An international team has released new estimates of the number of dengue infections around the world, mapping out the places where risk of getting the viral illness is great and those where it's low.
It estimated there are 390 million dengue infections per year, about a quarter of which are "apparent," meaning they are accompanied by symptoms of illness, such as fever or shock. It's a number far larger than the 50 million to 100 million cases a year commonly cited by groups such as the World Health Organization.
A paper describing the researchers' findings was published Sunday in the journal Nature, timed to coincide with the World Health Summit Regional Meeting in Singapore.
There are four different dengue viruses, all passed on to humans in the bites of Aedes mosquitoes. Infection with dengue doesn't always make people sick, but when it does, the symptoms can range from mild fever and muscle aches to a combination of fever, abdominal pain, vomiting and bleeding that can lead to death. There are no effective vaccines or antiviral therapies for the disease. According to the WHO, 22,000 people die from the most severe dengue symptoms, known as dengue hemorrhagic fever, every year. Most are children.
In the past, lead author Simon Hay of the Wellcome Trust and the University of Oxford and his colleagues wrote, global estimates of dengue infections were calculated in a simple manner, and did not break out the differences between regions or over time. But taking more complete data and applying modern mathematical models to estimate infections let the group get a more granular view of the risk on the ground.
The team estimated there were 390 million dengue infections around the world in 2010, the year examined. Of these, 96 million resulted in apparent illness and 294 million did not. Dengue was ubiquitous in the tropics, with high numbers of infections in Asia (which carried 70% of the global burden, with India representing nearly half of those cases) and the Americas (with 14%, more than half of which occurred in Brazil and Mexico). There were more cases than previously thought in Africa, the team wrote -- about 16% of the total. Lots of rain and high temperatures coincided with an area's elevated risk, as did being located near urban centers.
The researchers wrote that using methods like this mapping technique to better understand the variations in dengue risk among regions could help health officials be efficient with surveillance efforts "by indicating where limited resources can be targeted to have their maximum possible impact."
In a statement, Hay said the results suggested that dengue risk would evolve in coming years.
"Climate and population spread were important factors for predicting the current risk of dengue around the world. With globalization and the constant march of urbanization, we anticipate that there could be dramatic shifts in the distribution of the disease in the future," he said. "We hope that the research will initiate a wider discussion about the significant global impact of this disease."
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