Infectious Keratoconjunctivitis in Cattle and Small Ruminants

Conventional treatment of IKC and IBK is to administer antimicrobials. Although Moraxella spp are relatively susceptible to a variety of antimicrobials, relatively few have a label claim for the treatment of IBK. However, anecdotal reports suggest the following treatment recommendations:

• In the US, parenterally administered oxytetracycline and tulathromycin have been approved for the treatment of IBK associated with Moraxella bovis in cattle.

• Topical oxytetracycline (formulated as oxytetracycline hydrochloride and polymyxin B sulfate in an ophthalmic ointment) is approved for pinkeye treatment in cattle and sheep.

• Dilute hypochlorous acid spray is also available in the US for treating pinkeye in cattle and goats.

• Topical ointments or sprays should be applied at least every 8–12 hours to be effective; thus they may not be practical in typical herd settings.

Other antimicrobials that have been experimentally shown as effective in treating IBK in cattle, but that are not currently FDA approved for this indication, include ceftiofur crystalline free acid and florfenicol. Federal regulations in the US prohibit extra-label use of certain drugs in food-producing animals. Extra-label use of cephalosporins (excluding cephapirin) is prohibited in cattle, swine, chickens, or turkeys for disease prevention; at unapproved routes of administration, doses, frequencies, or durations; or if the drug is not approved for that species and production class.

Given the lack of drugs specifically labeled for IKC treatment, extra-label use of drugs such as oxytetracycline and tulathromycin that are approved for the treatment of IBK in cattle is a rational antimicrobial treatment choice for IKC in small ruminants.

Injection of penicillin under the bulbar conjunctiva, though not specifically approved for treating IBK, is a common practice among cattle producers and veterinarians. Specific milk withdrawals following such use in dairy cattle must be observed to avoid illegal drug residues in milk.

Nitrofurazone-containing puffers are still available in farm supply stores for treating a variety of conditions, including eye infections in small animals. They may seem an attractive option for the treatment of IKC or IBK; however, the use of any nitrofurazone-containing product in food-producing animals is illegal in the US.

A temporary eye patch glued to the hair surrounding the eye is an inexpensive and easily applied treatment used in cattle with IBK. The eye patch provides shade, prevents exposure to flies, and may help to decrease the transmission of bacteria from infected eyes. In addition, in one study, corneal ulcers associated with IBK healed faster in cattle that received an eye patch along with systemic oxytetracycline and flunixin meglumine (1).

Animals with substantial uveitis secondary to keratoconjunctivitis may benefit from the application of 1% atropine ointment to the eye every 8–24 hours. This treatment prevents painful ciliary body spasm. Because atropine causes mydriasis, treated animals should be provided with shade. Systemic NSAID treatment (eg, with flunixin meglumine) may also provide relief.

Other possible treatments for keratoconjunctivitis, especially in animals with deep corneal ulcers, include the application of conjunctival or third-eyelid flaps, and tarsorrhaphy. These treatments can decrease morbidity in severely affected animals by providing corneal protection from light, flies, and physical irritants. In hospital settings where frequent drug treatments are more feasible than they are in the field, the administration of autologous serum eye drops can support the healing of an injured cornea.

The main focus of IBK prevention in cattle is to mitigate common risk factors known to be associated with IBK, as well as to vaccinate. Examples of risk factor control practices include the following:

• controlling external parasites to minimize face fly (Musca autumnalis, an important vector for Moraxella bovis) burdens via topical or parenteral treatments, dust bags, and/or application of insecticide-impregnated ear tags to calves

• mowing pastures that have mature or dry seed awns before turning animals out onto the pasture

• maintaining trace mineral supplementation programs (for copper and selenium supplementation in cattle raised in copper- and selenium-deficient areas)

For prevention of both IBK and IKC, it is recommended that affected animals be isolated from herdmates whenever possible and feasible. In addition, use of gloves and protective clothing that can be disinfected between animals, as well as disinfection of any handling equipment, is recommended to prevent the iatrogenic transmission of microorganisms potentially associated with these diseases.

The following solutions are commonly used for disinfecting equipment:

• ~0.05% chlorhexidine, made by mixing ~100 mL of a 2% stock solution per gallon of water.

• 10% household bleach, prepared by mixing ~1–1.5 cups of regular-strength household bleach per gallon of water. If the bleach is concentrated, ~0.5 cups of bleach should be used per gallon of water to achieve an ~10% solution.

Given that bleach is inactivated by organic debris, disinfecting solutions should be prepared more frequently when they become soiled.

In the US, no vaccines are commercially available for controlling IKC in small ruminants. Therefore, control of the disease relies primarily on 1) minimizing exposure by identifying, treating, and isolating sick animals; and 2) preventing transmission within a herd by temporarily isolating new herd additions and animals returning from shows or livestock exhibits.

For IBK prevention, Moraxella bovis and Moraxella bovoculi commercial and autogenous bacterins are available; however, the efficacy of these vaccines against IBK is a matter of considerable debate.

• In most published randomized, controlled field trials evaluating commercial or autogenous Moraxella bovis or Moraxella bovoculi bacterins that were parenterally administered, these vaccines were not found to be effective against IBK (2, 3, 4, 5).

  This lack of efficacy could arise from antigenic variation between outbreak and vaccinal strains of Moraxella. This possibility seems plausible, especially because of a report that two different genotypes of Moraxella bovis exist in North America (6). Two different genotypes of Moraxella bovoculi have also been characterized; however, only one of these has been associated with clinical cases of IBK (7, 8).

• In a study that evaluated three vaccines (an autogenous vaccine containing antigens from Moraxella bovis, Moraxella bovoculi, and Mycoplasma bovoculi; a commercially available Moraxella bovis vaccine; and a sham vaccine [adjuvant]), a numerically lower cumulative incidence of IBK was reported among animals that received the autogenous vaccine (9).

  Although this difference was not statistically significant, it may be biologically important, given that the animals in the autogenous vaccine group also had fewer cases of IBK that required retreatment.

• In contrast to the results observed in formal studies, anecdotal reports of successes for both commercial and autogenous vaccines against Moraxella spp suggest that in some herds, IBK prevention through vaccination can be effective.

  To allow time for adequate immune responses to develop after vaccination against IBK, vaccines should be administered ≥ 4 weeks before expected seasonal increases in IBK. The use of modified live virus vaccines against infectious bovine rhinotracheitis (IBR) has been associated with IBK in cattle; therefore, the timing of IBR vaccination with regard to animal shipment, especially at higher-risk times of the year (summer and warmer months), may be important (10).

Given that IBK occurs on a mucosal surface, intranasal vaccination to boost local ocular immunity to Moraxella spp antigens may provide an alternative to currently available parenterally administered vaccines. An experimental intranasal vaccine that used a Moraxella bovis cytotoxin subunit administered to cattle in two doses 21 days apart resulted in increased cytotoxin-specific tear IgA, as well as less severe corneal ulcers in vaccinates compared to controls (11).

It is likely that vaccines against Moraxella spp will never be completely effective at controlling IBK in the face of important risk factors such as flies, dust, other infectious agents, and trace mineral deficiencies. IBK control programs should aim to mitigate such risks as much as possible to help maximize the chances for success at preventing this disease in cattle.