February 12, 2008
Return of the Plague
Like no other disease, plague evokes terror. One of the most lethal illnesses in human history, it killed probably a third of Europe’s population in the 14th century. It may also have been one of the first agents of biological warfare: It’s said that in the 1340s, invading Mongols catapulted their plague dead over the city wall into Kaffa in the Crimea.
Yet the plague is not just a disease of the distant past. While cases tapered off in the mid-20th century, the World Health Organization (WHO) now classifies plague as “re-emerging.” No one is predicting another pandemic like the Black Death that devastated Europe. The WHO now records at most only a few thousand cases worldwide per year; and, if detected early, the disease can be treated effectively with antibiotics. But since the early 1990s, plague has returned to places — including India, Zambia, Mozambique, Algeria and parts of China — that had not seen it in many years or even decades. Its global footprint has also shifted, according to a paper published last month in the journal PLoS Medicine. In the 1970s, most plague cases were in Asia; today, more than 90% are in Africa. The conundrum for epidemiologists: Why is human plague reappearing now, even though nearby animal populations have likely harbored the culprit Yersinia pestis bacteria all along?