Abstract
Cholera is still a major public health concern in many African countries. In Angola, after a decade of absence, cholera reemerged in 1987, spreading throughout the country until 1996, with outbreaks recurring in a seasonal pattern. In 2006 Angola was hit by one of the most severe outbreaks of the last decade, with ca. 240,000 cases reported. We analyzed 21 clinical strains isolated between 1992 and 2006 from several provinces throughout the country: Benguela, Bengo, Luanda, Cuando Cubango, and Cabinda. We used two multiplex PCR assays to investigate discriminatory mobile genetic elements (MGE) [Integrative Conjugative Elements (ICEs), VSP-II, GI12, GI14, GI15, K, and TLC phages] and we compared the profiles obtained with those of different reference V. cholerae O1 variants (prototypical, altered, and hybrid), responsible for the ongoing 7th pandemic. We also tested the strains for the presence of specific VSP-II variants and for the presence of a genomic island (GI) (WASA-1), correlated with the transmission of seventh pandemic cholera from Africa to South America. Based on the presence/absence of the analyzed genetic elements, five novel profiles were detected in the epidemic strains circulating in the 1990s. The most frequent profiles, F and G, were characterized by the absence of ICEs and the three GIs tested, and the presence of GI WASA-1 and the WASA variant of the VSP-II island. Our results identified unexpected variability within the 1990s epidemic, showing different rearrangements in a dynamic part of the genome not present in the prototypical V. cholerae O1 N16961. Moreover the 2006 strains differed from the current pandemic V. cholerae O1 strain. Taken together, our results highlight the role of horizontal gene transfer (HGT) in diversifying the genetic background of V. cholerae within a single epidemic.
Highlights
Vibrio cholerae, the etiological agent of cholera, a gastrointestinal infection, has been responsible for seven known pandemics with the seventh pandemic currently occurring
We believe the strains presented in this study represent an important source of data depicting the presence of a variable population of V. cholerae O1 strains in the country
The epidemiology of V. cholerae O1 in Africa can be explained by multiple introductions of cholera from endemic regions of Asia, with the first introduction following the early dissemination of seventh pandemic in the 1970s (Kaper et al, 1995)
Summary
The etiological agent of cholera, a gastrointestinal infection, has been responsible for seven known pandemics with the seventh pandemic currently occurring. Over 200 distinct serogroups have been described, with only serogroups O1 and O139 associated with epidemic and pandemic cholera. V. cholerae serogroup O1 strains can be further classified in two biotypes, El Tor and Classical, based on differences in their phenotypic and genotypic traits (Kaper et al, 1995). During the seventh pandemic several epidemic lineages of V. cholerae O1 El Tor have emerged. Most notable was the emergence, in 1992, of a new epidemic serogroup in India and Bangladesh, named O139 or Bengal, which initially displaced the local existing O1 El Tor strains (Faruque et al, 2003). Molecular analyses demonstrated horizontal gene transfer (HGT) as the mechanism by which V. cholerae O1 strains acquired the O139 surface antigen resulting in a new epidemic serogroup (Bik et al, 1995)
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