Clinical efficacy of rifamycin Sv combined with oxytetracycline in the treatment of caseous lymphadenitis in sheep

Abstract

CASEOUS lymphadenitis (CLA) is a chronic disease of sheep and goats, characterised by the formation of suppurative abscesses in lymph nodes, caused by infection with the facultative anaerobe Corynebacterium pseudotuberculosis. Infection is transmitted in the discharges from ruptured lymph nodes of affected animals. The disease causes significant economic impact on the small ruminant industry through decreased meat yield, damaged wool and leather, decreased reproductive efficiency, culling of affected animals, and mortality due to the internal lesions (Blood and others 1989, Gilmour 1991, Williamson 2001). The clinical diagnosis depends on the presence of enlarged superficial lymph nodes and caseous, greenish pus; diagnosis is confirmed by the isolation and identification of C pseudotuberculosis (Blood and others 1989, Davis 1990, Williamson 2001). Rifamycin (3-4-methyl-1-piperazinyliminomethyl) is a clinically useful macrolide antibiotic produced by the Grampositive bacterium Amycolatopsis mediterranei. It is primarily used against Mycobacterium tuberculosis and Mycobacterium leprae, the causative agents of tuberculosis and leprosy, respectively (Lal and Lal 1994). Rifamycin SV has been shown to have in vitro activity against equine C pseudotuberculosis (Wilson and others 1988, Kohn and others 1993). However, it may cause hepatotoxicity and acute renal failure (Thornsbery and others 1983, Frank 1990, Molavi 1990, Plumb 1999), and thus it should be used with caution in patients with preexisting hepatic and renal dysfunction. There is no information about the adverse effects of the rifamycins in sheep. Resistance to the rifamycins can develop quickly, and the antibiotic is therefore most often used in combination with other antimicrobials (Thornsbery and others 1983, Davis 1990). This short communication describes a study of the efficacy of rifamycin SV, given in combination with a depot formulation of oxytetracycline, a broad-spectrum antibacterial agent with activity against a wide range of Gram-positive and Gram-negative bacteria, including obligate anaerobes (Barragry 1994), in sheep with naturally occurring CLA.