Burkina Faso's health ministry has declared a dengue fever epidemic amid the deadliest outbreak in years. More than 200 people have died, and new cases are rising sharply.

There have been 50,478 suspected cases and 214 deaths of the mosquito-borne illness this year, the ministry said in a statement released on Wednesday, mostly in the urban centers of the capital, Ouagadougou, and Bobo Dioulasso. It said about 20% of the cases and deaths were recorded last week alone.

Dengue kills an estimated 20,000 people worldwide each year. Rates of the disease have risen eightfold since 2000, driven largely by climate change, the increased movement of people and urbanization.

The World Health Organization this month warned that the disease would become a major threat in new parts of Africa as warmer temperatures create conditions for the mosquitoes carrying the infection to spread.

Dengue is spread by infected Aedes aegypti mosquitoes. Symptoms include fever, muscle pain, nausea and rashes. Lack of treatment or misdiagnosis, common in poverty-stricken countries such as Burkina Faso where health care is spotty, increase the chance of death.

Burkina Faso's outbreak dwarfs other African outbreaks in recent years. According to figures from the Africa Centers for Disease Control and Prevention, dengue killed 18 people in Burkina Faso in 2017 and 15 in 2016.

The health ministry said that it was providing free rapid diagnostic tests and had organized spraying of insecticide in public places to counter the spread.