Molecular epidemiological approaches to study the epidemiology of tuberculosis in low-incidence settings receiving immigrants
Section snippets
Tuberculosis and migration
Tuberculosis (TB) is the most significant bacterial disease of humans worldwide. It is estimated that 50–100 million infections globally occur every year and approximately two billions people are infected with Mycobacterium tuberculosis. Although incidence rates of disease are falling globally and TB mortality rates fell by approximately 35% between 1990 and 2009, the current global burden of TB is still impressive. In 2009 there were 9.4 million new TB cases, including 1.1 million cases among
M. tuberculosis strain diversity and molecular typing methods
The discovery of polymorphic DNA in M. tuberculosis has led to a revolutionary advance in the field of TB epidemiology, as well as in the investigation of the evolutionary genetics of the tubercle bacillus. Based on distinct genomic polymorphisms, a number of molecular genotyping methods have been developed to differentiate, on a global scale, specific strains, strain families and evolutive lineages that constitute the M. tuberculosis complex. To date molecular epidemiologists benefit from
Molecular epidemiological studies on tuberculosis epidemiology in low-incidence settings
Different approaches and strategies, mainly based on the M. tuberculosis molecular typing methods resumed above, have been pursued by investigators to study TB epidemiology in low-incidence settings. The basic molecular approach consists in determining the composition of the M. tuberculosis strain population in the study area in order to distinguish between TB cases due to recent transmission and TB cases occurring by reactivation of a remote latent infection. This analysis entails precise
Conclusions
In low-incidence, industrialized western countries, the high incidence rate of TB among foreign-born persons and the risk of imports and transmission of potentially highly virulent M. tuberculosis strains, such as the Beijing strains, and/or the MDR/XDR strains, represent ongoing challenges for public health. Although a large part of molecular epidemiological studies agree that TB transmission between immigrants and the native population is generally low, certain studies express more concern on
Acknowledgment
This work was financially supported by the University of Pisa, Grant “Fondi di Ateneo, 2010”.
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2017, TuberculosisCitation Excerpt :The detection level quantified by Xpert assay was “low” and “very low” for 3 and 11 samples, respectively; this could be attributed to the paucibacillary load in the specimens due to uneven distribution of mycobacteria in tissue or to degradation of the DNA during the tissue fixation process [3,10]. No sample had evidence of rifampin resistance mutations, reflecting our local setting, that is a low-incidence country where drug resistance TB rate is relatively low [11]. Five of the 14 samples were culture-confirmed TB cases (data not shown); for the remaining 9 samples the corresponding tissue specimens were not available for TB culture.
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2016, TuberculosisCitation Excerpt :The molecular-epidemiological analysis of TB caused by M. tuberculosis Beijing strains in our setting confirms the high transmissibility of this family of strains, as shown by the high percentage of clustered isolates. Moreover, the relatively high proportion of Italian-born Beijing TB patients, often occurring in mixed clusters, supports the possibility of significant cross-transmission between foreign-born and autochthonous individuals, regardless of the fact that this event is generally considered epidemiologically irrelevant in low-incidence western countries receiving immigrants [29]. Apart from this reason of concern, high rates of extra-pulmonary localization and MDR occurrence, frequently reported for Beijing strains in other settings, were not observed in our survey; this confirms the existence of a substantial biogeographical heterogeneity affecting biological properties among the members that constitute the Beijing family.
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2014, Trends in ImmunologyIncreased genetic diversity of the Mycobacterium tuberculosis W-Beijing genotype that predominates in eastern China
2014, Infection, Genetics and EvolutionCitation Excerpt :The distribution of W-Beijing family strains in different geographical regions and their ability to predominate and spread in genotype clusters suggest that this group of strains may harbor a genetic advantage for infecting and causing disease in human populations (Bifani et al., 2002). Moreover, studies have shown that the predominance of W-Beijing family strains appears to have been driven by the modern human migration of the past few decades (Bifani et al., 2002; Garzelli and Rindi, 2012; Morcillo et al., 2005; Schurch et al., 2011). Latent infections and the complexity of clonal spread have limited the ability of traditional epidemiological methods to track the transmission of TB.