Cause: Intestinal spirochete (spiral bacteria) of the genus Treponaema.

Effects: Layers and breeders have wet faeces or diarrhoea, pasty vents, retarded growth, delayed onset of lay, dirty faecal-stained eggs, reduced egg weight, pale yolks. Turkeys and broilers show growth retardation, diarrhoea, pasted vent.

Avian intestinal spirochetosis (AIS) is a subacute to chronic nonsepticaemic disease characterised by spiral bacteria of the genus Spirochaetacae of which Treponaema, Borrlia and Serpulina are pathogenic to animals. The disease is caused by a heterogeneous group of spirochaetes in the rectum and/or colon.

One avian intestinal spirochaete, Serpulina hyodysenteriae, has been classified taxonomically. The remaining are unclassified but have morphological and biochemical features indicating placement in either the genus Serpulina or Treponaema. They have been shown to infect all domesticated poultry and wild birds. Intestinal spirochaetes of poultry are anaerobic gram negative, helix –shaped bacteria.

Initiation and severity of clinical disease is influenced by management, nutrition, environment and genetics. Contributing factors include moulting, onset of egg production, poor feed quality and floor housing. Light laying breeds are more susceptible.

Avian intestinal spirochaetes can be divided into three pathotypes, causing: subclinical infection; mild to moderate clinical disease or severe clinical disease. In layers, wet faeces, diarrhoea, pasted vents, retarded growth, delayed onset of lay, production of dirty faecal-stained eggshells, reduced egg weight and reduced egg carotenoid content may all be evident.

In turkeys, broilers and broiler breeders are similar to those in layers except that growth retardation is more severe.

Because spirochaetes can be normal flora or produce subclinical infections, characteristic clinical signs and lesions must be present in conjunction with visual demonstration of helical bacteria by dark-field or light microscopy for a presumptive diagnosis of AIS.

Confirmation of bacteria as spirochaetes should be through visualisation of distinctive ultra-structural features, demonstration of spirochaete antigens or by isolation in culture. Culture from fresh faecal droppings or caecal mucosa followed by further characterisation is necessary to confirm a diagnosis. In poultry, spirochaetes identified from faecal specimens should be distinguished from other spiral bacteria such as Campylobacter, Arcobacter, Helicobacter and Spirillum. In case of chronic diarrhoea or pasted vents, nutritional problems such as excess dietary salt, fats or soybean meal should be investigated. Other causes of chronic diarrhoea include enteric salmonellosis, colibaccillosis and coccidiosis.

AIS is chickens is a mild disease, but prevention is still more economical than treatment. Preventive measures include decreasing contact with faeces by raising birds off floors, frequent changing of litter or manure removal, good rodent and insect control programs, minimising dietary and moulting stress, provision of high quality feed ingredients and use of biosecurity measures.

For intestinal spirochaetes of commercial poultry, efficacy of chemotherapeutics varies between isolates. Use of 5-nitromidazole in water at a concentration of 120 ppm for 6 days is generally effective, although re-treatment after 4-8 weeks may be necessary. In some field cases, neomycin has produced clinical improvement.

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