Following a study last October that put the dengue burden in India to be about 6 million cases annually, researchers at the Johns Hopkins Bloomberg School of Public Health reveals that the people in southern India have a much higher exposure to the mosquito borne viruses, dengue and chikungunya, than previously suspected.


The researchers, reporting July 16 in PLOS Neglected Tropical Diseases, tested blood samples from 1,010 people across 50 locations in Chennai, a city with over 6 million people in South India, and found that nearly all of them had been exposed to dengue and 44 percent had been exposed to chikungunya. Surprisingly, almost none of the people who had been exposed to dengue reported having been infected by it, either because they weren’t properly diagnosed with the disease or because they didn’t show symptoms.

“Our results show that the extent of the problem has been vastly underestimated,” says the study’s leader Isabel Rodriguez-Barraquer, MD, PhD, a research associate in the Department of Epidemiology at the Bloomberg School.
“People are just not aware of the disease. We asked participants if they had ever been ill with dengue and only one percent of them said yes, when in fact 93 percent had been infected by it.”

Researchers estimated that on average, 23 percent of those who have not yet been infected become infected by dengue every year, corresponding to roughly 228,000 infections per year in Chennai alone. “This rate of infection is extremely high, almost three times higher than in areas of Brazil and Thailand where transmission was thought to be high,” says Rodríguez-Barraquer. They also found that the rate of infection in Chennai was similar in poor communities as in more affluent neighborhoods.

The research is believed to be the first to systematically measure dengue and chikungunya infection rates in India. “If you don’t understand the extent of the problem, you can’t address it,” she says.

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