Aedes aegypti mosquitos have a vast range around much of the planet where they spread dengue fever, yellow fever, Zika, chikungunya and other debilitating and often deadly diseases. The insects are typically active during the day so we are safe from them after dark.

Or are we?

Artificial light in populated areas increases the biting behavior of the pesky mosquitoes, say researchers from the University of Notre Dame. The females of the species (the only ones that bite) normally feed early in the morning and later in the afternoon, but light pollution causes them to stay active even after sunset, according to the scientists.

A researcher, who is the lead author of a newly published paper, found that out by letting female mosquitoes kept in a lab bite his arms under controlled conditions: during the day, at night or at night illuminated by artificial light. “As predicted from the Ae. aegypti biting cycle, maximal biting occurred during daytime and lowest level occurred at night,” the scientists explain in their study.

Yet, they add, mosquitoes that were exposed to artificial light at night (ALAN) were fond to be more active after dark than those that were not. In fact, the mosquitoes were twice as likely to bite at night when they were exposed to artificial light.

“These data reveal that exposure to ALAN increases nocturnal blood-feeding behavior,” the experts note. “This finding highlights the concern that globally increasing levels of light pollution could be impacting arboviral disease transmission, such as dengue fever and Zika, and has implications for application of countermeasures for mosquito vector control.”

Needless to say, this finding has grave implications for our efforts to combat mosquito-borne diseases in tropical and subtropical areas where Aedes aegypti mosquitos thrive.

“This is potentially a very valid problem that shouldn’t be overlooked,” says Giles Duffield, at associate professor at the university’s Department of Biological Sciences. “[These mosquitoes] live and breed in the vicinity of houses, so the chances of Aedes aegypti being exposed to light pollution are very likely.”

Of dengue fever alone, as many as 390 million infections occur worldwide each year with around half a million people developing severe symptoms of dengue hemorrhagic fever, of which some 25,000 people die annually.

That mosquitoes spread diseases like dengue fever even when we think we are safe from them should be a wake-up call to epidemiologists, Duffield notes. “The impact of this research could be huge, and it probably has been overlooked,” he says. “Epidemiologists may want to take light pollution into account when predicting infection rates.”

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