Infectious Keratoconjunctivitis: Introduction

Infectious Keratoconjunctivitis: Introduction
(Pinkeye, Infectious ophthalmia)

Infectious keratoconjunctivitis of cattle, sheep, and goats is characterized by blepharospasm, conjunctivitis, lacrimation, and varying degrees of corneal opacity and ulceration.

Infectious keratoconjunctivitis, cow

Infectious bovine keratoconjunctivitis

In cattle, Moraxella bovis with multiple serovars is the most commonly recognized cause of infectious keratoconjunctivitis. Most other ocular infections of cattle are characterized by conjunctivitis and minimal or absent keratitis. The primary differential diagnosis is infectious bovine rhinotracheitis (IBR), which causes severe conjunctivitis and edema of the cornea near the corneoscleral junction, but corneal ulceration is uncommon. Other organisms that may cause conjunctivitis of cattle, either alone or in conjunction with M bovis , include Mycoplasma spp and Neisseria spp . Infection with IBR or other microbes may increase the severity of infection with M bovis .

In sheep, infection with Chlamydophila ( Chlamydia ) pecorum is most common. Nonchlamydophilal infections may be caused by rickettsia-like organisms ( Colesiota conjunctivae ), Mycoplasma spp , and aerobic bacteria, notably Neisseria ovis . In goats, mycoplasmal infections are most common, although aerobic bacteria also have been isolated. Although much of the syndrome in young goats is caused by Mycoplasma agalactiae (see contagious agalactia, Contagious Agalactia and Other Mycoplasmal Mastitides of Small Ruminants: Introduction), it may be caused by other mycoplasmal species, notably M conjunctivae .

Clinical Findings:

The disease usually is acute and tends to spread rapidly. One or both eyes may be affected. In cattle, dry, dusty environmental conditions; shipping stress; bright sunlight; and irritants such as pollens, grasses, and flies tend to predispose to or exacerbate the disease. Flies also serve as vectors. In all species, young animals are affected most frequently, but animals of any age are susceptible. The initial signs are photophobia, blepharospasm, and epiphora; later, the ocular discharge may become mucopurulent. Conjunctivitis, with or without varying degrees of keratitis, is always present. In sheep and goats, concurrent polyarthritis may be present. In goats, mammary gland and uterine infection may also occur simultaneously with keratoconjunctivitis. Appetite may be depressed due to ocular discomfort or visual disturbance that results in inability to locate food. The clinical course varies from a few days to several weeks unless complicated by other diseases.

Lesions:

Lesions vary in severity. In cattle, 1 or more small ulcers occur near the center of the cornea (but occasionally near the limbus), often preceded by cloudiness of the central cornea. Initially, the cornea around the lesion is clear, but within a few hours a faint haze appears that subsequently becomes denser. Lesions may regress in the early stages or may continue to progress. After 48-72 hr in severe cases, the entire cornea may be 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. In sheep and goats, disease rarely advances beyond a mild corneal opacity, with the accompanying ulcer and conjunctivitis. Relapse may occur at any stage of recovery, but late lesions are not as severe as initial lesions.

Diagnosis:

In all species, presumptive diagnosis is based on ocular signs and concurrent systemic disease. It is important to distinguish that the lesions are not due to foreign bodies or parasites (see eyeworms of large animals, Eyeworms of Large Animals). In IBR, upper respiratory signs and conjunctivitis predominate, while keratitis accompanied by ulceration is rare. In bovine malignant catarrhal fever, respiratory signs are prominent with primary uveitis and associated keratitis. Microbial culture may be beneficial in confirming the causative organisms. Chlamydophila and Mycoplasma spp require special media; the diagnostic laboratory should be consulted prior to sample collection. Cytologic evaluation of stained slides prepared from conjunctival scrapings of sheep and goats may reveal Chlamydophila or Mycoplasma organisms. However, the intracytoplasmic inclusion bodies can be difficult to recognize. PCR analysis can be used to detect Chlamydophila and Mycoplasma spp .

Prevention and Treatment:

Good management practices are of paramount importance in reducing or preventing spread of infection in cattle, sheep, and goats. Separation of infected animals is beneficial when possible. 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 tags can be used to reduce the number of face flies ( Musca autumnalis ), an important vector for M bovis . M bovis bacterins are available and can be administered before the beginning of fly season. The efficacy of these bacterins is controversial. Although they are unlikely to prevent M bovis infections, immunization may reduce the severity and duration of infection in affected animals. IBR infection may predispose cattle to infection with M bovis ; thus, vaccination of herds against IBR may reduce outbreaks of M bovis . However, cattle should not be vaccinated during an outbreak with M bovis .

M bovis is susceptible to a variety of antibiotics. Because antibiotic susceptibility may vary in different geographic locations, bacterial culture and susceptibility testing is advised. Ampicillin, penicillin, gentamicin, and kanamycin can be injected subconjunctivally; best results are obtained with injection into the bulbar conjunctiva. Oxytetracycline is generally considered the drug of choice for systemic therapy because it is concentrated in corneal tissue. It cannot, however, be injected in the subconjunctiva because it will cause conjunctival necrosis. Two injections (20 mg/kg, IM) of a long-acting oxytetracycline formulation (200 mg/mL) at 72-hr intervals is the treatment of choice. Sulfonamides (eg, sulfadiazine and sulfamethazine) may also be effective when administered systemically because most of them pass readily into the tear film. Florfenicol (20 mg/kg, IM, 2 doses or 40 mg/kg, SC, 1 dose) and tilmicosin (10 mg/kg, IM, 1 dose) may also be used systemically. Systemic therapy can be augmented with topical applications of antibiotic, subconjunctival injection, or both. Topical applications of ophthalmic preparations should be applied at least tid to be effective, and thus are often not cost-effective or practical. Effective antibiotics for topical ophthalmic use include triple antibiotic, gentamicin, and a combination oxytetracycline/polymyxin B ointment. A third-eyelid flap or partial tarsorrhaphy, which will shade the cornea from sunlight, together with subconjunctival injection, may help 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 and prevents exposure to flies, decreasing spread of the organism.

For sheep and goats, in which chlamydophilal and mycoplasmal infections are most likely, respectively, topical tetracycline, oxytetracycline/polymyxin B, or erythromycin ointments are the treatments of choice. These preparations are all effective against Chlamydophila or Mycoplasma and should be applied 3-4 times daily. If topical therapy is not practical, an injection of long-acting oxytetracycline (10-20 mg/kg, IM) or the addition of oxytetracycline to the feed (80 mg/animal/day) may be beneficial.

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 may be used to provide relief from the secondary uveitis.