in the affected eye(s).
Figure 1. Pinkeye in a calf. Note the white halo surrounding the corneal ulcer (circle). The green color is due to positive uptake of fluorescein stain by the corneal ulcer.
Treatment and Management
Ideally, remove affected animals from the herd. Isolate and treat them according to your veterinarian’s recommendations. It may be a good idea to use an isolation pasture so affected animals do not expose their herd mates. Most cases of pinkeye are responsive to systemic antimicrobial treatment. Your veterinarian may recommend the use of additional antimicrobials administered topically (or under the conjunctiva), along with non-steroidal anti-inflammatory drugs (NSAIDs) to provide pain relief. This extra label usage of topical antibiotics and NSAIDs would require a prescription from your veterinarian. Milder cases may resolve without treatment with systemic or topical medications.
Affected animals benefit from protecting the eye from UV sunlight. Provide these animals
with shaded areas. Consider the use of eye patches, suturing eyelids or creating a
third eyelid flap. Consult your veterinarian for assistance in these methods to enhance
the healing process. Utilize fly control to reduce the annoyance of flies and reduce
the spread of pinkeye. Feed animals from the ground to reduce chaff and seed heads
from falling into the eyes. In confined feeding, manage the dust in the area to reduce
irritation to the eye.
Prevention
Like many diseases, management is often the most effective and economical method of disease control. When environmental conditions, animal nutrition and herd immunity are properly managed, animal health increases and disease frequency decreases. A decline in disease frequency results in a decrease in concentration of infective organisms on the premises; thus, a further decrease in disease frequency occurs.
Fly control – continues to be necessary due to isolated areas in Oklahoma having a significant
face fly population. Insecticide fly tags, sprays, charged backrubbers and dusts bags
are products that can provide chemical control. Use of feed through growth regulators
may help reduce the fly population. Manure management can be beneficial in controlling
stable and house flies in confinement operations. See Extension Fact Sheet VTMD-7000 Beef Cattle Ectoparasites.
Grass, weed and brush control – grazing management, mowing, brush mowing and spraying to minimize pollen and mechanical
irritation.
Hay and/or feed bunk management – lower overhead hay feeders, spread hay out, do not feed hay containing mature seed
heads or cheat grass in overhead feeders or round bales. Increase bunk space to decrease
direct contact.
Ultraviolet light (sun light) – breed for pigmentation around the eye, consider introducing Brahman influence into
the herd, provide shade or tree rows with ample room to prevent overcrowding
Disease management – isolate infected animals, and decrease environmental and nutritional distress.
Provide proper vaccinations as recommended by your veterinarian to improve overall
animal health.
Vaccination – commercial and autogenous pinkeye vaccines are available. Results reported by producers
and veterinarians have been mixed from their use of these products. Vaccines obtain
the best results when they are specific to the causative agent in the herd and administered
prior to infections. Culture, serotyping and sensitivity should be performed to determine
the bacterial pathogens and serotypes involved in the outbreak, providing information
about treatment and the choice of vaccines. Check with your local veterinarian about
the use of these products in a specific geographical area. It should also be emphasized
that vaccination is only part of a disease prevention program.
Maintain current health records – identify cattle that repeatedly become infected and those that seem more tolerant
to infection. This information can help with culling decisions.
Keys to Prevention
- Observe cattle carefully and identify the disease early for effective response to treatment (systemic antibiotic).
- Isolate new purchases.
- Isolate affected animals to reduce spread of disease.
- Consider what can be done to control environmental triggers for pinkeye.
- Consider the use of vaccines on the advice of your veterinarian.
- Maximize herd immune status through optimum nutrition; a proper vaccination program; and decrease the stresses of weaning, shipping and handling.
Melanie Boileau, DVM, MS, DACVIM
Associate Professor and Section Chief,
Food Animal Medicine and Surgery
Oklahoma State University Veterinary Medical Hospital
David Lalman, PhD
Extension Beef Cattle Specialist Oklahoma State University
Barry Whitworth DVM
Area Food/Animal Quality and Health Specialist
for Eastern Oklahoma
Oklahoma Cooperative Extension Service