Dengue is classified as an urban disease. Mosquitoes don’t care

The town of Borbón in northern Ecuador is home to several government and religious offices and a regional hospital. Nonetheless, Ecuador classifies Borbón as rural. That designation implies that Borbón’s residents should be relatively safe from dengue, a disease carried by a species of mosquito that, according to the World Health Organization, “lives in urban habitats and breeds mostly in man-made containers.”

But dengue is spreading across Borbón, where the density of these Aedes aegypti mosquitos can mirror that of urban areas, researchers report in the October Social Science and Medicine. Terms like urban and rural have more to do with politics than public health, says epidemiologist Joseph Eisenberg of the University of Michigan in Ann Arbor. “Viruses don’t follow these politically defined entities.”

Misunderstandings over what constitutes an urban or rural area have broad public health implications. Classifying dengue as urban or malaria as rural influences where governments search, track and work to prevent these diseases, leaving less definable regions behind. Those misunderstandings also shape how people respond to such efforts.

In Ecuador, government officials tend to use population density as shorthand for applying the label “urban” or “rural” to a parish, similar to a town or city in the United States. But the almost 100 people Eisenberg’s team interviewed across Esmeraldas province, which includes Borbón, often used a different shorthand — access to government services and amenities, such as trash pickup, a clean water supply and paved roads. Urban areas had such amenities, people said, while rural areas did not. 

Those diverging definitions mean official guidance often doesn’t match local realities. Public health officials in Ecuador request that people living in designated urban areas empty or cover any sources of open water — primary sites for A. agypti mosquitos to lay eggs. Such open sources can include water stored in pots outside or items like trash can lids and flowerpots that collect rainwater. But many people live in neighborhoods classified as rural that have the infrastructure and population density reflective of a city — think Borbón.

Others, meanwhile, live in neighborhoods classified as urban but lack adequate municipal services and amenities. Residents in such areas say that the onus lies on the government to build the infrastructure needed to block spread.

The country’s health officials occasionally distribute bed nets to residents (itself a questionable approach, as dengue-carrying mosquitos are daytime biters). But residents in Esmeraldas say that the purported goals of bed nets still miss the point. Mosquitos swarm puddles in areas without paved roads and storm drains, one resident said. Unless the government fixes those roads, people will continue getting sick from dengue.

Access to more structural services and other amenities do, in fact, appear to be larger drivers of dengue infections than even mosquito abundance, says Sadie Jane Ryan, a medical geographer with the University of Florida in Gainesville. Her work in southern Ecuador has shown, for instance, that widespread availability of air conditioning can reduce dengue, even in areas with many disease-carrying mosquitos. Meanwhile, inadequate plumbing and trash collection increase the risk of dengue.

Ryan’s research, reported in 2021, also showed the unique dangers associated with oft-neglected areas that fall somewhere between the urban–rural dichotomy. People in households with reliable water rarely store water outside, while people in households without plumbing do store water outside but cycle through it quickly, Ryan says. “In that really interesting middle zone where … [people] don’t reliably have access to water, [they] tend to store water long enough for mosquitoes to breed.”

Eisenberg and colleagues argue that curbing mosquito-borne disease transmission worldwide requires overlaying urban-rural maps with other measures of disease risk that decenter the perspectives of distant bureaucrats and center mosquitoes and the people exposed to them. Assemblage theory, for instance, would identify ecological pockets friendly to A. aegypti. Political ecology theories, meanwhile, would factor in the structural forces that facilitate disease transmission, such as unreliable municipal services.

Understanding how mosquito-borne diseases spread is a pressing public health concern as the climate warms and mosquitos find more hospitable climates in which to thrive (SN: 8/26/24). So getting this right matters, say Eisenberg and others.

“Where do epidemiologists … get the notion that ‘urban’ and ‘rural’ make sense as disease descriptors?” asks James Trostle, a medical anthropologist at Trinity College in Hartford, Conn., and a coauthor of the new study. “The mosquito cares about where it can live.”