Caseous lymphadenitis is a chronic, suppurative disease caused by Corynebacterium pseudotuberculosis. Sheep, goats, horses, cattle, and humans can be affected by this disease. Caseous lymphadenitis is currently of most interest in small ruminants and is implicated as the third leading cause of economic loss to the sheep industry in the western United States.1 In 1 report2 in which investigators examined samples from culled sheep from regions representing 9 western states, the prevalence was estimated as 42.41%. Although prevalence studies for goats in the United States are lacking, there is an everincreasing number of goats3 and caseous lymphadenitis should be an important health consideration.
The characteristic lesions of caseous lymphadenitis are single or multiple abscesses of the lymph nodes, skin, and viscera.4 The causative organism enters the body through broken or intact skin, via inhalation, or across mucous membranes. Inside the host, the organism spreads via the lymphatics to lymph nodes and internal organs, where abscesses develop during a period of 2 to 6 months. Bacteria are released into the environment through discharge from draining superficial abscesses or are aerosolized from ruptured abscesses in the lungs.5
Treatment and control modalities for caseous lymphadenitis include lancing of abscesses and flushing with potentiated iodine solutions, treatment with antimicrobials, culling of affected animals, surgical removal of abscesses, intralesional injection of formalin, and isolation from other animals to prevent disease spread.6 Lancing and flushing abscesses create a potential hazard for spread of purulent material to fomites and into the environment during the convalescent period. Although antibacterial protocols have been used for pharmacologic treatment of animals with caseous lymphadenitis,5,7 acceptable efficacy has not been determined because the abscesses typically are thickly encapsulated, which hinders penetration of antimicrobials.8 Additionally, because of the organism's intracellular location, some antimicrobials may not reach efficacious intracellular concentrations. At best, clinicians can hope for a reduction in size of the abscess and nonrecurrence of the condition. At worst, the abscesses can rupture and drain, which spreads organisms into the environment and could potentially infect others in the herd. Culling of genetically superior animals is often not a desirable or economically feasible option; however, retaining these animals in the herd greatly increases the risk of transmission. Although curative in the short term, surgical resection of abscesses does not address recurrence, requires local or general anesthesia, and is a more expensive option than the other reported treatment alternatives. Injection of formalin into the lesions reportedly is beneficial9; however, a carcass containing formalin would be considered adulterated and would be unfit for human consumption. The potential for negative public perception related to this practice is also a problem.
Tulathromycin, a newly introduced triamilide antimicrobial, is a member of a subclass of the macrolide family labeled for treatment of cattle and swine with undifferentiated respiratory tract disease. It is highly lipid soluble and, in cattle, maintains concentrations in lung tissue greater than the minimum inhibitory concentration (2.0 μg/mL) for the primary respiratory pathogens for at least 7 days.10 The longlasting properties and high degree of lipid solubility may allow this drug to enter encapsulated abscesses and achieve adequate intracellular concentrations.
The safety of tulathromycin used in an extralabel manner was investigated in another study11 conducted by our laboratory group. In that study,11 tulathromycin was administered at 25 mg/kg (11.4 mg/lb; 10 times the label dosage) to goats to investigate deleterious effects. No short-term adverse effects were detected in that study. To our knowledge, there have been no reported pharmacokinetic studies conducted in sheep or goats.
The objective of the study reported here was to compare the effectiveness of treatments for small ruminants with caseous lymphadenitis. Specifically, we evaluated the use of opening, flushing, and draining of lesions followed by penicillin administration, closedsystem lavage and intralesional administration of tulathromycin, and closed-system lavage and parenteral administration of tulathromycin.
Stoops SG, Renshaw HW, Thilsted JP. Ovine caseous lymphadenitis: disease prevalence, lesion distribution, and thoracic manifestations in a population of mature culled sheep from western United States. Am J Vet Res 1984;45:557–561.
USDA. Miscellaneous livestock and animal specialties—inventory and number sold: 2002 and 1997. Available at: www.nass.usda.gov/census/census02/volume1/us/st99_2_022_022.pdf. Accessed Jun 16, 2008.
Stanford K, Brogden KA, McClelland LA, et al. The incidence of caseous lymphadenitis in Alberta sheep and assessment of impact by vaccination with commercial and experimental vaccines. Can J Vet Res 1997;62:38–43.
Senturk S, Temizel M. Clinical efficacy of rifamycin SV combined with oxytetracycline in the treatment of caseous lymphadenitis in sheep. Vet Rec 2006;159:216–217.
Piontkowski MD, Shivvers DW. Evaluation of a commercially available vaccine against Corynebacterium pseudotuberculosis for use in sheep. J Am Vet Med Assoc 1998;212:1765–1768.
McKinzie D. Treatment of caseous lymphadenitis by intra-abscess formalin injection, in Proceedings. 3rd Small Rumin Med Semin Vet 1999;61.
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.
Washburn KE, Bissett W, Fajt V, et al. The safety of tulathromycin administration in goats. J Vet Pharmacol Ther 2007;30:267–270.
North Carolina State University, University of California-Davis, University of Florida. Food Animal Residue Avoidance Databank. Available at: www.farad.org. Accessed Aug 13, 2008.
Brown CC, Olander HJ, Zometa C, et al. Serodiagnosis of inapparent caseous lymphadenitis in goats and sheep, using the synergistic hemolysis-inhibition test. Am J Vet Res 1986;47:1461–1463.
BBL, BVA Inc, San Antonio, Tex.
API Corynebacterium identification system, BioMerieux Inc, Hazelwood, Mo.
Standard operating procedures, No. 0078, Texas Veterinary Medical Diagnostic Laboratory, College Station, Tex.
Epi Info, version 6.04, CDC, Atlanta, Ga.
SPSS for Windows, version 15.0, SPSS Inc, Chicago, Ill.
Case-Bac, Colorado Serum Co, Denver, Colo.