[New era in molecular epidemiology of tuberculosis in Japan].

Molecular epidemiology of tuberculosis (TB) is a science to study TB transmission dynamics and to enhance our understanding of the epidemiology of TB by utilizing molecular typing methods as an adjunct to classical epidemiological approach. Before the era of molecular epidemiology, it was quite difficult to ascertain the source of the infections since M. tuberculosis is spread by air-borne droplets of respiratory secretions expelled by an infectious person to a susceptible host and it can remain latent as an asymptomatic infection for years. Now a day, our understanding of TB transmission dynamics has been refined by genotyping of M. tuberculosis strains. The methods of molecular epidemiology, especially IS6110 RFLP of M. tuberculosis, were first introduced to outbreak investigations and then gradually been expanded its application to population-based study in Japan. IS6110 RFLP is obviously a powerful tool for strain differentiation of M. tuberculosis but its labor-intensiveness limits the achievable throughput and makes it less useful for long-term prospective studies. Recently, apart from IS6110 RFLP, DNA amplification-based method, i.e., variable number of tandem repeats (VNTR) has appeared as a substitute for or adjunct to the IS6110 RFLP. In this symposium, we have invited four opinion leaders in molecular epidemiology of TB from different fields: Mycobacterium reference center, basic science, clinical practice, and public health practice. We, as the chairpersons of this symposium, hope that this symposium would trigger the development of molecular epidemiological network of TB in Japan. 1. Achievement and problem of molecular epidemiologic study with IS6110-RFLP analyses of tuberculosis in Okinawa: Shinji MAEDA (Mycobacterium Reference Center, The Research Institute of Tuberculosis, Japan Anti-Tuberculosis Association) The long-term RFLP analyses of tuberculosis in Okinawa showed that endemic M. tuberculosis might be present. This is one of the achievements of our project study. On the other hand, for more effective examination of contact persons, information of molecular epidemiology should be used actively. Therefore because the analysis report needs to be sent back quickly, the PCR-based VNTR method should substitute for the RFLP analysis. 2. Basic knowledge and application of Variable Numbers of Tandem Repeats: Kei NISHIMORI (Department of epidemiology, National Institute of Animal Health) Genomic loci of Variable Numbers of Tandem Repeats (VNTR loci) in Mycobacterium tuberculosis complex and Mycobacterium avium, the history of analysis of VNTR loci, the hypothetical mechanisms of increase or decrease of number of repeats, the structures of the loci, and the necessity of standardizing the VNTR typing were introduced. 3. Clinical application of VNTR: Tomoshige MATSUMOTO, and Hiromi ANO (Department of Clinical Research and Development, Osaka Prefectural Hospital Organization Osaka Prefectural Medical Center for Respiratory and Allergic Diseases) Tuberculosis genotyping was first introduced to outbreak investigations and population-based studies. The advent of Variable Numbers of Tandem Repeats (VNTR) can be applied to clinical fields of not only Mycobacterium tuberculosis but also of Mycobacterium avium. In Osaka Prefectural Medical Center for Respiratory and Allergic Diseases, clinical application of VNTR was first introduced in Japan to determine whether Mycobacterium tuberculosis or avium disease was caused by reactivation or reinfection when relapsed. We showed some examples about usefulness of the clinical application of VNTR. 4. Molecular epidemiology of tuberculosis to improve TB prevention and control activities: Tomotada IWAMOTO (Department of microbiology, Kobe Institute of Health), Riyo FUJIYAMA, Noriko TANAKA, Yasuto KAWAKAMI (Kobe City Public Health Center), Chika SHIRAI (Hyogo-ku Health and Welfare Department, Kobe) M. tuberculosis isolates in Kobe have been characterized as: a) Beijing family strains are highly prevalent (77%), b) two major MIRU profiles in Beijing family were found, one is globally pandemic genotype and the other is locally prevalent strains, c) six strains belonged to T3-Osaka family, and d) Manila family strains made cluster consisting of 3 strains. Kobe VNTR Database which consists of 12-loci MIRU and 9 additional VNTR loci has been developed. The basis for the selection of these supplemental 9 VNTR loci and the application of VNTR database in TB control program were introduced.