Ancestral Mycobacterium tuberculosis genotypes in India: implications for TB control programmes

Abstract

It has been a decade since the genome sequence of Mycobacterium tuberculosis was unraveled. The fruits of genomic technologies are yet to reach high burden countries such as India, where tuberculosis (TB) kills a huge number of patients. Paradoxically, despite increased cases of human immunodeficiency virus (HIV) infection and diabetes mellitus, TB cure rates in India have been consistently improving during the DOTS program. Does this mean that the underlying TB bacilli are somehow 'co-operating' with the TB control program implementers ? Genotypic analyses of the tubercle bacilli have identified a predominance of ancestral strains of M. tuberculosis in major parts of India in addition to various other lineages of modern evolutionary descent. Virulence and dissemination potentials of these ancestral strains are speculated to be 'low' as compared to the other 'aggressive' strains such as Beijing and LAM, which are expected to be more widespread in future, also in synergy with HIV and diabetes epidemics. We discuss the implications of the high prevalence of ancestral strains on TB control in India. It appears that despite a hypothetical 'ancestral advantage', future dynamics of tubercle bacilli in the back drop of surging HIV and diabetes incidences may pose a major healthcare problem in India in the years to come.