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The main cause of ovine footrot is the anaerobic bacterium Dichelobacter nodosus (Green and George 2008, Winter 2008, Kennan and others 2011). D nodosus is an obligate pathogen of sheep that does not survive long in the environment (Green and George 2008, Cederlof and others 2013), so the main reservoir of infection is in sheep. In theory, the organisms could be eliminated from a flock, through a combination of vaccination and/or antibacterial treatment (parenteral or topical) and/or culling of infected animals coupled with good biosecurity (Winter 2009). Elimination of footrot, using these methods, has been described in Australia (Egerton 1991, Abbott and Egerton 2003, Mills and others 2012) and Norway (Vatn and others 2012).
Gamithromycin is a macrolide antibiotic licensed for cattle in the treatment and control of bovine respiratory disease (Zactran, Merial, an injectable solution of 150 mg gamithromycin/ml). Though not currently licensed for use in sheep, gamithromycin has been used in the field in the control of footrot (Stamphoj 2011, Sargison 2012) and in treating an outbreak of lameness associated with Bacteroides melaninogenicus in sheep (Sargison and Scott 2011).
This paper describes attempts to eliminate D nodosus and footrot from one German and 48 Danish sheep farms through flock treatment with gamithromycin. In both countries, local veterinary authorities were consulted in order to obtain guidance and agreement for this off-label use (Strobel and others 2012).
In the German study, a flock of Merinolandschaf ewes was selected …