Transmission of the mosquito–borne dengue virus appears to be largely driven by infections centered in and around the home, with the majority of cases related to one another occurring in people who live less than 200 meters apart, suggests new research conducted by the Johns Hopkins Bloomberg School of Public Health.

The findings, published in the March 24 issue of the journal Science, offer new insights into the spread of diseases like dengue and how governments and individuals might put in place more targeted and more effective mosquito control programs. The study was also conducted with researchers from the University of Florida, the Walter Reed Army Institute of Research, the Ministry of Public Health of Thailand and the Queen Sirikit National Institute of Child Health.

“What is exciting about this is that we are using new scientific tools to allow us to look inside the black box of disease transmission that we haven’t before been able to penetrate on this scale,” says one of the study’s authors, Justin Lessler, an associate professor of epidemiology at the Bloomberg School. “Understanding the patterns of how infections are spread might help us start to appreciate why certain interventions aren’t working, how some could work better and what we can do to protect more people from what can be a devastating illness.”

Interventions such as mosquito control near the houses of cases and targeted vaccination could potentially be better utilized based on an improved understanding of these patterns.

Forty percent of the world's population live in areas where they are at risk of the virus, which is most common in Southeast Asia and the western Pacific islands and has been rapidly increasing in Latin America and the Caribbean. While most of the 300 million people who get dengue annually survive with few or no symptoms, more than 2 million annually develop what can be a dangerous dengue hemorrhagic fever, which kills more than 25,000 people each year – mostly children.

For their study, the researchers genetically sequenced the viruses of 640 dengue infections that occurred between 1994 and 2010 in both densely populated Bangkok, Thailand, and less densely populated regions outside the capital, then overlaid this information on a map showing where the people infected with the virus lived.

Their results show that in people living fewer than 200 meters apart, 60 percent of dengue cases come from the same transmission chain, meaning they were infected by a virus that was only recently introduced into the area. In people who were separated by 1 to 5 kilometers, just 3 percent of cases came from the same transmission chain.

The researchers also characterized the diversity of dengue viruses across Bangkok. They estimate that 160 separate chains of transmission co–circulate in Bangkok within a season.

Looking across the city, they found that larger populations of humans support a larger diversity of dengue viruses. However, in the areas of Bangkok with the highest population density, they found less diversity than expected.