Phylogenetic Diversity of Vibrio cholerae Associated with Endemic Cholera in Mexico from 1991 to 2008

Abstract

An outbreak of cholera occurred in 1991 in Mexico, where it had not been reported for more than a century and is now endemic. Vibrio cholerae O1 prototype El Tor and classical strains coexist with altered El Tor strains (1991 to 1997). Nontoxigenic (CTX−) V. cholerae El Tor dominated toxigenic (CTX+) strains (2001 to 2003), but V. cholerae CTX+ variant El Tor was isolated during 2004 to 2008, outcompeting CTX− V. cholerae. Genomes of six Mexican V. cholerae O1 strains isolated during 1991 to 2008 were sequenced and compared with both contemporary and archived strains of V. cholerae. Three were CTX+ El Tor, two were CTX− El Tor, and the remaining strain was a CTX+ classical isolate. Whole-genome sequence analysis showed the six isolates belonged to five distinct phylogenetic clades. One CTX− isolate is ancestral to the 6th and 7th pandemic CTX+ V. cholerae isolates. The other CTX− isolate joined with CTX− non-O1/O139 isolates from Haiti and seroconverted O1 isolates from Brazil and Amazonia. One CTX+ isolate was phylogenetically placed with the sixth pandemic classical clade and the V. cholerae O395 classical reference strain. Two CTX+ El Tor isolates possessing intact Vibrio seventh pandemic island II (VSP-II) are related to hybrid El Tor isolates from Mozambique and Bangladesh. The third CTX+ El Tor isolate contained West African-South American (WASA) recombination in VSP-II and showed relatedness to isolates from Peru and Brazil. Except for one isolate, all Mexican isolates lack SXT/R391 integrative conjugative elements (ICEs) and sensitivity to selected antibiotics, with one isolate resistant to streptomycin. No isolates were related to contemporary isolates from Asia, Africa, or Haiti, indicating phylogenetic diversity.

Sustained Local Diversity of Vibrio cholerae O1 Biotypes in a Previously Cholera-Free Country

“…The classical biotype responsible for previous pandemics has been increasingly rare, and it has not been isolated from Asia or Africa after 1992 (7). A recent series of retrospective studies have reported the discovery of classical, prototype El Tor, atypical El Tor, and nontoxigenic O1 strains with some unusual genetic features in Mexico from 1983 to 2008 (7–10). The latest of these studies, recently published in mBio , reports the comparative genomic and phylogenetic analysis of these various biotypes (8).…”

“…The article (8) describes a rare instance where a large variety of O1 strains are found to cohabitate outside of southern Asia. This diversity is remarkable because cholera was absent from Mexico for at least a hundred years until the 1991 Latin American epidemic.…”

“…This epidemic was mainly attributed to prototype El Tor and was proposed to have originated in Africa, because of similarity of Latin American isolates to African strains (5). The study presented in mBio (8) found a range of both prototype and atypical El Tor strains as early as 1991, some of which present no specific similarity to African strains. This casts serious doubt on the theory of a single African source origin for this epidemic.…”

“…The sampling of V. cholerae O1 performed in Mexico (8) is exceptional for an area where cholera has not been endemic for a long period of time. Isolates were collected from both clinical and environmental sources for more than 2 decades and carefully typed for all known characteristics of pandemic strains.…”

Isolation and identification ofVibriospecies in the Rio Bravo/Grande and water bodies from Reynosa, Tamaulipas

“…In Mexico in 1991, the first epidemiological outbreak by V. cholerae O1 was registered (Choi et al . ), and to date sporadic cases are still detected (SSA, ); also, in 2003–2004 the first epidemiological outbreak caused by V. parahaemolyticus was identified (Cabanillas‐Beltrán et al . ).…”