The Seventh Pandemic Vibrio cholerae O1 El Tor Isolate in China Has Undergone Genetic Shifts

Abstract

Vibrio cholerae is the causative agent of the life-threatening diarrheal disease cholera (1). Seven distinct pandemics of cholera have been recorded since the first pandemic in 1817. The sixth pandemic, and presumably the earlier pandemics, were caused by V. cholerae O1 of the classical biotype. The current seventh pandemic, which originated in Indonesia in 1961, is the most extensive in geographic spread and duration, and the causative agent is V. cholerae O1 of the El Tor biotype. In 1992, an outbreak of O139 cholera emerged in the coastal areas of India and then spread to many countries in Asia (2, 3).The classification of the classical and El Tor biotypes of V. cholerae O1 is based on several phenotypic and genetic traits. The phenotypic traits include chicken erythrocyte agglutination (CCA), Voges-Proskauer (VP) test results, susceptibility to polymyxin B (PB; 50 units), and biotype-specific phages (1). The genetic traits include the variants of the gene encoding the cholera toxin subunit B (ctxB). In addition, the repeat sequence transcriptional regulator (rstR) gene and the major toxin coregulated pilus gene (tcpA) possess classical and El Tor-specific alleles, while the repeat in the toxin gene (rtxC) is present in El Tor but absent in classical biotype isolates (4).Several atypical or variant El Tor biotypes have recently been identified. The Matlab variant was the first atypical El Tor biotype. It was identified in Matlab, Bangladesh, between 1991 and 1994 (5). Another study (6) reported a hybrid CTX⌽ isolate carrying El Tor rstR and classical ctxB that has completely replaced the El Tor biotype in Kolkata, India, since 1995. Other atypical El Tor isolates have been reported in other countries in Asia (7,8) and Africa (9, 10), as well as in Mexico (11). Previously, we identified three novel El Tor variants from China in which the ctxB genotype was different from known genotypes (12). These results suggested that there were variants in China; however, the traits have not been investigated.In this study, 330 V. cholerae O1 El Tor biotype isolates were characterized and compared; these isolates were collected over nearly 50 years (1961 to 2010) and were obtained from different provinces in China from 1961to 2010, either from outbreaks or sporadic cases. All of the bacterial isolates were screened for the oxidase reaction and were identified by a slide agglutination test using specific polyvalent antisera against V. cholerae O1 (Ogawa and Inaba; S&A Reagents Lab, Bangkok, Thailand). The serogroups of these isolates were reconfirmed by real-time PCR targeting the O1 rfb-specific O biosynthetic gene (13).For phenotypic tests, polymyxin B (PB; 50 units) susceptibility test, CCA, and the VP reaction were performed using standard procedures (14) and a previous report (15). The V. cholerae reference classical isolate 569B and the reference El Tor isolate N16961 were included as controls. The phenotypic tests were repeated three times to ensure reliable results.To complement the phenotypic characterization of th...

A Molecular Surveillance Reveals the Prevalence of Vibrio cholerae O139 Isolates in China from 1993 to 2012

“…Furthermore, variant ctxB genotypes were found in O1 El Tor isolates in Haiti (37) and the O139 isolates during 1998 to 2005 in Bangladesh (38). Recently, we found that the ctxB-CL type of V. cholerae O1 El Tor appeared in 1992 and replaced the prototype El Tor from 2002 to 2010 in China (39), with other El Tor variants that differed from known ctxB genotypes also identified (40). Interestingly, we found no evidence of a shift to the ctxB-CL type among Chinese O139 isolates included in this study.…”

A review of perception and myth on causes of cholera infection in endemic areas of Nigeria

“…Within the contents of the abstract reviewed, no study so far has given a scientific proof on ambiguous religious belief, witchcraft and eating soil as causes of cholera infection). Scientific evidence have shown that the disease is highly contagious and one gets infected by faecal-oral transmission of toxin-producing serogroups (Marin et al, 2013;Oyedeji et al, 2013;Zhang et al, 2014). Irrespective of various opinions and perception on the causes of cholera epidemic, the fact remains that cholera is a water borne preventable and treatable disease, transmitted through ingestion of V. cholerae in contaminated food and water (Marin et al, 2013;Smith, 2002;Ghose, 2011;Farmer et al, 2003).…”

“…The world has experienced seven major pandemics of this disease since the early 19 th century (Faruque et al, 1998). The first six were caused by toxigenic strains of classical (CL) biotype, serogroup 01, which was reported to have originated from India, while the current 7 th is caused by V. cholerae 01 of the El Tor (ET) biotype (Zhang et al, 2014).…”

Combating Cholera

“…Serogroups are subclassified into two major biotypes. The first six pandemics of V. cholerae from the years 1817 to 1921 were caused by the classical biotype, whereas the seventh and current pandemic that started in 1961 was caused by the El Tor biotype 13 . Virtually all modern-day cholera is caused by El Tor, and environmental sampling identifies only El Tor, suggesting that classical biotypes are no longer prevalent.…”