Infectious Keratoconjunctivitis in Animals
(Pinkeye, Infectious Ophthalmia)
Infectious keratoconjunctivitis of cattle, sheep, and goats is a common ocular condition characterized by blepharospasm, conjunctivitis, lacrimation, and varying degrees of corneal opacity and ulceration. In severe cases, ocular rupture leading to blindness can result. Affected animals can present at any age, but young stock are most commonly affected. The disease can occur at any time of year, but outbreaks are most often associated with warmer times of year, when risk factor exposure is greatest.
Risk factors for infectious bovine keratoconjunctivitis (IBK) include:
Although Moraxella bovis has long been considered to be the etiologic agent of IBK, other species of Moraxella, such as M bovoculi, M ovis, various Mycoplasma species (M bovis and M bovoculi), and infection with bovine herpesvirus type 1 and infectious bovine rhinotracheitis (IBR) virus may also play a role in disease.
Agents associated with naturally occurring conjunctivitis or keratoconjunctivitis in sheep and goats include:
Infectious keratoconjunctivitis usually is acute and tends to spread rapidly. One or both eyes may be affected. The earliest clinical signs are photophobia, blepharospasm, and epiphora; later, the ocular discharge may become mucopurulent. Conjunctivitis, with or without varying degrees of keratitis, is usually present. In sheep and goats, concurrent polyarthritis may be present in association with C pecorum infections. Appetite may be depressed because of ocular discomfort or visual disturbance that results in inability to locate food. The usual clinical course varies from a few days to several weeks. Most corneal ulcers in cattle with IBK heal without loss of vision; however, corneal rupture and permanent blindness can occur in the most severe cases.
Infectious keratoconjunctivitis lesions vary in severity. In cattle, one or more small ulcers typically develop near the center of the cornea. Initially, the cornea around the ulcer is clear, but within a few hours a faint haze appears that subsequently increases in opacity. Lesions may regress in the early stages or may continue to progress. After 48–72 hours in severe cases, the entire cornea may become opaque, blinding the animal in that eye. Blood vessels may invade the cornea from the limbus and move toward the ulcer at ~1 mm/day. Corneal opacity may result from edema (hazy white to blue corneas), which is a part of the inflammatory process, or leukocyte infiltration (milky white to yellow corneas), which indicates severe infection. Continued active ulceration may cause corneal rupture. Relapse may occur at any stage of recovery.
In all species, presumptive diagnosis of infectious keratoconjunctivitis is based on ocular signs and concurrent systemic disease. It is important to distinguish that the lesions are not due to foreign bodies such as plant awns or parasites (see Eyeworms of Large Animals). In infectious bovine rhinotracheitis, upper respiratory signs and conjunctivitis predominate, whereas keratitis accompanied by ulceration is rare. In bovine malignant catarrhal fever, respiratory signs are prominent with primary uveitis and associated keratitis. Microbial culture may help to confirm the causative organisms.
Diagnosis of classic bacterial agents such as Moraxella is often by aerobic culture of samples taken from affected eyes. Chlamydia and Mycoplasma spp require special media; the diagnostic laboratory should be consulted before sample collection. Cytologic evaluation of stained slides prepared from conjunctival scrapings of sheep and goats may reveal Chlamydia organisms; however, intracytoplasmic inclusion bodies can be difficult to recognize. PCR can be used to detect Chlamydia and Mycoplasma spp. Recent advances in molecular diagnostic tests may allow easier and faster identification of Moraxella species.
Good management practices are of paramount importance to reduce or prevent spread of infectious keratoconjunctivitis infection in cattle, sheep, and goats. Separation of infected animals is beneficial when possible. Gloves and protective clothing should be worn and then disinfected between animals when affected individuals are being handled. Temporary isolation and preventive treatment of animals newly introduced to the herd may be helpful, because some of these animals may be asymptomatic carriers. Ultraviolet radiation from sunlight may enhance disease (particularly in cattle); therefore, affected animals should be provided with shade. Dust bags or insecticide-impregnated ear tags can be used to reduce the number of face flies (Musca autumnalis), an important vector for Moraxella bovis.
For IBK, M bovis and M bovoculi commercial and autogenous bacterins are available; however, the efficacy of such vaccines against IBK has not been proven in randomized, controlled field trials. This lack of efficacy may arise due to antigenic variation between outbreak vs vaccine strains of Moraxella. Nevertheless, anecdotal evidence has suggested that, for some herds, M bovis and/or M bovoculi autogenous bacterins can be beneficial.
It is unlikely that any Moraxella spp vaccine will ever completely control IBK in the face of overwhelming challenge from and exposure to other risk factors such as flies, dust, other infectious agents, and trace mineral deficiencies. As such, planning and implementing a successful IBK control program should reduce exposure of cattle to the multiple risk factors associated with IBK.
Vaccinations are recommended at least 4–6 weeks before the annual anticipated first cases of IBK, to allow time for adequate immune responses to develop. The use of modified-live IBR vaccines has been associated with IBK in cattle, and consideration of the timing of IBR vaccination with animal shipment, especially in higher risk times of the year (summer/warmer months), may be important.
Moraxella spp are susceptible to many antibiotics. Because antibiotic susceptibility may vary in different geographic locations, susceptibility testing of isolated organisms is advised. In the USA, long-acting oxytetracycline (two injections of 20 mg/kg, IM or SC, at a 48- to 72-hour interval) and tulathromycin (2.5 mg/kg, SC, given once) are approved for IBK treatment in cattle. Other effective (but not FDA-approved) antibiotics include ceftiofur crystalline free acid (6.6 mg/kg, SC, at the base of the ear) and florfenicol (20 mg/kg, IM, two doses at a 2-day interval). According to current federal regulations in the USA, use of ceftiofur in cattle must follow approved bottle directions, including dose, route, and frequency.
Another common treatment for IBK is bulbar conjunctival injection with penicillin, but lack of a label indication for IBK/Moraxella may make other approved treatments more attractive.
For infectious keratitis in sheep and goats, topical oxytetracycline and antiseptic sprays are currently approved treatments. Topical applications should be applied at least three times a day to be effective, and thus are often not cost-effective or practical in herd settings.
A third-eyelid flap or partial tarsorrhaphy, which will shade the cornea from sunlight, together with subconjunctival injection, may reduce morbidity in severely affected animals. A temporary eye patch glued to the hair surrounding the eye is an inexpensive and easily applied treatment. The eye patch provides shade, prevents exposure to flies, and may help to decrease spread of organisms.
Animals with substantial uveitis secondary to keratoconjunctivitis that is particularly painful may benefit from topical ophthalmic application of 1% atropine ointment 1–3 times daily. This will prevent painful ciliary body spasms and reduce the likelihood of posterior synechia formation that occurs with miosis. Because of mydriasis caused by atropine, treated animals should be provided with shade. Systemic NSAID treatment (eg, flunixin meglumine) may also provide relief.
Early identification and treatment of pinkeye in cattle, sheep, and goats is important to minimize animal pain and suffering and to reduce spread within a herd.
Addressing risk factors is an important aspect of disease control.
For IBK in cattle, vaccination is controversial, but anecdotal reports suggest benefits.