Elsevier

Infection, Genetics and Evolution

Volume 55, November 2017, Pages 378-383
Infection, Genetics and Evolution

Research paper
Molecular epidemiology of Mycobacterium tuberculosis in Baja California, Mexico: A result of human migration?

https://doi.org/10.1016/j.meegid.2016.07.001Get rights and content

Highlights

  • We describe the genetic diversity among 140 M. tuberculosis clinical isolates collected in Baja California, Mexico.

  • We identified nine different lineages.

  • A majority of lineages (41%) were grouped into three distinctive clusters.

  • Subset of isolates (12%) appeared to be autochthonous to Baja California.

  • We conclude that the molecular epidemiology of TB in Mexico is shaped by human migration.

Abstract

The State of Baja California (BC) exhibits the highest incidence and prevalence rates of tuberculosis (TB), and multidrug-resistant TB (MDR-TB) in Mexico. However information about the circulation of M. tuberculosis lineages in BC and Mexico as a whole is limited. Here, we describe the genetic relationship and genetic diversity among M. tuberculosis clinical isolates (n = 140) collected in BC between October 2009 and April 2011 with other regions of Mexico, the United States, and Latin America. All specimens were genotyped based on 24 mycobacterial interspersed repetitive units (MIRU)-variable number of tandem repeats (VNTR) loci. Population structure and minimum spanning tree (MST) analyses were used to assess the genetic diversity and distribution of BC isolates in comparison to USA and South America strains. Among the nine lineages observed, LAM, Haarlem and S were the most frequent identified in BC. Population structure analysis clustered most BC isolates (41%) into three distinctive groups that included strains from San Diego and South America, whereas other BC strains (22%) clustered with other Mexican strains. A subset of isolates (12%) seemed to be autochthonous of BC, while 25% were cosmopolitan and grouped into multiple clusters. It is highly likely that the TB genetic structure observed in BC is due to human migration.

Additional studies are required to determine the mechanism involved in the phylogeographic distribution of M. tuberculosis in Mexico. Implementation of domestic molecular TB surveillance programs is required to better understand the molecular epidemiology of TB not only in the region but at the national level.

Introduction

Tuberculosis (TB) is an infectious disease caused by mycobacteria belonging to the Mycobacterium tuberculosis complex (MTC). The World Health Organization estimated 9.4 million new TB cases and 1.5 million deaths attributed to TB in 2014 (http://www.who.int/tb/publications/global_report/en/). According to the Pan American Health Organization, in Mexico, the annual incidence of TB is ~ 16/100,000 habitants, and together with Brazil, Peru, Colombia, and Haiti, account for ~ 70% of all TB cases in Latin America (http://www.paho.org/hq/index.php?option=com_docman&task=doc_download&Itemid=270&gid=31283&lang=en). In 2013, the incidence of TB in Baja California was 54.4/100,000 population (pop), with a mortality of 5.7/100,000 pop, the highest in the country. In addition, BC reports the highest ratio of TB cases per capita of DR- and MDR-TB in Mexico (http://www.cenaprece.salud.gob.mx/programas/interior/micobacteriosis/descargas/pdf/SituacionActualTbMexico.pdf). BC shares one of the busiest borders in the world with the United States. Approximately, 30 million vehicles and 80 million individuals cross this boundary annually. This continuous transit across the border facilitates the concentrations of migrant populations from other Mexican states, Central and South America countries (http://www.cenaprece.salud.gob.mx/programas/interior/micobacteriosis/descargas/pdf/SituacionActualTbMexico.pdf). It is estimated that 45,000 legal migrants arrive to BC annually, from which 62% settle in BC (http://www.copladebc.gob.mx/publicaciones/2014/crecimientoPoblacional2014-2030.pdf). Several reports have shown that human migration is a key factor contributing to the spread of TB and increases the genetic diversity of M. tuberculosis (Borrell et al., 2010, Garfein et al., 2010, Svensson et al., 2011). In Mexico, limited information about the genetic diversity of M. tuberculosis is available (Lopez-Rocha et al., 2013, Martinez-Guarneros et al., 2013, Molina-Torres et al., 2010, Nava-Aguilera et al., 2011, Zenteno-Cuevas et al., 2015). Moreover, information about the impact of human migration on the molecular epidemiology of TB in Mexico is scarce. Thus, the aim of this study was to describe the genetic distribution of M. tuberculosis isolates from BC, Mexico and to establish the genetic relationship with isolates from other states in Mexico, USA and Latin America.

Section snippets

Study population

This is a cross-sectional study. Clinical isolates were collected between October 2009 and April 2011 from TB cases by the Tuberculosis Clinic and Laboratory, Tijuana General Hospital, Regional Reference Laboratory for suspicious DR-TB cases. Epidemiological and clinical information were obtained from medical records. All information collected was confidential and written consent was obtained from each patient. Institutional Review Board approval was obtained from the Ethics committee, General

Characteristics of population

Clinical isolates were collected from the Tuberculosis Clinic and Laboratory (TCL), Tijuana General Hospital, Regional Reference Laboratory. The TCL performs approximately 1000 microbiological cultures per year, of which 30–40% are positive. The TCL represents almost the 50% of all microbiological cultures for Mycobacterium sp. in Baja California.

In this study, 140 isolates were included, 100 (71%) and 40 (29%) were recovered from male and female individuals, respectively, giving a sex ratio of

Discussion

Here we have shown the relationship between M. tuberculosis isolates from BC with other isolates from Mexico, the United States and Latin America, which confirms a complex molecular pattern. A similar distribution of the LAM lineage has been previously reported (Martinez-Guarneros et al., 2013, Molina-Torres et al., 2010, Nava-Aguilera et al., 2011, Zenteno-Cuevas et al., 2015). Interestingly, the high frequency and distribution of the S lineage in BC contrast with previous reports in Mexico (

Competing interests

The authors declare that they have no competing interests.

Acknowledgements

This project was supported by the CONACyT grant No. 166624 “Epidemiología molecular de Mycobacterium tuberculosis en la frontera Noroeste México-Estados Unidos” and the CONACyT-Fondo problemas nacionales grant No. 213712.

The authors would like to thank Norma Martínez-Cisneros, Marco J. Nuñez-Bautista, Michelle J. Heredia-Gutiérrez and Andres Beltrán-Ureña for technical support.

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