Molecular Epidemiology

Molecular typing methods have been used to study the epidemiology of V. cholerae. While analyzing the nucleotide sequence of asd gene in V. cholerae, Karaolis et al.[8] demonstrated that the sixth and seventh pandemic strains and the U.S. Gulf coast V. cholerae O1 isolates may have derived from nontoxigenic strains, and postulated that horizontal gene transfer occurred in V. cholerae, resulting in the emergence of a new pathogenic strain. The use of gene probes to study restriction fragment length polymorphism (RFLP) in the ctxAB genes and their flanking DNA sequences, which are part of a larger genetic element (CTX element), indicated that the U.S. Gulf coast isolates of toxigenic V. cholerae O1 are clonal and different from other seventh pandemic isolates.[2- The diversity of CTX genotypes in V. cholerae O139 was reported, which may have resulted from the duplication of CTX prophage.[3] However, the toxigenic O139 strains prevalent in two endemic areas in India, including Calcutta and Alleppey, Southern India, and Bangladesh, are not clonal, and the Alleppey O139 strains are different from the Calcutta and Bangladesh strains, which contain the unique arrangement of the CTX prophage.[7]

Ribotyping and multilocus enzyme electrophoresis (MEE) analysis of the toxigenic V. cholerae O1 El Tor strains indicated clonal diversity, and the clones reflected broad geographical and epidemiological areas.[5,9,10] Comparative analysis of the El Tor strains of V. cholerae O1 and the epidemic O139 strains suggests that the O139 strains are related to El Tor strains and are derived from them by possible genetic changes in serotype-specific gene cluster.[3,9- Numerical analysis of ribotype patterns also revealed that V. cholerae strains belonging to the non-O1 and non-O139 serogroups are widely diverse from the O1 and O139 V. cholerae strains.[3,5,11- Further studies demonstrated the transient appearance and disappearance of more than six ribotypes of classical vibrios and three different ribotypes of V. cholerae O139. Different ribotypes often showed different CTX genotypes resulting from difference in the copy number of the CTX element and the variation in the integration site of the CTX

Swine Influenza

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