Cholera, a potentially fatal disease that has come to symbolize the humanitarian crisis of the war in Yemen, has surged again in the country, health workers reported Wednesday, with some areas hit by as many as 2,000 suspected or confirmed cases per week.

Doctors without Borders, the medical charity, said in a statement that its teams had recently seen a “dramatic increase in cholera cases, demonstrating the urgent need for humanitarian assistance to improve water and sanitation in the war-torn country.”

The World Health Organization said that from the beginning of 2019 through March 17, nearly 109,000 cases of severe acute watery diarrhea and suspected cholera had been reported, with nearly 200 deaths. About one-third of the reported cases afflicted children underage 5, the organization said.

Spread by poor hygiene and contaminated drinking water, cholera can cause fatal dehydration without treatment. It has long been considered endemic to Yemen, the Arab world’s poorest country.