May 5, 2004
Peter Small, M.D., of Stanford University, and colleagues examined the genomes of the TB strains to identify specific, irreversible genetic changes that served as "fingerprints." His team used genetic analysis to discriminate between TB cases contracted from another San Franciscan and cases that arose from much earlier infections.
Using those fingerprints, the researchers could track transmission through a community, said Aaron Hirsh, Ph.D., lead author of the second paper. That information could be graphically represented to illustrate commonalities between strains. Researchers assigned each strain its own color, based on the national origin of the infected person.
"It was amazing how clearly the tree was pink in one branch and blue in another branch and black in another branch," said Hirsh. "It fell out so neatly, based on where a person was born, even though half those people had gotten their tuberculosis after they arrived in the city." "I suspect the most reasonable explanation has to do with sociology," said Hirsh.
"Co-evolution is highly speculative, but it's an intriguing possibility," said Small. "This has profound implications for vaccine development. We may ultimately need to develop different vaccines for different parts of the world. It's a completely open question, but we can start to answer it now."
The papers "Functional and Evolutionary Genomics of Mycobacterium tuberculosis: Insights from Genomic Deletions in 100 Strains," and "Stable Association Between Strains of Mycobacterium tuberculosis and Their Human Host Populations," appeared in the same edition of Proceedings of the National Academy of Sciences (2004;101(14):4865-4870 and 4871-4876, respectively).
TB & Outbreaks Week