Molecular Epidemiology of Cholera

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Abstract
This chapter describes the newer molecular subtyping approaches as they have evolved and been applied to investigations of cholera since the 1970s. It presents specific applications of subtyping in outbreak and epidemic settings and in retrospective studies of well-defined culture collections of Vibrio cholerae O1, including some preliminary information on the serogroup O139. The increasing knowledge of the molecular epidemiology of cholera has been stimulated by advances in technology and by unexpected occurrences of the disease from 1978 to 1993. In this chapter, the authors look at epidemiologically and phenotypically defined groups of V. cholerae isolates and discuss the use of their molecular genetic characteristics and relationships to address specific questions regarding the occurrence and spread of cholera, i.e., the molecular epidemiology of cholera. Robot-assisted DNA sequence analysis of a 460-bp polymerase chain reaction amplification product from ctxB indicated that classical biotype strains isolated from 1921 through 1970 had identical DNA sequences. The ctxB sequences of 45 V. cholerae O1 strains showed only three nucleotide differences among all strains, and there were three ctxB genotypes; the four classical biotype isolates belong to genotype. The multilocus enzyme electrophoresis (MEE) analysis of isolates indicated that both patient and food isolates belonged to the typical seventh-pandemic electrophoretic type (ET). Molecular subtyping of V. cholerae can identify specific outbreak strains and can often determine the geographic origins of strains.