Tuberculosis in the 21st century: An emerging pandemic?

Abstract

Since the mid-1980ies the world has witnessed a dramatic increase in tuberculosis. Our knowledge of tuberculosis epidemiology was established during the previous epidemic that, at least in Europe, took two hundred years from rise to fall. It is difficult to understand the new epidemic if we assume that the genetics of the host-parasite relationship is unchanged from the previous epidemic. The paper discusses how both host and parasite genetics may have changed. Molecular epidemiology done in Archangel, Russia, where most of the classical reasons for increase in tuberculosis were absent, indicated that strains of Mycobacterium tuberculosis with changed biological properties could be responsible. Strains belonging to the so-called Beijing family were strongly associated with primary drug resistance and caused clusters ten times as big as "traditional" strains. The paper describes how the research consortium takes these observations further to explore the importance of "new" strains of tubercle bacilli in the on-going pandemic. What are the changes in biological properties and what genetic changes do they reflect? The previous epidemic may have changed the genetic susceptibility of the human host by selection, but what has constituted a selective pressure for the bacillary population? The two most dramatic changes in the environment of M. tuberculosis are mass introduction of chemotherapy and BCG vaccination. We explore further the nature of drug resistance in these strains and the possibility that BCG may fail to protect against bacilli of the new pandemic. Lastly the paper points at some action that can be taken instantly and that may have a major impact on transmission, even before the questions mentioned above are answered. The clue here is to shorten the time of transmission by a rapid test to secure early diagnosis and treatment. What is needed, however, is not a diagnostic test for tuberculosis, but a simple screening test with high sensitivity that could tell us whom among the numerous people who have a chronic cough and systemic symptoms who are the true "tuberculosis suspects" eligible for rapid examination of sputum by smear microscopy.