Phenotypic and molecular characterizations of Vibrio cholerae causing epidemics, 1991, and subsequent endemic cholera in Latin America

Burden

Beginning in Asia in 1961, the 7th cholera pandemic spread world-wide, reaching in Africa in 1970, and finally South America in 1991. A massive epidemic exploded in Peru in January 1991, spread rapidly from south to north of Latin America, and reached Mexico in June causing thousands of deaths. Since America was affected badly after about a century of no cholera, naturally the source of the disease was an enigma. Several studies in the past proposed contrasting views about the source, some arguing about a local source while others believed cholera to be an extension of 7th pandemic El Tor from Asia; although disease was rampant since 1991 and continuing throughout the continent causing morbidity and mortality in South and Central America.

Knowledge gap

A recent retrospective study on V. cholerae isolated from clinical and environmental sources in Mexico, between 1991 and 1997, confirmed both classical and El Tor biotypes with the latter presenting distinct genotypic and phenotypic traits including strains that had variants having a combination of classical biotype characteristics under the El Tor background. These results appeared in a sharp contrary to what has been proposed for the cholera in the Americas to be of Asian origin as El Tor was the only circulating biotype shown in Peru until recently. In order to further understand the evolutionary trends of bacteria causing endemic cholera in Mexico, we propose to carry out an extensive study on V. cholerae strains isolated from endemic cholera between 1998 and 2008. This study is vital for us to understand the evolutionary trend in terms of the prevalent sero-biotypes of V. cholerae to be able to develop a unified global model for intervention and preventive measures.
Relevance: Cholera is a pandemic disease claiming millions of lives globally. Efforts are being made to improve the understanding of cholera and V. cholerae associated with the disease globally. The America was affected badly after about a century of no cholera, and so very little is known about V. cholerae associated with the disease. The proposed study will generate important data on the phenotypic and genotypic traits of V. cholerae causing endemic cholera in Mexico during 1998 – 2008. The data obtained will help us to develop a unified global approach for intervention and preventive measure against cholera globally.

Hypothesis

After 1991 outbreaks in Latin America, cholera continues to be endemic in many countries of the Americas including Mexico. Our recent retrospective study on V. cholerae isolated between 1991 and 1997 showed the association of biotypes classical, El Tor, and El Tor variants with the endemic cholera in Mexico (Alam, et al., with H. Watanabe, M. Morita…A. Cravioto (JCM 2010). We hypothesis that the V. cholerae associated with endemic cholera is evolving independently in Mexico. The proposed follow-up study will generate important microbiological, molecular and phylogenetic data on V. cholerae causing endemic cholera in Mexico to be able to develop a unified global model for intervention and preventive measure against cholera globally.

Objectives

The aim of this study is to understand the latest status of cholera bacteria in Mexico, particularly to determine the prevalent sero-biotypes of V. cholerae and their clonal nature to develop a unified global approach for intervention and preventive measure against cholera world-wide.

Methods

V. cholerae isolated from endemic cholera in Mexico during 1998 – 2008 will be subjected to extensive phenotypic, molecular, and phylogenetic analysis. For this, we will involve serology, antimicrobial assay, multi-locus genome scanning (by simplex and multiplex PCR) and sequencing of targeted genes. DNA fingerprinting will be determined by molecular tools such as PFGE and the data will be analyzed by bionumeric software. Dendrograms will be generated by using appropriate computational tools.

Cholera is unheard of for a century from Latin America, and so is the V. cholerae. This sudy was designed to characterize V. cholerae associated with Latin American cholera in 1991 and subsequent years.

Better understanding of the phenotypic and gentypic characteristics will aid in deciding intervention and preventive measures against cholera.