Dengue fever has infected almost 20,000 people in Vietnam in the first six months of the year and killed 21, seven more than in the same period last year, the health ministry said Friday.
Higher temperatures and rainfalls have been blamed for the nearly 15 percent rise to 19,144 new infections from the mosquito-borne disease, which have been concentrated in the poverty-stricken southern Mekong delta.
Malaysia and other Southeast Asian countries have also seen surging cases of the virus that causes flu-like symptoms, aching joints and fatigue.
"Vietnam's worst hit provinces were in the Mekong delta," said Tran Thanh Duong, an official with the ministry's preventive health care department.
"The increased infection rate is mainly due to unusually hot weather and too much rain this year, which has provided good breeding grounds for mosquitos."
The virus thrives in urban areas because the carrier, the aedes mosquito, breeds in stagnant water, including in blocked drain-pipes and rubbish heaps.
Experts predict dengue fever will increasingly spread with global warming, growing urbanisation and more international travel.