Bubonic plague, caused by bacteria called Yersinia pestis, is usually transmitted to humans through bites from infected fleas carried aboard rodents, notably rats. The disease first emerged in China more than 2,600 years ago, and spread to Western Europe and Africa via the Silk Road trade routes of the Middle Ages. In 1347, a fleet of Genoese trading ships arrived in the Sicilian port of Messina, with their sailors either dead or gravely ill from a mysterious disease that covered them with black boils (hence the name “Black Death”). The plague quickly spread, eventually killing upwards of 20 million people–nearly a third of Europe’s population–before it subsided in the early 1350s.
At that time, people had no idea how bubonic plague was spread, or how to treat it; many people even believed the disease was a punishment from God for human sins, including heresy, greed, blasphemy, fornication and worldliness. The Black Death reappeared every few generations over the ensuing centuries, but largely disappeared from Europe thanks to modern medicine and improving sanitary conditions.
Bubonic plague first appeared in Madagascar, an island nation in the Indian Ocean off the southeastern coast of Africa, in 1898. The country saw successive outbreaks until the 1920s, after which the disease disappeared from coastal areas but began appearing in inland areas with higher elevations. The first serious outbreak in years occurred in 1991, around the coastal town of Mahajanga, and by the end of the 1990s health experts warned that the disease seemed to be spreading to lower altitudes again.
After a political coup in 2009, living standards in Madagascar have seriously deteriorated, and continuing political unrest has exacerbated the problems. Madagascar now reports some 200-400 confirmed cases of bubonic plague each year to the World Health Organization (WHO); this makes up one-third to one-fifth of globally reported cases. The country’s prisoners are usually among the most affected on the island, due to the high number of rats in its overcrowded prisons.
This October, the International Committee of the Red Cross warned that Madagascar was at risk for a plague epidemic. Then, after 20 people living in a remote village located near the northwestern town of Mandritsara died last week, tests by the Pasteur Institute of Madagascar confirmed they died of bubonic plague. Health officials, who have gone to the region for further investigation, see the outbreak as particularly worrying as it occurred outside the usual plague season (July-October) and at a far lower elevation than usual, suggesting that the disease may be spreading.
Victims of bubonic plague often develop painful swelling in the lymph nodes (known as buboes); flu-like symptoms such as fever, chills, vomiting and diarrhea; and gangrene. The disease can be treated with antibiotics but has a high mortality rate: Nearly two-thirds of those infected with plague will die, according to the U.S. Center for Disease Control (CDC). Today, bubonic plague can be easily diagnosed with a rapid dipstick test, and a vaccine may be available within a decade.
Scientists believe bubonic plague first came to the United States around 1900, in Asian rats that escaped from ships in the ports of San Francisco and Los Angeles. It was initially confined to cities (the worst outbreak occurred after the 1907 earthquake in San Francisco) but later spread inland. Today, an average of seven U.S. cases of plague are reported every year, mainly in the mountainous Southwest, where pack rats, ground squirrels and prairie dogs may carry infected fleas. The United States ranks 11th in the world in cases of plague, with some 57 cases reported in the last decade, according to a survey published in September by the American Journal of Tropical Medicine and Hygiene. The United States was the only wealthy country on the list. Ninety-seven percent of reported cases in the study were in Africa; Congo ranked first, with 10,581 cases, and Madagascar second, with 7,182.