Moraxella bovis is considered as the primary etiologic agent of IBK. Clinical signs associated with this contagious disease progressively include epiphora, blepharospasm, miosis, edema, corneal ulceration, descemetocele, and blindness.1 Economic losses attributable to IBK include reduced weight gains, treatment costs, and ocular disfigurement.1 In 1997, the USDA National Animal Health Monitoring System2 for beef cattle estimated that IBK was the most prevalent disease among breeding females and was the second most prevalent disease among calves > 3 weeks old. Environmental factors that augment the clinical effects of M bovis include UV light, wind, dust, pollens, ammonia, and face flies (Musca autumnalis).3
In some herds, 100% of all yearling calves may be affected by M bovis each year. The tendency of cases of IBK to be distributed over the entire summer combined with the lack of effective immunoprophylaxis increases the need for antimicrobials that can be used to effectively treat calves with minimum handling and expense. Treatment alternatives for IBK include subconjunctival and topical administration of penicillin4; IM administration of tetracycline5 and florfenicol6,7; and administration of tilmicosin, a macrolide, by various routes.8 Although subconjunctival administration of penicillin is considered as a common treatment for cattle with IBK, results of a controlled trial did not indicate efficacy.4 Additional chemotherapeutic agents would be useful because of the potential for antimicrobial resistance and the need for repetitive applications of some drugs. Repetitive treatments increase costs and enhance the risk of iatrogenic transmission of M bovis.
Tulathromycin is a semisynthetic macrolide that is chemically related to azithromycin. Tulathromycin is a member of the triamilide subclass of macrolide antimicrobials and is approved for use for treatment of cattle with bacterial pneumonia. Following a single SC administration (2.5 mg/kg [1.1 mg/lb]), tulathromycin reaches a peak plasma concentration of 414 ng/mL by 0.25 hours.9 The plasma half-life of tulathromycin is 92 hours.9 The drug is excreted through urine and feces in approximately equal amounts with apparent bioavailability of 91% after a single SC injection.9 At steady state, the drug has a volume of distribution of 11 L/kg.9 Although antimicrobial persistence in ocular tissue has not been studied, tulathromycin reaches lung concentrations as much as 325 times that of serum and persists at therapeutic concentrations for pulmonary pathogens for as long as 10 days. Results of a preliminary study using serial antimicrobial dilution assays indicated that the Tifton 1 strain of M bovis was susceptible to concentrations of tulathromycin > 0.5 mg/mL, which constitutes an achievable plasma concentration in parenterally treated calves. The long halflife and high bioavailability of tulathromycin, and the in vitro efficacy against M bovis, suggest that the drug may be a cost-effective treatment for IBK. The purpose of the study reported here was to determine whether a single injection of tulathromycin was effective in reducing healing times of corneal ulcers induced by M bovis in cattle.
Infectious bovine keratoconjunctivitis
Sylvania GS60, Osram Sylvania, Danvers, Mass.
NIH image, National Institute of Health, Bethesda, Md.
Dacron, Dupont, Kingston, NC.
SAS (PROC MIXED), SAS Institute Inc, Cary, NC.
SPSS, version 11, SPSS Inc, Chicago, Ill.
National Animal Health Monitoring System. USDA Animal and Plant Health Inspection Service Web site. Available at: www.aphis.usda.gov/vs/ceah/ncahs/nahms/. Accessed Oct 12, 2004.
Webber JJ, Selby LA. Risk factors related to the prevalence of infectious bovine keratoconjunctivitis. J Am Vet Med Assoc 1981;179:823–826.
Allen LJ, George LW, Willits NH. Effect of penicillin or penicillin and dexamethasone in cattle with infectious bovine keratoconjunctivitis. J Am Vet Med Assoc 1995;206:1200–1203.
Smith JA, George LW. Treatment of acute ocular Moraxella bovis infections in calves with a parenterally administered long-acting oxytetracycline formulation. Am J Vet Res 1985;46:804–807.
Angelos JA, Dueger EL, George LW, et al. Efficacy of florfenicol for treatment of naturally occurring infectious bovine keratoconjunctivitis. J Am Vet Med Assoc 2000;216:62–64.
Dueger EL, Angelos JA, Cosgrove S, et al. Efficacy of florfenicol in the treatment of experimentally induced infectious bovine keratoconjunctivitis. Am J Vet Res 1999;60:960–964.
Zielinski GC, Piscitelli HG, Perez-Monti H.. Efficacy of different dosages and routes of inoculation of tilmicosin in a natural outbreak of infectious bovine keratoconjunctivitis, in Proceedings. 32nd Annu Conv Am Assoc Bovine Pract 1999;32:261.
Nowakowski MA, Inskeep PB, Risk JE, et al. Pharmacokinetics and lung tissue concentrations of tulathromycin, a new triamilide antibiotic, in cattle. Vet Ther 2004;5:60–74.