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 when it was known as the Black Death.

“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.

How do you get the plague?

Plague affects humans and other mammals.

The bacteria persists because low levels circulate among populations of certain rodents, according to the CDC. These infected animals and their fleas serve as long-term reservoirs for the bacteria.

Where can you get the plague?

Plague occurs naturally in rural areas in the western United States, particularly Arizona, California, Colorado and New Mexico. That’s where an average of seven human plague cases are reported each year to the CDC. But significantly more cases occur in parts of Africa and Asia.

There are three types of plague – bubonic, septicemic and pneumonic plague. With the pneumonic form of plague – which means it affects the lungs – there is a risk of direct transmission from human to human. That was the case in the large outbreak in Madagascar in 2017, where there were 2,348 confirmed, probable and suspected cases and 202 deaths.

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.

How worried should I be?

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% when left untreated, while pneumonic plague, when left untreated, is always fatal, according to WHO.

More than 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.

Is there a vaccine for the plague?

Currently, there is no effective vaccine against the 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.

How do you protect yourself and your family?

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.

If you live in an endemic area, take added precautions. 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.