Stability of DNA Patterns and Evidence ofMycobacterium tuberculosisReactivation Occurring Decades after the Initial Infection

Abstract

Two hundred three freeze-dried strains of Mycobacterium tuberculosis collected during the 1960s were compared with 4102 strains collected during the 1990s, and 14 DNA patterns identified among the "historical strains" were 100% identical to patterns identified among the "recent strains." They were isolated from 41 and 40 patients who had tuberculosis during the 1960s and 1990s, respectively. The patients' mean age differed by >30 years, a finding strongly suggesting that the patients from the 1990s experienced reactivation of M. tuberculosis infection acquired during the 1960s. The half-life of IS6110 DNA patterns during latency was estimated to be 36 years (95% confidence interval, 25-54 years). Thus, this comparison of historical and recent strains yields molecular epidemiologic evidence of M. tuberculosis reactivation spanning decades and suggests that the rate of change of DNA patterns during latency is much longer than that during active disease. This has important implications for the interpretation of clustering, especially for the extent of recent transmission.

Substantial molecular evolution and mutation rates in prolonged latent Mycobacterium tuberculosis infection in humans

“…a few months) to both the one-year-old niece and the latently infected individual. This is also supported by the complete lack of other isolates with the same typing profiles as R94-2977 in isolates collected since nationwide genotyping was introduced (in 1992) (Lillebaek et al, 2003), which is unlikely to have occurred in strains that were actively transmitted between 1961 and 1992. The difference of 5 SNPs and one IS6110-element ( Table 1; Table S5) between Link 1 & 2…”

“…We therefore sequenced a total of 14 Mtb isolates from the two strain collections mentioned above. In total, 6 discrete isolate groups (Links 1-6), inferred from identical RFLP-profiles (Lillebaek et al, 2003), were evaluated. Each link comprised a primary "origin" isolate from the 1960s and a secondary (putatively re-activated) isolate from the 1990s.…”

Stable association between strains of Mycobacterium tuberculosis and their human host populations

“…4. These clades are (16,44), (2,9,10,15,33,43,65,68,72,74), (4,14,23,57,86), (7,56,70), (28,58,84), (47, 55, 67, 69, 95, 97), (46, 79), (76, 83), (18,22,35,40,81), (38,60) where m is the number of terminal clades in the phylogeny, n k is the number of isolates in clade k, d ij is the number of deletions by which isolates i and j differ, and t ij is the number of bands by which the IS6110 fingerprints of isolates i and j differ.…”

“…Calculation of times from phylogenetic branch-lengths measured in numbers of deletions requires an estimate of the number of deletions per year. Direct measurement of mutation events per year has not been attempted for deletions and probably would not be feasible, but it has been performed for IS6110 RFLP band patterns (37)(38)(39)(40)(41). We therefore calibrated the rate of deletions against the rate of change in IS6110 fingerprints.…”

“…First, the rate of change of IS6110 fingerprints is itself uncertain. The instantaneous probability of RFLP band loss or gain is likely to be a nonlinear function of the number of IS6110 in the genome and may depend on the infection's state of activity (37)(38)(39)(40)(41). We therefore considered a fairly wide range of values, assuming that a single band change in IS6110 fingerprint occurs, on average, once every 5-20 years.…”