Biodiversity of Mycobacterium tuberculosis in Bulgaria Related to Human Migrations or Ecological Adaptation

Abstract

Bulgaria is among the 18 high-priority countries of the WHO European Region with high rates of tuberculosis. The causative agent of tuberculosis is thought to have emerged in Africa 70,000 years ago, or during the Neolithic age, and colonized the world through human migrations. The established main lineages of tuberculosis correlate highly with geography. The goal of our study was to investigate the biodiversity of Mycobacteriumtuberculosis in Bulgaria in association with human migration history during the last 10 centuries. We analyzed spoligotypes and MIRU-VNTR genotyping data of 655 drug-sensitive and 385 multidrug-resistant M. tuberculosis strains collected in Bulgaria from 2008 to 2018. We assigned the genotype of all isolates using SITVITWEB and MIRU-VNTRplus databases and software. We investigated the major well-documented historical events of immigration to Bulgaria that occurred during the last millennium. Genetic profiles demonstrated that, with the exceptions of 3 strains of Mycobacterium bovis and 18 strains of Lineage 2 (W/Beijing spoligotype), only Lineage 4 (Euro-American) was widely diffused in Bulgaria. Analysis of well-documented immigrations of Roma from the Indian subcontinent during the 10th to the 12th centuries, Turkic peoples from Central Asia in the medieval centuries, and more recently Armenians, Russians, and Africans in the 20th century influenced the biodiversity of M. tuberculosis in Bulgaria but only with genotypes of sublineages within the L4. We hypothesize that these sublineages were more virulent, or that ecological adaptation of imported M. tuberculosis genotypes was the main driver contributing to the current genetic biodiversity of M. tuberculosis in Bulgaria. We also hypothesize that some yet unknown local environmental factors may have been decisive in the success of imported genotypes. The ecological factors leading to local genetic biodiversity in M. tuberculosis are multifactorial and have not yet been fully clarified. The coevolution of long-lasting pathogen hosts should be studied, taking into account environmental and ecological changes.

Keywords: adaptation; biogeography; genotype; history; immigration; tuberculosis.

Figure 1

Map of Bulgaria with 28 administrative districts: (A) prevalence of new and relapse TB cases (2018); (B) sampling sites and proportion of drug sensitive (in green) and multidrug-resistant (in red) MTBC strains. Circle size corresponds to sample size.

Figure 2

Ethnic maps of Bulgaria: (A) administrative districts and numbers of Turkish population; (B) administrative districts and numbers of Gypsy population.

Figure 3

Migration roads of Gypsy communities from the Indian subcontinent and Turkic peoples from Central Asia to Europe, and the prevalence of M. tuberculosis lineages L1-L4 on the map of modern states: (A) prevalence of L1; (B) prevalence of L2; (C) prevalence of L3; and (D) prevalence of L4.