Brachyspira is a genus of bacteria classified within the phylum Spirochaetota

Brachyspira is a genus of bacteria classified within the phylum Spirochaetota.^{[2][3] [4]}

Brachyspira species include pathogens in pigs, birds, dogs, and humans.

B. pilosicoli colonizes millions of humans worldwide, leading to human intestinal spirochaetosis, a chronic, intermittent watery diarrhea vastly underdiagnosed ^[5] because of the lack of a simple diagnostic tool for clinicians. Multiplex qPCRs are promising diagnostic tools, as Brachyspira do not grow on conventional media.^[6]

B. pilosicoli also cause avian spirochetosis:^[2] birds might be considered as the natural reservoir.

B. hyodysenteriae leads to diarrheal disease in growing pigs worldwide, causing the so-called swine dysentery, typhlocolitis or porcine intestinal spirochaetosis, which contributes to major "production losses" in agrobusiness.

Some species like B. innocens or B. intermedia seem to be less virulent. 

 https://en.wikipedia.org/wiki/Brachyspira