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[HANOI] In a challenge to conventional scientific wisdom, a study in Vietnam has claimed that people in rural areas — not cities, as widely believed — face the highest risk of contracting dengue fever.

Tests on about 3,000 hospital patients conducted in south-central Vietnam between 2005 and 2008 found that rural areas "may contribute at least as much" to dengue epidemics as cities do.

This is despite the fact that cities "contribute substantially" because they are more populated, according to a team of researchers led by Wolf-Peter Schmidt of Nagasaki University's Institute of Tropical Medicine.

The study, whose results are published in the August issue of PLoS Medicine, draws attention to the link between high dengue infection rates and a lack of tap water in rural areas.

In villages with minimal tap water supplies, water storage vessels are breeding sites for dengue-infected mosquitoes, says the study.

"There is probably a location-specific element to their findings, so if you replicated [the study] in northern Vietnam, you might have a different set of findings," said Cameron Simmons, an immunologist at the Oxford University Clinical Research Unit in Vietnam's southern hub, Ho Chi Minh City.

"Nonetheless, it's important for people to understand that dengue transmission is not just restricted to big, crowded areas," Cameron told SciDev.Net.

Dengue fever infects 50 million people living in tropical and subtropical regions each year. There is no vaccine available, but the French company Sanofi plans to release one in 2014.

The disease occurs throughout Vietnam, particularly in the southern provinces in summer, and is typically accompanied by headaches and other symptoms.

Vietnam should provide steady supplies of tap water to rural villages, said Vu Dinh Thiem, an epidemiologist at the National Institute of Hygiene and Epidemiology in Hanoi and co-author of the study.

In a typical case, Thiem told SciDev.Net, "a village will have water for two days, but the next day they won't. The people have to use a container to store the water, which increases the risk of dengue."

The study is being submitted to Vietnam's Ministry of Health.

Link to full paper in PLOS Medicine


PLoS Medicine doi: 10.1371/journal.pmed.1001082 (2011)