Avian Intestinal Spirochaetosis (AIS) is a disease that affects commercial laying and meat breeding hens and results from the colonisation of the caeca and rectum by one or more species of anaerobic spirochaetal bacteria. AIS was first described in the 1990s in commercial chickens from the United Kingdom, The Netherlands and the United States. Seven species of the bacterium are capable of colonising poultry hosts, but only three are considered to be pathogenic. Of these, Brachyspira intermedia is considered the most common and significant species.

AIS is characterised by chronic diarrhoea in diseased birds, and subsequently results in faecal staining of eggs and wet litter. The resultant wet litter is an industrial problem and necessitates the mechanical cleaning of cages. A delay and (or) reduction of egg laying capacity is also observed, and hatched broiler chicks from eggs of infected parents show reduced performance compared to those of healthy parents. The significance of AIS is often unappreciated due to the variable clinical signs of the disease. In addition, the isolation of the bacterium can only be achieved using specialised media and techniques.


Currently there are no antimicrobial compounds that are registered for treatment of, or vaccines for prevention of , AIS. Compounds that are used to treat or prevent spirochaetosis in pigs have also been used in laying chickens with limited success, and importantly have not provided any long term control with recurrence of infection and reduction in performance occurring within 3 weeks to 3 months.

Research is currently in progress to develop a diagnostic immunological test method and a recombinant vaccine to detect antibodies and provide sufficient protection against AIS in chickens.