Magazine article Science News

Disease Evolution Plagues Scientists

Magazine article Science News

Disease Evolution Plagues Scientists

Article excerpt

Disease evolution plagues scientists

In the 14th century, the black plague stormed through Europe, killing at least one-quarter of its inhabitants. Then, as mysteriously as it had come, it disappeared. Now molecular biologists have found a clue that may help explain why diseases like the plague rise and fall -- and rise again.

The researchers base their conclusions on studies of two strains of bacteria, Yersinia pestis, which causes plague, and Yersinia pseudotuberculosis, which confers resistance to plague but causes only mild symptoms. Hans Wolf-Watz of the University of Umea, Sweden, with Roland Rosqvist and Mikael Skurnik of the Swedish Defense Research Establishment, first examined two genes believed to help Y. pseudotuberculosis invade cells. The genes code for invasin and Yop1, proteins found at the surface of Y. pseudotuberculosis. Y. pestis contains altered forms of the genes that do not produce proteins. The scientists mutated the Y. pseudotuberculosis genes for invasin, for Yop 1 or for both proteins and administered bacteria containing the altered genes to mice. They then measured the bacteria's virulence by counting the number of mice that died.

The results show that a mutation in one or the other of the two genes barely changes the bacteria's virulence, but mutations in both genes makes the bacteria remarkably more deadly. Apparently, the presence of invasin and Yop1 results in a mild, controlled infection but their absence allows bacteria to ravage cells and cause disease, the researchers say. …

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