Intestinal spirochetosis is a disease of the large intestine seen in the absence of Brachyspira hyodysenteriae (see Swine Dysentery). This disease syndrome is being recognized more frequently worldwide.
The primary cause of intestinal spirochetosis is Brachyspira pilosicoli. Other weakly β-hemolytic Brachyspira associated with the condition are B intermedia and B murdochi. B innocens appears not to cause disease at all. B pilosicoli is emerging as a significant pathogen of people, especially in indigenous populations, homosexuals, and immunosuppressed patients. The organism is transmitted orally and survives extremely well in the environment. B pilosicoli has been isolated from a wide variety of animals, including waterbirds, rodents, and dogs. It has been shown to cause diarrheal disease in pigs, chickens, and people by experimental inoculation and in natural occurrence. The pathogenesis is not well studied, but apparently the end-on attachment of the spirochete to the mucosal surface interferes with the absorptive capacity of the colon, resulting in diarrhea.
Pigs initially have sticky feces on the perineum. The feces will appear as wet cement, and a mild diarrhea may result. Affected pigs may be inappetent and grow slowly.
The lesions in the large intestine are milder than those caused by B hyodysenteriae in swine dysentery. The volume of the large intestine may be increased and distended with thickening of the mucosa. In some pigs, a mucohemorrhagic colitis develops in association with enlarged mesenteric lymph nodes. Microscopically, spirochetes may be seen attached end-on to the mucosal surface and give the appearance of a false brush border. The mucosal surface has focal erosions with mild catarrhal exudate. Colonic crypts are often dilated, containing numerous spirochetes.
Important differential diagnoses include salmonellosis, proliferative enteritis, swine dysentery, and whipworm infection. B pilosicoli and other weakly β-hemolytic Brachyspira can be isolated on selective agar under anaerobic conditions. Biochemical tests and preferably PCR should be performed on Brachyspira isolates to confirm species identification.
Treatment and prevention of intestinal spirochetosis is similar to that of swine dysentery. Drugs such as tiamulin, lincomycin, and carbadox are effective. It is unknown whether the agent can be eradicated without total depopulation, as in swine dysentery, but because of the reservoir hosts and environmental survival it is doubtful.