Testing the efficacy of kitasamycin for use in the control and treatment of swine dysentery in experimentally infected pigs

Background: Swine dysentery (SD) caused by Brachyspira hyodysenteriae is an important disease in Australia. Aim: The aim of this study is to evaluate the macrolide antibiotic kitasamycin for use in SD control. Methods: The minimum inhibitory concentrations (MICs) of kitasamycin, tylosin and lincomycin for 32 Australian isolates of B. hyodysenteriae were evaluated. Mutations in the 23S rRNA gene were examined. Isolate ‘13’ with a low kitasamycin MIC was used to challenge weaner pigs. Sixty pigs were housed in 20 pens each containing three pigs: pigs in four pens received 2 kg/tonne of a product containing kitasamycin (3.1% active) prophylactically in their food starting 4 days before B. hyodysenteriae challenge (group 1); pigs in four pens were challenged and received the same dose therapeutically once one pig in a pen showed diarrhoea (group 2); four pens were challenged and received 4 kg/tonne of the product therapeutically (group 3); four pens were challenged but not medicated (group 4); two pens were unmedicated and unchallenged (group 5) and two pens received 2 kg/tonne and were unchallenged (group 6). Pigs were monitored for B. hyodysenteriae excretion and disease. Results: Macrolide resistance was widespread, and mutations in the 23S rRNA gene were identified in 23 isolates. Four isolates with kitasamycin MICs < 5 μg/mL were considered susceptible. Following experimental challenge, 10 of 12 unmedicated pigs developed SD. No pigs receiving kitasamycin prophylactical or therapeutically developed SD. Medicated pigs shed low numbers of B. hyodysenteriae in their faeces. Conclusions: Kitasamycin can help control SD in pigs infected with susceptible isolates of B. hyodysenteriae.