WHO says 40% of population at risk for dengue fever

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Jan 24, 2012 (CIDRAP News) – The World Health Organization (WHO) sounded a new warning today about the spread of dengue fever, saying cases have increased sharply since 2008 and more than 40% of the world's population is at risk for infection.

Official reports show that cases in the Americas, Southeast Asia, and the western Pacific exceeded 2.2 million in 2010, compared with just 1.2 million in 2008, the agency said. The Americas alone had 1.6 million cases in 2010. That included 49,000 cases of severe dengue, also known as dengue hemorrhagic fever, the WHO said.

The agency estimates the global total of dengue cases at 50 million to 100 million, with most of them going unreported. An estimated 500,000 people worldwide, many of them children, are hospitalized with severe dengue each year.

"Today, severe dengue affects most Asian and Latin American countries and has become a leading cause of hospitalization and death among children in these regions," the statement said. It called dengue "a major international health concern."

The disease, caused by a mosquito-borne virus, is now endemic in more than 100 countries in Africa, the Americas, the eastern Mediterranean, Southeast Asia, and the western Pacific, the WHO said. Before 1970, only nine countries had faced severe epidemics.

"Not only is the number of cases increasing as the disease spreads to new areas, but explosive outbreaks are occurring," the agency said. Outbreaks are now possible in Europe, following the first reports of local transmission in France and Croatia in 2010.

Dengue is spread chiefly by Aedes aegypti mosquitoes, which live in urban areas and breed mostly in man-made containers, the WHO noted. The mosquitoes are daytime feeders, with peak biting periods early in the morning and before dusk.

A secondary vector of the virus is Aedes albopictus, an Asian mosquito that can tolerate lower temperatures than A aegypti and has spread to North America and Europe because of the international trade in used tires.

There are four dengue virus serotypes. Infection with one of these provides lifelong immunity against that strain, but only partial, temporary protection against the other three, and later infections with any of the other three types can increase the risk of severe disease, the WHO noted.

There is no specific treatment for dengue, but the WHO said that in severe cases, "care by physicians and nurses experienced with the effects and progression of the disease can save lives," reducing the mortality rate from more than 20% to less than 1%.

No vaccine for dengue has been approved, but several candidate vaccines are in clinical trials. For now, the only effective prevention and control strategy is to combat carrier mosquitoes, the WHO noted.

See also:

Jan 24 WHO statement

May 16, 2011, CIDRAP News item about Sanofi Pasteur's candidate dengue vaccine

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