Diversity Among TB Strains Might Contribute to Drug-Resistance, Study Says

There is greater diversity among tuberculosis bacteria than previously thought, which could be a contributing factor to the increase in multi-drug resistant TB, according to a study published recently in the journal PLoS Biology, SciDev.Net reports.

For the study, the researchers examined genes in 99 strains of Mycobacterium tuberculosis, including nine animal-specific strains, and found that greater genetic diversity exists between human TB strains than animal strains. This finding contradicts the previous belief that all human TB strains were identical. The study also found that TB bacteria undergo low rates of genetic selection, which prevents drug-resistant mutations from being removed from the gene pool.

In addition, the study found that human TB falls into two geographically distinct groups: "ancient" strains that are found only in West Africa and along the rim of the Indian Ocean, and modern strains predominantly found in Europe, the Americas, East Asia, East Africa and India. The researchers suggested that geographic strain diversity, along with global travel, be considered in designing TB control programs, SciDev.Net reports (Harvey, SciDev.Net, 12/30/08).

The study is available online.