For a microscopic organism, Yersinia pestis has made an outsize mark on human history. It has felled some 200 million human beings since it first evolved, in addition to provoking political, economic, social, and cultural upheavals. This toll of death and devastation has earned the disease resulting from this bacterium the right to be called, simply, "The Plague." And though it certainly has a long history, this tiny killer also has a bright future.
Plague has never really disappeared, but it suddenly seems poised for a comeback. Indeed, world health officials have quietly recategorized plague as a "re-emerging" disease in recent years, and it now infects 2,000 people annually, killing 200. The Chinese government even quarantined an entire town this summer after an outbreak of pneumonic plague, which eventually killed three and infected nine more. And experts fear the next stage of the disease will be especially dangerous, fueled by age-old phenomena, such as humans trying to use plague to wage war on their enemies, as well as new ones, such as climate change.
Welcome to the plague years, the next generation. For most people, plague automatically means the Black Death, which began in the 14th century and killed a quarter to a third of Europe's population, roughly 15 million to 25 million people. This is the best-known plague pandemic, but it wasn't the first. That honor goes to a sixth-century outbreak that originated in northern Africa and took out as many as 100 million people. Nor was the Black Death the last major pandemic. Plague spread through China and India during the 19th century, killing some 12 million people, and then spread to the United States in 1900, causing an epidemic in San Francisco.
Between major pandemics, the plague never completely disappeared. It never does: It merely retreats until conditions favor another outbreak. Plague "would be virtually impossible to eradicate," says Ken Gage, chief of the flea-borne diseases branch of the U.S. Centers for Disease Control and Prevention. "The reservoir is rodents, and it's very widespread." Indeed, Y. pestis is endemic in many populations of rats, mice, squirrels, marmots, gerbils, and other rodents. Fleas that feed on these infected animals can pass the disease along to humans. The unlucky recipients usually come down with flu-like symptoms, and death is often a torturous ordeal. All three forms of the disease--bubonic plague, pneumonic plague, and septicemic plague--can be easily cured with antibiotics, assuming it's caught early. When it isn't, the prognosis is poor, with a mortality rate of 50 to 100 percent.
Today, plague is endemic among the rodents of the American Southwest. Isolated outbreaks also occur regularly in East and Southern Africa, Vietnam, Burma, China, Mongolia, Russia, and Central Asia. What's more, there are already troubling signs that the disease is evolving into even more dangerous forms: Scientists recently discovered a drug-resistant strain of the plague in Madagascar.
A perfect storm of factors--including population increases, urbanization, deforestation, changing land use, migration, and the growing ease of travel and trade--are all playing a role in plague's re-emergence. So too, scientists think, is climate change. During the Black Death, the climate was warmer and wetter than usual, which "was very favorable for the plague system," says Nils Stenseth, a biologist and plague expert at the University of Oslo. …