The number of people infected by two mosquito-borne viruses - dengue and chikungunya - is much higher than reported, a study by researchers at a US university has found.
The study, involving 1,000 people across 50 locations in Chennai, found that almost none of those exposed to dengue reported it.
"Our results show that the extent of the problem has been vastly underestimated," said study leader Isabel Rodriguez-Barraquer, research associate in the Department of Epidemiology at the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland.
"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," Rodriguez-Barraquer noted.
Even though dengue is believed to be present in India since the 1940s, it is only in the past few years that there is growing recognition of the magnitude of the problem.
The researchers estimated that on an 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," RodrAguez-Barraquer noted.
Chikungunya is marked by fever and joint pain and other symptoms may include headache, muscle pain, joint swelling or rash.
Dengue virus is the most rapidly spreading virus transmitted by mosquitoes and is a major source of illness in the tropics and subtropics, infecting as many as 400 million people annually.
There are not yet any vaccines to prevent infection with dengue virus.
"Often, it is not the first but the second time someone is infected with dengue virus that can be deadly," Rodriguez-Barraquer pointed out.
These findings, the researchers said, reinforce the need for officials to be on the lookout for these diseases and to find ways to control its spread in India.
