In a massive study that examined data from 76 countries collected from 1959 to 2009, analysts from the University of Illinois have found that outbreaks of chikungunya and dengue fever — both linked to mosquitoes — are most affected by population density and proximity to a country already experiencing an outbreak.
Chikungunya and dengue are both potentially deadly viral diseases with overlapping distribution and high prevalence in tropical and subtropical regions.
“As a geographer, I was glad to see that the first law of geography held true, which is that things that are near each other tend to be more alike,” Marilyn O’Hara Ruiz, University of Illinois pathobiology professor and study lead, said. “In general, when we look across time, these things are quite localized in that countries that are near each other are more likely to have the same outbreak.”
Researchers said an unexpected find was that the diseases are largely unaffected by local temperature or precipitation, which tend to dictate where mosquito populations will congregate.
Ruiz worked alongside University of Illinois pathobiology professor Rebecca Lee Smith and former postdoctoral research associate Gianluigi Rossi on the study. Ruiz said the findings should reassure those worried about distant outbreaks that will travel across the world and should alleviate some concerns as the reduction of disease spread can benefit from resources focused on high density and outbreak-adjacent populations.
The study did, however, highlight the need to share health data with neighbors.
“People sometimes don’t want to share that they have an outbreak going on,” Ruiz said. “But mosquitoes don’t recognize borders. So, we need epidemiology without borders.”