Light pollution could make West Nile virus in birds more infectious, study suggests
CHICAGO – Light pollution can extend by 41 percent how long sparrows are infectious with West Nile virus, which could make it more likely that they transmit the lethal disease to mosquitoes and on to people, a new study from researchers in Florida has found.
Meredith Kernbach, a University of South Florida doctoral candidate and lead researcher, recently published her findings in Proceedings of the Royal Society B.
“This is really the first study that’s kind of investigating the effects of light pollution on infectious disease,” Kernbach said in an interview. “We have to admit this is a captive (laboratory) study, but if we see something similar in urban areas near people, it may increase the opportunity for spillover to humans.”
Kernbach chose house sparrows because they often live in urban areas and because they’re a good example of what’s known as a reservoir species, which doesn’t often die from West Nile but can pass it on to mosquitoes. The study exposed some birds to light at night, with the control group in darkness then, she said. The birds exposed to artificial light stayed sick with West Nile an average of two days longer than the control group.
“We also know light pollution has a lot of negative consequences for animals and people. It’s a real threat,” Kernbach said. “So we wanted to examine the direct role of light in fighting infection.”
Birds use light cues as part of daily and seasonal rhythms, informing what time they begin chirping as well as when to migrate or produce young, said Doug Stotz, a bird expert at the Field Museum.
Kernbach’s study, however, may be the first indication that light pollution can affect the spread of zoonotic diseases, ones that can pass from animals to people.
Patrick Irwin, assistant director of the Northwest Mosquito Abatement District, read the study and has had many conversations with other scientists about its implications.
“This is something that has a lot of people in my field excited, and I’ll admit, it’s not something I would’ve thought of,” Irwin said. “But it’s awesome that somebody did and now we have at least some idea that this could play an important role in the transmission of West Nile virus.”
Irwin said that because nature is so much more complex than a lab, light might not have as profound an effect in the wild. That’s particularly true because the control group was kept entirely in the dark at night, conditions not easily found anywhere in the Chicago area. Still, he hopes additional studies, ideally outside, are performed.
“I could envision somebody going into the city and looking at what you find with sparrows who are living in a parking garage, for example, and those who are still in the city, but maybe at a forest preserve where there is less light pollution,” he said.
Across Chicago, LED lights are being installed to replace more than a quarter of a million highpressure sodium light fixtures in use since the 1970s – a move that could exacerbate the dangers of West Nile virus infection by making light pollution worse, experts said. The city says light pollution will be reduced.
The change from highpressure sodium to LED lights will boost energy efficiency by about 50 percent and drop the electricity expenditure for streetlights from $18 million in 2017 to about $10 million annually once the entire conversion is complete, said Chicago Department of Transportation spokesman Michael Claffey. The city also can expect a total rebate of roughly $35 million from Comed, which offers an incentive for each light converted to LED.
CDOT also said light pollution will decrease with the new lights.
“The LED fixtures we are using are designed to focus light downwards on streets and sidewalks, limiting light trespass into people’s homes and the night sky,” Claffey wrote in an email. “As a result, we are confident that the conversion is reducing light pollution in Chicago.”
Some experts on birds and the night sky, including Kernbach, disagree with that assessment.
When the city began considering new streetlights, LED lights only came with bright white bulbs that gave off a cooltoned blue light. That blue-toned light has since been making headlines as the sleep-depriving culprit in phone and computer screens, Kernbach said.
Less stark LED lights will be used in Chicago, but critics say that because they’re still cooltoned they’ll emit blue light. The city’s current high-pressure sodium lights give off an orange glow that is considered less harmful, even if some people have always hated the color.