In locksteppe. A surfeit of gerbils portends plague.

The Lab That Came in From the Cold

A new study linking bubonic plague and gerbil abundance in Kazakhstan could be a boon for public health. Ironically, the research is based on a unique archive that was once part of the Soviet Union's biowarfare program.

The source of the data, the Kazakh Scientific Center for Quarantine and Zoonotic Diseases in Almaty, Kazakhstan, was the linchpin in a network of Soviet antiplague institutes established after World War II to track bacterial diseases. Beginning in the 1960s, the center became a peripheral player in the sprawling Soviet bioweapons program, preparing vaccines against potential battlefield pathogens. Some analysts claim that it also provided pathogens to labs engaged in bioweapons R&D--a charge the current director has denied.

A few years ago, the U.S. Defense Department realized that the center, which had fallen on hard times after the Soviet breakup, posed a potential proliferation threat. After securing the center's collection of nasty bacteria, attention turned to reducing any temptation for center staff to drift off to rogue nations. The European Union and the International Science and Technology Center, a Moscow-based nonproliferation agency, sponsored a group to work with the Almaty center on the ecology of plague outbreaks in Central Asia.The first job was getting the handwritten data--40 years of field observations gathered by hundreds of Kazakh zoologists--transferred onto computer. Then, a team led by Herwig Leirs of the University of Antwerp in Belgium modeled the ebb and flow of plague in populations of the great gerbil, the main host for plague and plague-infected fleas. This analysis showed that the prevalence of plague-infected fleas rises and falls largely in step with the numbers of great gerbils, the team reports in the 30 April issue of Science. "The data set serves as a great backdrop in looking at the evolution and transmission of plague," says May Chu, a microbiologist at the National Center for Infectious Diseases' laboratory in Fort Collins, Colorado.Leirs and colleagues are launching a follow-up study to tackle an outstanding puzzle: where the plague bacterium retreats when gerbils are scarce. Some researchers have argued that plague might, like anthrax, form spores that enter a quiescent stage until gerbil (or other host) populations rebound, while others have suggested that it may simply hang around in the host at low levels. The current study, however, lends support to a third hypothesis: that birds and other migrating animals reintroduce plague to the gerbils via infected fleas.The findings could help cut the risk of people contracting plague. The findings suggest that health authorities should focus scarce funds on tracking gerbil populations and resort to countermeasures when plague is likely to emerge: roughly 2 years after gerbil numbers surpass a threshold.

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The Science paper