Scientists have warned that plague, scourge of the medieval world, poses a "a growing but overlooked threat" as it spreads slowly into hitherto unaffected territories.
According to a team including Michael Begon, an ecologist at the University of Liverpool, while plague has "only killed some 100 to 200 people annually over the past 20 years", it has popped up in new countries in the last few decades, notably in Africa.
Reuters notes that the World Health Organisation reports about 1,000 to 3,000 plague cases annually, with most in the last five years occurring in Democratic Republic of Congo (which saw hundreds of suspected cases in an outbreak of pneumonic plague in 2006), Madagascar, Malawi, Mozambique, Tanzania and Uganda.
The disease - which is caused by the Yersinia pestis bacterium and spread by fleas carried on animal vectors, notably rodents - comes in two equally unpleasant flavours: bubonic, provoked by flea bite and characterised by the black skin bubos which led to it being dubbed the "Black Death"; and pneumonic, which is caused by infection via the lungs.
In the former, Yersinia pestis causes haemorrhagic inflammation of the lymph nodes which swell to form the aforementioned bubos. The nodes subsequently drain into the bloodstream, allowing the bacterium to attack the entire organism. Symptoms include high fever, headache and muscle aches.
In the latter, the infection provokes high fever, signs of pneumonia including chest pain and difficulty breathing, nausea and vomiting, although the victim is spared the bubos.
Either form of infection may develop into septicemic plague* when Yersinia pestis multiplies rapidly in the bloodstream, rather unpleasantly causing fever and chills, diarrhoea and vomiting, bleeding from the mouth, nose or rectum or under your skin, and gangrene in the extremities, most commonly fingers, toes and nose.
While plague is easily treated with antibiotics, this may not be an available option in the developing world. Begon and his colleagues warned: "Although the number of human cases of plague is relatively low, it would be a mistake to overlook its threat to humanity, because of the disease's inherent communicability, rapid spread, rapid clinical course, and high mortality if left untreated."
The team accordingly called for "more research into better ways to prevent plague from striking areas where people lack access to life-saving drugs and to defend against the disease if used as a weapon".
They concluded: "We should not overlook the fact that plague has been weaponised throughout history, from catapulting corpses over city walls, to dropping infected fleas from airplanes, to refined modern aerosol formulation."
The team's research can be found in the Public Library of Science journal PloS Medicine. ®
*Septicemic plague can also be considered a third form of the disease if contracted by the direct entry of Yersinia pestis into the bloodstream, rather than via the lymph nodes.