Researchers solve syphilis genome.

Syphilis, a debilitating sexually transmitted disease, has long frustrated researchers. Because it needs a living host to survive, the bacterium that causes the disease cannot be grown in laboratory cultures. To study the disease, scientists have had to use rabbits--an expensive requirement.

"Without being able to use readily available [test-tube] systems, it's been almost impossible to [examine] the biology or virulence of syphilis," says Claire M. Fraser of the Institute for Genomic Research in Rockville, Md.

So, Fraser and her colleagues took another approach to unraveling the secrets of syphilis. They decoded the entire genome of spiral-shaped Treponema pallidum, the bacterium that causes it. Their findings appear in the July 17 Science.

Although syphilis is curable with antibiotics and hasn't become resistant to drugs, understanding its genetic structure remains valuable. For example, the findings may help researchers devise new means of detecting syphilis, which can be asymptomatic.

Also, if the disease mutates into new forms by swapping genes with other bacteria--as some other microbes have done--a genetic blueprint will enable scientists to track those changes, she says. "It's naive to assume that antibiotic resistance won't ever develop," Fraser says.

The genome reveals that T. pallidum has few surface proteins, complicating the search for a vaccine against syphilis. "While it won't be impossible to come up with a vaccine, it will certainly be more difficult than with other bacteria," Fraser says.

Furthermore, the researchers speculate that the dearth of surface proteins on T. pallidum may explain why the body doesn't readily recognize and eliminate the microbe, allowing it to ravage vital organs and tissues, including those in the cardiovascular and nervous systems.