(CNN) A local folk remedy thought to provide good health had the opposite effect for one Mongolian couple: After eating the raw kidney of a marmot, the pair died of bubonic plague, AFP news agency reported on Monday. Health authorities responded by declaring a quarantine that included locals and foreign tourists who had come into contact with the couple.
Plague, one of the deadliest bacterial infections in human history, caused an estimated 50 million deaths in Europe during the Middle Ages. Symptoms, which usually appear within one to seven days after infection, include painful, swollen lymph nodes, called bubos, as well as fever, chills and coughing.
"After the quarantine [was announced] not many people, even locals, were in the streets for fear of catching the disease," Sebastian Pique, a US Peace Corps volunteer living in the region, told AFP.
Plague has made a recent comeback. Having caused close to 50,000 human cases during the last two decades, it is now categorized by World Health Organization as a re-emerging disease. Worse, the bacterium causing plague, if converted into an aerosolized form, is considered one of the most likely biothreats and is classified as such by the US Centers for Disease Control and Prevention.
Plague affects humans and other mammals, the CDC reports. Usually, people get plague after being bitten by a rodent flea carrying Yersinia pestis, the bacterium that causes the disease, or by handling an infected animal. Cats, which become sick themselves, can directly infect humans, while hardier dogs may simply carry the fleas back to their owners. People also can become sick by inhaling droplets from the cough of an infected person or animal.
The bacteria persists because low levels circulate among populations of certain rodents, the CDC says. These infected animals and their fleas serve as long-term reservoirs for the bacteria.
Plague occurs naturally in the western United States, particularly Arizona, California, Colorado, and New Mexico, where an average of seven human plague cases are reported each year to the CDC.
Plague is found on all continents, except Oceania, according to World Health Organization. Though epidemics have occurred in Africa, Asia, and South America, most human cases since the 1990s have occurred in Africa. Today, the three most endemic countries are the Democratic Republic of Congo, Madagascar and Peru.
In Madagascar, bubonic plague cases are reported nearly every year during the epidemic season, between September and April.
Modern antibiotics -- streptomycin is the usual first-line treatment -- can prevent complications and death if given promptly after symptoms appear. However, a strain of bubonic plague with high-level resistance to streptomycin was seen recently in Madagascar.
The same treatment is used for the two most common types of plague. Bubonic plague has a case-fatality ratio of 30% to 60%, while pneumonic plague, when left untreated, is always fatal, according to WHO.
Over 80% of US cases have been the bubonic form, which is the most common form of infection. Untreated bubonic plague can turn into the more serious pneumonic plague, which causes rapidly developing pneumonia, after bacteria spread to the lungs.
Currently, there is no effective vaccine against plague. While a live attenuated oral vaccine has shown some promise against pneumonic plague, it does not offer protection against bubonic plague, according to one 2015 study.
A recent review of experimental plague vaccines suggests that researchers are exploring a variety of approaches to develop an effective plague inoculation. Since different vaccine designs lead to different mechanisms of immunity, the authors conclude that combinations of different types might overcome the limitations of individual vaccines and effectively prevent the potential plague outbreak.
Key steps for prevention of plague include eliminating nesting places for rodents around your home, sheds, garages and recreation areas by removing brush, rock piles, trash and excess firewood. Report sick or dead animals to law enforcement or your local health officials, do not pick up or touch them yourself. If you absolutely must handle a sick or dead animal, wear gloves.
Use insect repellent that contains DEET to prevent flea bites and treat dogs and cats for fleas regularly. Do not sleep with your pets as this increases your risk of getting plague. Finally, your pets should not hunt or roam rodent habitats, such as prairie dog colonies.