Light pollution may increase risk of West Nile virus jumping from birds to humans

July 24 (UPI) -- The risk of West Nile virus spreading among animal populations and making the jump from birds to humans may be greater in areas with light pollution, a new study found.

Though mosquitoes are the primary vector for West Nile virus, the virus is common among house sparrows. Infected house sparrows can spread the disease to humans.

Through a series of lab tests on captive house sparrows, scientists found birds exposed to artificial light at night -- levels comparable to the amount of light used in parking lots -- carried larger viral loads for longer than birds that spent their nights in the dark. Birds exposed to artificial light carried the virus for up to two days longer than unexposed birds.

Larger, persistent viral loads increase the odds that the virus will spread to other vectors, researchers determined. When scientists plugged their findings into a model designed to simulate the risk of disease outbreaks, researchers found light pollution increased the potential for a West Nile virus outbreak by 41 percent.

"The findings may be the first indication that light pollution can affect the spread of zoonotic diseases," Meredith Kernbach, postdoctoral student in the University of South Florida College of Public Health, said in a news release. "Many hosts and vectors use light cues to coordinate daily and seasonal rhythms, which is among the most reliable environmental cues, and disruption of these rhythms by light exposure at night could affect immune responses, generating the effects we see here."

Researchers decided to test house sparrows because the birds are common all over the world and live in close proximity to humans. Despite the prolonged infection, birds exposed to light pollution were not more likely to die.

Scientists shared the results of their study this week in the journal Proceedings of the Royal Society B: Biological Sciences.