The plague never went away. Cases are reported in parts of Africa and the US nearly every year

The plague, the rare bacterial infection infamously known for killing tens of millions in 14th-century Europe, never went away . It is now easily treated with antibiotics.

Since the 1990s, most human cases have been reported in Africa, especially Congo and Madagascar, according to the World Health Organization .

There are an average of about seven human cases per year in the U.S., according to the Centers for Disease Control and Prevention , mostly in rural areas of the American West.

A worker at a plague research institute in Siberia recently died of pneumonia. The case has raised alarm in Russia after unconfirmed media reports suggested she might have died of pneumonic plague. Russian authorities say testing showed no evidence of plague, but the research institute has been quarantined.

“People think the plague is gone, it was something that occurred 500 years ago. It’s not. It’s here amongst us,” said Simon Clarke of the University of Reading in the U.K. “Unless you get rid of those wild animals, which of course is not possible, then you’re not going to get rid of the bacteria.”

Surprised to hear the plague is still around? Here’s what to know.

Pneumonic plague and the more well-known bubonic plague – also called the Black Death — are caused by the same bacteria, called Yersinia pestis.

The bacteria spread naturally among rodents like prairie dogs and rats. Fleas that jump from infected animals and bite people can spread the disease.

The bubonic plague is the most common form of the infection. It causes painfully swollen lymph nodes that are most commonly found in the groin, armpit and neck, called buboes. Other symptoms include sudden high fever and chills, headaches, and pain in the abdomen, legs and arms, according to the Cleveland Clinic.

There are two other forms of the plague: pneumonic plague, which can be caused by inhaling the bacteria, infects the lungs. Septicemic plague is an infection in the bloodstream. Both are fatal if not treated early, according to the World Health Organization.

Bubonic plague will often advance and turn into the other two forms of plague if untreated.

Other than bites from infected fleas, people can also get plague by touching infected bodily fluids, so health experts recommend taking extra care when handling dead or sick animals.

The plague can also spread through the respiratory droplets of someone who has pneumonic plague.

“If you cough, you can spread it to another person, but that doesn’t travel very far,” said Dr. Glenn Wortmann, MedStar Washington Hospital Center. “So you really need to be in face-to-face contact with that person to get pneumonic plague.”

That's why “the chance of this spreading widely in Russia and then extending here to the U.S. will not happen,” he said.

The plague was never eradicated, but we’ve gotten better at preventing its spread and treating it in humans.

When treated early with antibiotics, the plague can be cured. The key is to get to a doctor fast — otherwise the plague can be deadly.

There is a vaccine, but the WHO only recommends it for people who are at high risk of infection, like laboratory and healthcare workers. But there isn't strong evidence that vaccines can work against the pneumonic form.

There’s no plague vaccine available in the U.S.

AP video journalist Javier Arciga contributed to this story from San Diego.

The Associated Press’ health and science coverage receives financial support from the AP Fund for Journalism and private foundations. AP is solely responsible for all content. Find AP’s standards for working with philanthropies, a list of supporters and funded coverage areas at AP.org .