The plague, or the Black Death, is caused by a microbe called Yersinia pestis. In the 14th century, this microscopic enemy killed off a third of Europe's population. While many people consign the plague to centuries past, this attitude is a complacent one. Outbreaks have happened in Asia and Africa over the last decade and the plague is now recognised as a re-emerging disease. In 1996, two drug-resistant strains of plague were isolated from Madagascar. One of these, was completely resistant to all the drugs that are used to control outbreaks.
Anyone interested in bacteria can attest to their ability to evolve resistance to drugs. In the case of drug-resistant plague, the secret to its powers is a plasmid - a small free-floating ring of DNA, that carries drug resistance genes. Bacteria can trade plasmids across individuals, transferring genes between each other in ways that humans can only achieve with ...
