Faecal excretion of intestinal spirochaetes by urban dogs, and their pathogenicity in a chick model of intestinal spirochaetosis

This study aimed to obtain information about the types of spirochaetes colonising urban dogs in Thailand, and to investigate their pathogenic potential in a day-old chick model of intestinal spirochaetosis. Spirochaetes were isolated from the faeces of six of 47 (12.8%) healthy dogs and 11 of 104 (10.6%) dogs with diarrhoea. Their biochemical properties and 16S ribosomal DNA sequences were analysed. Four isolates were identified as Brachyspira pilosicoli, three resembled “Brachyspira pulli”, nine clustered with “Brachyspira canis” and one was similar to Brachyspira intermedia. Canine isolates of B. pilosicoli, “B. canis” and “B. pulli”, and control strains of Brachyspira hyodysenteriae, B. pilosicoli and Brachyspira innocens colonised experimentally infected day-old chicks. The chicks did not develop diarrhoea, but were significantly lighter than the non-infected group and those infected with B. innocens after 21 days (P < 0.05). Using immunohistochemistry, spirochaetes were observed covering the surface epithelium and in the crypts of chicks in all three groups challenged with the canine isolates. Variable histopathological changes were seen, with the greatest inflammatory cell infiltration into the lamina propria occurring in the group infected with “B. pulli”. Canine “B. canis”, “B. pulli” and B. pilosicoli isolates may have pathogenic potential.