At least 20 people in Madagascar are reported to have died from the "Black Plague"; two patients have been diagnosed with the pneumonic plague, an even deadlier strain.

The bubonic plague (Black Plague) is usually spread through flea bites; the pneumonic plague can spread much more easily, and can be transmitted from human to human without the help of parasites, the BBC reported.

The pneumonic plague is almost always fatal if not treated right away, and can kill in a matter of 24 hours. The plague is notorious for having killed a staggering 25 million people in Europe during the middle ages.

The deadly disease first hit Madagascar in 1898, and the region saw five more outbreaks before the 1920s, the Telegraph reported. It then spread inland after that, but Madagascar did not see any additional "serious outbreaks" until 1991 when it hit the coastal town of Mahajanga.

Last year 60 people died from the disease in Madagascar, which was the "highest number reported globally."

The risk of outbreak is believed to be rising due to common unsanitary conditions linked to poverty and overcrowded prisons.

The International Committee of the Red Cross (ICRC) paired up with Madagascar prison authorities to reduce the number of rodents in the local over packed prisons.

"The chronic overcrowding and the unhygienic conditions in prisons can bring on new cases of the disease. That's dangerous not only for the inmates but also for the population in general,"Christoph Vogt, head of the ICRC delegation in Madagascar, told the Telegraph during the time of the campaign.

"Rat control is essential for preventing the plague, because rodents spread the bacillus to fleas that can then infect humans. So the relatives of a detainee can pick up the disease on a visit to the prison, and a released detainee returning to his community without having been treated can also spread the disease," he said.

Bubonic plague sufferers usually experience "fever, headache, chills, and weakness and one or more swollen, tender and painful lymph nodes (called buboes)," the Centers for Disease Control and Prevention (CDC) reported. The illness is often treated with antibiotics.

Victims of the pneumonic plague (which is spread by inhaling microscopic bloody droplets coughed up by other sufferers) tend to experience "fever, headache, weakness, and a rapidly developing pneumonia with shortness of breath, chest pain, cough, and sometimes bloody or watery mucous."