Abstract
BackgroundThe reemergence of epidemic diphtheria in Belarus in 1990s has provided us with important information on the biology of the disease and the diversity of the causative agent Corynebacterium diphtheriae. Molecular investigations were conducted with the aim to analyze the genetic variability of C diphtheriae during the post-epidemic period.MethodsThe biotype and toxigenicity status of 3513 C. diphtheriae strains isolated from all areas in Belarus during a declining period of diphtheria morbidity (1996–2005) was undertaken. Of these, 384 strains were isolated from diphtheria cases, 1968 from tonsillitis patients, 426 from contacts and 735 from healthy carriers. Four hundred and thirty two selected strains were ribotyped.ResultsThe C diphtheriae gravis biotype, which was prevalent during 1996–2000, was "replaced" by the mitis biotype during 2001–2005. The distribution of toxigenic C. diphtheriae strains also decreased from 47.1% (1996) to 5.8% (2005). Changes in the distribution of the epidemic ribotypes Sankt-Peterburg and Rossija were also observed. During 2001–2005 the proportion of the Sankt-Peterburg ribotype decreased from 24.3% to 2.3%, in contrast to the Rossija ribotype, that increased from 25.1% to 49.1%. The circulation of other toxigenic ribotypes (Otchakov, Lyon, Bangladesh), which were prevalent during the period of high diphtheria incidence, also decreased. But at the same time, the proportion of non-toxigenic strains with the Cluj and Rossija ribotypes dramatically increased and accounted for 49.3% and 30.1%, respectively.ConclusionThe decrease in morbidity correlated with the dramatic decrease in the isolation of the gravis biotype and Sankt Peterburg ribotype, and the prevalence of the Rossija ribotype along with other rare ribotypes associated with non-toxigenic strains (Cluj and Rossija, in particular).
Highlights
The reemergence of epidemic diphtheria in Belarus in 1990s has provided us with important information on the biology of the disease and the diversity of the causative agentCorynebacterium diphtheriae
The decrease in morbidity correlated with the dramatic decrease in the isolation of the gravis biotype and Sankt Peterburg ribotype, and the prevalence of the Rossija ribotype along with other rare ribotypes associated with non-toxigenic strains (Cluj and Rossija, in particular)
As a result of the implementation of microbiologic screening, a collection of C. diphtheriae strains circulating in Belarus was made at the Institute for Epidemiology and Microbiology in Minsk during 1996–2005
Summary
The reemergence of epidemic diphtheria in Belarus in 1990s has provided us with important information on the biology of the disease and the diversity of the causative agentCorynebacterium diphtheriae. Molecular investigations were conducted with the aim to analyze the genetic variability of C diphtheriae during the post-epidemic period. The diphtheria incidence in Belarus remained higher than in previous decades. Microbiological monitoring currently includes modern molecular biologic and genetic approaches for the investigatation of C. diphtheriae isolates. A variety of molecular methods including multilocus enzyme electrophoresis, ribotyping, pulsed – field gel electrophoresis, and RAPD have been described. All these showed broad circulation of different genotypes and revealed long-term persistence in regions where manifest severe forms of infections have not been registered [1,2]. The genetic population of C. diphtheriae was not constant throughout the epidemic process as confirmed by molecular-epidemiologic methods.
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