Densely populated communities may experience higher likelihoods of dengue transmission when people are closer than 200 meters apart, with infections from the same strain occurring in and around the home, according to research published in Science.
“What is exciting about this is that we are using new scientific tools that allow us to look inside the black box of disease transmission that we haven’t before been able to penetrate on this scale,” Justin Lessler, PhD, associate professor of epidemiology at the Bloomberg School of Public Health at John Hopkins University and an author in the study, said in a press release. “Understanding the patterns of how infections are spread might help up 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.”
As dengue is most prelevant in tropical urban areas, researchers observed the patterns of dengue cases in both Bangkok, Thailand, and surrounding areas, and then assessed the relations of chains of singular transmissions. Data concerning 800 geolocated genotype cases and 17,291 serotype cases of dengue that occurred between 1994 and 2010 were analyzed.
For individuals living in Bangkok, one transmission chain of dengue caused 60% of transmissions (average = 1,300 cases) in individuals located closer than 200 meters from each other. When more isolated areas were analyzed, only 3% of dengue cases between 1 and 5 kilometers from each other shared the same transmission chain.
Cases of dengue that were geographically condensed demonstrated a total of 1.7 chains, and this number increased by a factor of 7 for every 10-fold population increase in condensed areas whether the density or area of the location increases or not. However, no additional chains were found once the density of an area reached 7,000 people per square kilometer or higher.
Although the chance of transmission of the disease within a single area is high, researchers noted that the virus’ flow to surrounding countries was minimal.
“Our findings suggest that large urban centers provide a source of dengue diversity that could possibly be dispersed to other areas of the country and the world,” researcher Derek A.T. Cummings, PhD, professor of biology at University of Florida’s Emerging Pathogens Institute, said in a press release. “But the fact that diversity saturates at the large population densities also suggests that these areas might be areas where intense competition is occurring between dengue viruses.” — by Katherine Bortz
Disclosure: The researchers report no relevant financial disclosures or conflicts of interest.