(CNN) The plague -- yes, that plague -- is back in the news. But it never really went away .

But there are almost certainly more than four cases in the world.

Anywhere from 1,000 to 2,000 people get the plague every year, the World Health Organization reported . But that total is likely too modest an estimate, since it doesn't account for unreported cases.

Even by US standards, four cases is unusually low. An average of seven Americans get the plague every year , the Centers for Disease Control and Prevention reported.

Where is the plague most common?

The plague is an endemic disease (meaning it exists permanently) in the Democratic Republic of the Congo, Madagascar and Peru. A 2017 outbreak in Madagascar infected nearly 2,350 people and killed more than 200, WHO reported, though no major outbreaks have been reported since.

In the US, cases are clustered in rural areas in southwest states, like Arizona, New Mexico and Colorado (where plague-carrying prairie dogs canceled camping at a Phish festival outside Denver earlier this year).

How likely am I to become infected?

The plague is still relatively uncommon, though your risk of contracting it might be higher depending on where you live.

There's a risk of human plague wherever humans and animals that contain the plague bacteria co-exist, WHO said.

According to a 2016 map , the possibility of plague exists on almost every continent, especially the western US, parts of Brazil, scattered areas in southeast Africa and large swaths of China, India and the Middle East.

But unless you live among a great deal of wild, disease-carrying rodents, your odds of infection in the US are slim.

How do you get the plague?

That depends on the type. Bubonic plague, the more common form, is caused by bites from infected fleas. It's rarely transmitted between humans.

It's also possible to transmit by handling an infected animal's tissue, as in the case of the Mongolian couple.

Pneumonic plague is the more severe and highly contagious type. Any person infected with pneumonic plague, which originates in the lungs, can infect another person if they inhale droplets from a cough or sneeze.

What are the symptoms?

Every form of the plague starts out similarly -- fever, chills, weakness, headache -- before diverging, according to the CDC.

Bubonic plague manifests as painfully swollen lymph nodes, called "buboes," which can open into pus-filled sores in advanced cases.

Pneumonic plague, since it originates in the lungs, can cause shortness of breath, chest pain and occasionally bloody mucous. It can eventually cause respiratory failure and shock, too.

Another form, septicemic plague, can kill skin and tissue, turning it black, particularly on fingers, toes and the nose.

Can I prevent the plague?

There's no commercial plague vaccine, the CDC said, but it can be treated with antibiotics. Bubonic plague is more easily treated than pneumonic plague, which is almost always fatal unless it's detected and treated early.