The genus
Brachyspira
includes nine officially recognised species, several of which are pathogenic to mammals and birds. B. pilosicoli, B. intermedia, and
B. alvinipulli
are the causative agents of avian intestinal spirochaetosis (AIS), a gastrointestinal disease in poultry caused by the colonisation of the caeca and/ or colo-rectum by
Brachyspira
. AIS primarily affects layer hens and broiler breeders over the age of 15 weeks. The severity of symptoms can vary but typically presents as reduced growth rates, delayed onset of lay, reduced egg production, faecally stained eggs, and diarrhoea. This disease is estimated to cost the UK laying industry £18 million per annum.
Brachyspira
colonisation in humans is common in populations from developing countries and HIV-positive patients; however, it is rarely investigated as a human pathogen.