In many places, a moonless night sky is no longer totally black. Artificial lighting can give the night a lasting light. This so-called light pollution can affect animals. Even moderate light pollution, a new study finds, can roughly double how long a house sparrow infected with West Nile Virus (WNV) remains at high risk of spreading disease. If bitten by a mosquito, that virus can now spread to other animals, including people.
"In the United States, house sparrows are about as widespread as artificial lighting. So they made a useful test species in a new first-of-its-kind study," says Meredith Kernbach. Her team used these birds to test whether light at night might affect the spread of the West Nile Virus.
Kernbach based much of her lab test on real-world conditions. In the study, some house sparrows in the lab spent the night in an area that was dimly (昏暗地) lit. These birds were slower in fighting off West Nile Virus infections than those that spent the night in full darkness.
WNV needs a mosquito to spread from bird to bird, or from bird to human. If a mosquito doesn't pick up enough viruses from the blood of an infected animal, its new victim might be able to avoid getting sick. House sparrows kept under a dim night light typically had enough viruses in their blood to be a source of virus for at least four days, Kernbach reports. House sparrows in full darkness had enough viruses to spread the disease only for two days.
What light does to the birds is only part of the story, points out Davide Dominon, a physiologist at the Nether-lands Institute of Ecology in Wageningen. "Researchers will need to look for effects on the virus itself," he says. "And, of course, on the mosquitoes."
