Infectious Keratoconjunctivitis in Animals

Infectious bovine keratoconjunctivitis

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Courtesy of Dr. John A. Angelos.

Infectious bovine keratoconjunctivitis, stained

Image

Courtesy of Dr. John A. Angelos.

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.

• Clinical signs and microbial culture

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.

• Improved management practices help prevent infectious keratoconjunctivitis

• In cattle, bacterins are also available for prevention

• Treatment includes antibiotics based on susceptibility of specific pathogens and supportive care

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.