Also known as the Black Death, the bubonic plague seems too terrifying to be true, but the sad fact is that it killed more than 75 million people in 1300s. The horrific spread began in Asia and worked its way into Europe, where about one-third of the continent's population was infected, suffering through myriad symptoms like apple-sized swellings that oozed blood and pus, aches, pains, vomiting, fever and chills, before dying. Although the initial phase wound down around the 1350s, the disease has continued to periodically pop up around the world [source: History].
We now know that bubonic plague is spread by infected fleas and rats, and is best kept under control with public health and improved sanitation efforts [source: History]. That doesn't mean it's history. More than 10,000 people contracted the disease in the Congo between 2000 and 2009. Even in the U.S., 56 people caught the plague during that same period (seven died)[sources: Huffington Post and Bloomberg]. Antibiotic treatment can now quickly cure this once definite death sentence, but it must be done fast. If the bacteria reach the lungs, it becomes pneumonic plague, which can rapidly turn fatal [source: WHO].