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

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.

Molecular characterization of Mycobacterium bovis isolates from patients with tuberculosis in Baja California, Mexico.

The incidence of tuberculosis (TB) from Mycobacterium bovis in humans is likely to be underestimated and in some cases even ignored in most developing countries. This may be due to the difficulty of differentiating TB caused by either Mycobacteriumtuberculosis or M. bovis. Our objectives were to determine the prevalence of M. bovis human disease among the patients referred for study to the Tuberculosis Laboratory of the Tijuana General Hospital in Baja California, Mexico and to characterize molecularly the clinical isolates using 8 loci of MIRU-VNTR. A cross-sectional analysis of all culture-proven cases of tuberculosis was conducted during the period from January 1, 2011 through June 30, 2013. Clinical isolates that exhibited resistance to pyrazinamide (Z) were submitted for molecular analysis. A total of 2699 clinical samples were cultured during the study period and 600 (22%) that tested positive were processed for drug susceptibility for first line drugs. Sixty-four (10.7%) of the tested isolates tested were resistant to Z, and 27 (4.5%) of those were subsequently identified molecularly as M. bovis. Three of the M. bovis isolates were polyresistant to Z, isoniazid (H), ethambutol (E) and rifampicin (R) (Z+H+E, Z+E and Z+R); the rest were only resistant only to Z. VNTR typing, based on the 8 VNTR loci commonly tested for M.bovis, detected 12 allelic profiles (genotypes). The real burden of M. bovis cases among the total reported human tuberculosis cases can only be known from especially designed studies in which, during a specific period, all specimens submitted to tuberculosis diagnosis in one or more laboratories are cultured on the appropriate media and the isolated mycobacteria are analyzed to differentiate M. bovis from M. tuberculosis and other Mycobacterium species.