Towards the molecular epidemiology of Mycobacterium leprae: Strategies, successes, and shortcomings

Molecular epidemiology of leprosy: An update

Molecular epidemiology investigations are notoriously challenging in the leprosy field mainly because the inherent characteristics of the disease as well as its yet uncultivated causative agents, Mycobacterium leprae and M. lepromatosis. Despite significant developments in understanding the biology of leprosy bacilli through genomic approaches, the exact mechanisms of transmission is still unclear and the factors underlying pathological variation of the disease in different patients remain as major gaps in our knowledge about leprosy. Despite these difficulties, the last two decades have seen the development of genotyping procedures based on PCR-sequencing of target loci as well as by the genome-wide analysis of an increasing number of geographically diverse isolates of leprosy bacilli. This has provided a foundation for molecular epidemiology studies that are bringing a better understanding of strain evolution associated with ancient human migrations, and phylogeographical insights about the spread of disease globally. This review discusses the advantages and drawbacks of the main tools available for molecular epidemiological investigations of leprosy and summarizes various methods ranging from PCR-based genotyping to genome-typing techniques. We also describe their main applications in analyzing the short-range and long-range transmission of the disease. Finally, we summarise the current gaps and challenges that remain in the field of molecular epidemiology of leprosy.

Leprosy in Denmark 1980-2010: a review of 15 cases

Background

Leprosy, caused by Mycobacterium leprae, is a chronic and progressive granulomatous disease affecting mainly the skin and the peripheral nervous system. If left unrecognized, the infection can lead to permanent nerve damage and disability. The clinical presentation depends on the immune response of the patient and can result in a wide spectrum of symptoms. Leprosy is a rare encounter in Scandinavia but remains endemic in some parts of the world, with some areas reporting an increasing incidence. We performed a retrospective record review of leprosy cases in Denmark from 1980 to 2010 with the purpose of presenting the most common geographical, demographic and clinical findings and to discuss the diagnostic and therapeutic challenges of patients with leprosy.

Case presentation

In total 15 cases were reviewed. The majority (87 %) of leprosy patients in Denmark were born in South- and Southeast Asia, and were presumed to have contracted the infection in their countries of origin. Patients were predominately young males (mean age: 28.6 years). Anaesthetic skin lesion with or without nerve enlargement were the most common clinical presentations (73 %). Immunological leprosy reactions were seen in 40 % of the cases. Diagnoses were based on clinical findings and skin biopsies. Treatment length varied but all patients received multidrug regimens.

Conclusion

Leprosy should be kept in mind when encountering patients with suspicious skin lesions originating from leprosy endemic areas or with history of travel or work in the tropics. Due to the long incubation period with symptoms presenting long after immigration or return, clinicians often do not have the diagnosis in mind. The wide spectrum of symptoms and immunological reactions further complicates the diagnostic process. Treatment of leprosy and the complicated immunological reactions, which frequently accompanies the infection, should be performed in collaboration with a specialist.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-015-1768-6) contains supplementary material, which is available to authorized users.

New Insights into the Geographic Distribution of Mycobacterium leprae SNP Genotypes Determined for Isolates from Leprosy Cases Diagnosed in Metropolitan France and French Territories

Background

Between 20 and 30 bacteriologically confirmed cases of leprosy are diagnosed each year at the French National Reference Center for mycobacteria. Patients are mainly immigrants from various endemic countries or living in French overseas territories. We aimed at expanding data regarding the geographical distribution of the SNP genotypes of the M. leprae isolates from these patients.

Methodology/Principal findings

Skin biopsies were obtained from 71 leprosy patients diagnosed between January 2009 and December 2013. Data regarding age, sex and place of birth and residence were also collected. Diagnosis of leprosy was confirmed by microscopic detection of acid-fast bacilli and/or amplification by PCR of the M. leprae-specific RLEP region. Single nucleotide polymorphisms (SNP), present in the M. leprae genome at positions 14 676, 1 642 875 and 2 935 685, were determined with an efficiency of 94% (67/71). Almost all patients were from countries other than France where leprosy is still prevalent (n = 31) or from French overseas territories (n = 36) where leprosy is not totally eradicated, while only a minority (n = 4) was born in metropolitan France but have lived in other countries. SNP type 1 was predominant (n = 33), followed by type 3 (n = 17), type 4 (n = 11) and type 2 (n = 6). SNP types were concordant with those previously reported as prevalent in the patients’ countries of birth. SNP types found in patients born in countries other than France (Comoros, Haiti, Benin, Congo, Sri Lanka) and French overseas territories (French Polynesia, Mayotte and La Réunion) not covered by previous work correlated well with geographical location and history of human settlements.

Conclusions/Significance

The phylogenic analysis of M. leprae strains isolated in France strongly suggests that French leprosy cases are caused by SNP types that are (a) concordant with the geographic origin or residence of the patients (non-French countries, French overseas territories, metropolitan France) or (b) more likely random in regions where diverse migration flows occurred.

Leprosy is an old disease that is nearly eradicated from the European continent but not worldwide. The infectious agent, Mycobacterium leprae, has a highly conserved genome, and this property has been used to elucidate the route of its dissemination all over the world. At the French National Reference Center for mycobacteria, 20 to 30 leprosy cases are diagnosed every year, mainly in immigrants from endemic countries or in people living in French overseas territories. A phylogenetic analysis was conducted to investigate the relationship between M. leprae genotypes and the geographical origin of the patients.

The discovery, function and development of the variable number tandem repeats in different Mycobacterium species

The method of genotyping by variable number tandem repeats (VNTRs) facilitates the epidemiological studies of different Mycobacterium species worldwide. Until now, the VNTR method is not fully understood, for example, its discovery, function and classification. The inconsistent nomenclature and terminology of VNTR is especially confusing. In this review, we first describe in detail the VNTRs in Mycobacterium tuberculosis (M. tuberculosis), as this pathogen resulted in more deaths than any other microbial pathogen as well as for which extensive studies of VNTRs were carried out, and then we outline the recent progress of the VNTR-related epidemiological research in several other Mycobacterium species, such as M. abscessus, M. africanum, M. avium, M. bovis, M. canettii, M. caprae, M. intracellulare, M. leprae, M. marinum, M. microti, M. pinnipedii and M. ulcerans from different countries and regions. This article is aimed mainly at the practical notes of VNTR to help the scientists in better understanding and performing this method.

Molecular epidemiology of mycobacteriosis in wildlife and pet animals

The ecology of mycobacteria is shifting in accordance with environmental change and new patterns of interaction between wildlife, humans, and nondomestic animals. Infection of vertebrate hosts throughout the world is greater now than ever and includes a growing prevalence in free ranging and captive wild animals. Molecular epidemiologic studies using standardized methods with high discriminatory power are useful for tracking individual cases and outbreaks, identifying reservoirs, and describing patterns of transmission and are used with increasing frequency to characterize disease wildlife. This review describes current features of mycobacteriosis in wildlife species based on traditional descriptive studies and recent molecular applications.