Dec. 11 (UPI) -- Medical experts have confirmed that 20 people have died from bubonic plague in Madagascar, the worst outbreak of the disease in recent years.
The Pasteur Institute of Madagascar says that tests confirm the villagers, near the north-western town of Mandritsara, died of bubonic plague. This follows a warning issued by the Red Cross in October regarding the island's susceptibility to the disease.
The deaths are worrying because they come outside the island's normal plague season, which runs from July to October, and is also occurring at much lower altitudes than usual.
Some 60 people died from the plague in Madagascar last year out of 200-400 reported cases -- 20 to 33 percent of the world's confirmed plague cases -- and it is largely prevalent in the country's central highlands.
Being off-season and at lower altitudes, health officials are concerned the outbreak could spread more easily to coastal towns and cities.
The bubonic plague, which is transmitted by the Xenopsylla cheeps flea, is predominantly found on black rats. The plague has disappeared from most parts of the world after black rats were replaced by brown rats and health and hygiene conditions improved.
Bubonic plague patients develop swelling in their lymph nodes called buboe, along with flu-like symptoms and gangrene. Even though the disease is treatable with antibiotics, nearly 66 percent of those who do not receive medication die, according to the CDC.