What’s up with the bubonic plague?

It sounds like something old. "Bubonic plague."

You hear those two words and you think: "Half of Europe died in the Middle Ages. It was called the Black Death."

You aren't wrong. But it didn't stop there, as many mistakenly believe and as news reports out of Madagascar remind us this week.

The bubonic plague, a deadly infectious disease caused by bacteria, is still very much alive and well, with experts warning of a possible epidemic in Madagascar. 

The concern in Madagascar is in the prisons, since the disease is primarly carried by rats and passed to humans through fleas. Prisons in Madagascar are overrun with rats, and October brings the humid weather associated with a rise in flea activity. 

"If the plague gets into prisons there could be a sort of atomic explosion of plague within the town," Christophe Rogier from the Pasteur Institute told the BBC.

The World Health Organization reports around 2,000 cases of the plague each year, more than 90 percent of which are in Africa, especially Madagascar and the Democratic Republic of Congo. 

Here is a map from the Centers of Disease Control that looks at the global picture of reported plague cases: 

(Centers for Disease Control)

Recent cases of the plague have occurred in Africa, Asia, South America and North America.

Peru saw a significant outbreak in 2010, with 12 people infected. In 2012, there were 256 plague cases in Madagascar, which resulted in 60 deaths — the highest number in the world, according to the International Committee of the Red Cross.

In August of this year, Kyrgyzstan saw its first case in 30 years when a 15-year-old boy died of the plague. 

And the United States is not immune. Cases of the plague were reported in humans in Oregon in 2010 and 2012, as well as in Colorado in 2012. A plague-infested squirrel closed down a park in Los Angeles this July. 

Here's a look at cases of the plague in humans countrywide over the last 40 years, again courtesy of the Centers for Disease Control:

(Centers for Disease Control)

Bubonic plague, as opposed to other forms of the plague, infects the lymph nodes. It has flu-like symptoms and is treatable with antibiotics if identified early. If left untreated the mortality rate can be as high as 60 percent.