Spirochetes are part of the normal flora of pigs, although Treponema hyodysenteriae
causes swine diarrhea. The colonization rate in human colon is variable and is influenced by many factors, including immune function, sexual practices, diet, sanitation, and community structure. The colonization rate of spirochetes in Europe is 2.5% to 9%; in the North of England, 1.5%; in Scotland, 6.9%[1,4]; in Washington, DC, 1.9%[1,4]; in Southern India, 64%; and in natives of West Africa, 100%. After World War I, the prevalence was 30% in Chicago, which was at least 10 times as high as that seen from 1975 to 1984. The prevalence in the homosexual population in the United States appears to be in the range of 28% to 36%.