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Infections with Brachyspira species in swine occur in most swine-rearing countries and can result in substantial economic losses. Of all swine-related Brachyspira species Infections, classical swine dysentery, caused by Brachyspira hyodysenteriae, results in the most severe clinical symptoms (eg, mucohaemorrhagic diarrhoea, weight loss, poor feed conversion). B hyodysenteriae was first recognised as the cause of swine dysentery in 1971 (Taylor and Alexander 1971). At that time, the strong haemolysis of B hyodysenteriae appeared indicative for pathogenicity since other, weakly haemolytic Brachyspira (formerly Serpulina, Serpula and Treponema) appeared to be commensal, and were therefore named Brachyspira innocens (Kinyon and Harris 1979). Several reports of clinical disease caused by weakly haemolytic Brachyspira indicated that not all weakly haemolytic Brachyspira species were non-pathogenic for pigs (Taylor and others 1980, Neef and others 1994). Further research of these weakly haemolytic isolates including DNA-DNA hybridisation, resulted in the designation of three more weakly haemolytic species, namely Brachyspira intermedia, Brachyspira murdochii and Brachyspira pilosicoli (Trott and others 1996, Stanton and others 1997).
These weakly haemolytic species of Brachyspira diverge in the severity of clinical symptoms they cause. B pilosicoli is pathogenic and causes spirochetal colitis in pigs, which is marked by non-haemorrhagic diarrhoea and a poor feed conversion. For B intermedia and B murdochii, the pathogenic potential is less clear-cut. Although both species have been isolated from clinical cases of diarrhoea, the clinical symptoms are mild or absent in experimental infections, and yet, high numbers of spirochetes are necessary to cause an effect (Jensen and others 2004, Jensen and others 2010).
Recently, a new type of Brachyspira infection has been described. Outbreaks of mucohaemorrhagic diarrhoea, caused by strongly haemolytic Brachyspira strains inconsistent with B hyodysenteriae, were reported in the USA and Canada. Phylogenetic analysis of these strains …