Diversity of Mycobacterium tuberculosis genotypes circulating in Ndola, Zambia

Abstract

BackgroundTuberculosis (TB) is one of the major public health problems in Zambia. However, information about lineages of M. tuberculosis complex (MTBC) isolates useful for epidemiology investigations is unknown. In this study, we investigated the diversity of MTBC isolates from Ndola, a typical Zambian urbanized city with a documented high HIV prevalence.MethodsThis was part of a prospective cohort study in subjects with sputum smear-positive pulmonary TB. Spoligotyping was used to genotype the MTBC isolates and establish the circulating lineages. The 15-locus Mycobacterial Interspersed Repetitive Units - Variable Number Tandem Repeats (MIRU-VNTR) typing was used to study recent transmission.ResultsA total of 98 different spoligotypes were identified among 273 MTBC isolates. The majority (64.8%) of the isolates belonged to 9 known families, while 96 (35.2%) of the isolates were orphans. While LAM (41.8%) was the largest spoligotype family observed, most of the isolates (87.7%) belonging to the SAF1 family, with a significant portion coming from the T (13.6%), and X (5.9%) families. A few isolates (3.6%) belonged to the CAS, EAI, H, S, X1-LAM9 or U families. MIRU-VNTR typing was highly discriminatory (h = 0.988) among the 156 isolates tested in our sample, and increased the discrimination among 82 SAF1 isolates from 6 to 46 distinct patterns. In addition, 3.2% (5/156) of cases with available MIRU-VNTR results harbored more than one MTBC strain.ConclusionsOur findings show a limited diversity of MTBC in Ndola with a high clustering rate (37.7%), which indicates that recent transmission plays an appreciable role in the dynamics of TB disease in this setting. This conclusion emphasizes the importance of early diagnosis and timely treatment. The results also confirm that MIRU-VNTR typing is suitable for studying the molecular epidemiology of TB in Ndola.

Predominant Mycobacterium tuberculosis Families and High Rates of Recent Transmission among New Cases Are Not Associated with Primary Multidrug Resistance in Lima, Peru

“…Compared with other infectious diseases, however, for which 20% of the population may generate 80% of transmission, TB transmission appears relatively more homogeneous (53,54). Previous studies in areas with high TB incidence rates have shown a wide range of transmission rates (clustering rates), ranging from 37 to 72% in settings with TB incidence rates of over 200 cases per 100,000 inhabitants (55)(56)(57).…”

Mycobacterium tuberculosis polyclonal infections and microevolution identified by MIRU-VNTRs in an epidemiological study

“…Since the present report presents essentially MIRU-VNTR data, hereafter the focus will be on microevolution concerning this particular marker. Most often, studies on polyclonal and multiple strain infections were conducted in settings with high TB burden [2][3][4][5]. Nevertheless, they have also been observed in areas with moderate TB incidence [6].…”

“…MIRU-VNTR typing [8,9], widely applied in molecular epidemiologic studies, facilitates the detection of polyclonal infections as the presence of more than one strain in a sample is likely to lead to the detection of multiple alleles in a number of loci. Depending on the number of implicated loci, two distinct mechanisms are considered responsible for the presence of such multiple alleles; ''inpatient'' microevolution of the infecting clone in case of the detection of double alleles in a single locus as opposed to simultaneous infection with two distinct MTB strains when two or more loci are concerned [2][3][4]10]. Microevolution can of course affect any genotypic marker, for example, a strain may evolve by losing a spacer of the initial spoligotype profile.…”

Molecular epidemiologic tools for diagnosis of tuberculosis: A Review of literature and its applicability in Nigeria

“…Such information is valuable for the development of new tools for TB control (Gagneux and Small, 2007). Furthermore, apart from differentiating MTBC strains, MIRU-VNTR typing can easily identify mixed infections in patient isolates (Mulenga et al, 2010).…”

“…Some of the more popular MTBC typing methods being used globally include IS6110-based restriction fragment length polymorphism (RFLP) (Van Embden et al, 1993), PCR based methods such as spoligotyping (Kamerbeek et al, 1997), mycobacterial interspersed repetitive unitsvariable number of tandem repeats (MIRU-VNTR) (Frothingham et al, 1998), single -nucleotide polymorphisms (Gutacker et al, 2006) and largesequence polymorphism analysis (De Jong et al, 2009;Mulenga et al, 2010).…”