Light pollution helps West Nile virus spread. (Go figure.)

Science Daily makes a fact-based plea to keep sparrows in the dark – because nighttime lighting makes the birds stay sick with West Nile – and contagious – about twice as long:

House sparrows, about as widespread across the United States as artificial lighting itself, make a useful test species for a first-of-its-kind study of how night illumination might contribute to disease spread, said Meredith Kernbach, an eco-immunologist at the University of South Florida in Tampa. Passer domesticus brought into the lab and kept dimly illuminated at night were slower in fighting off West Nile infections than lab sparrows allowed full darkness, Kernbach reported January 7 at the annual meeting of the Society for Integrative and Comparative Biology.

Sparrows kept under a dim night light typically had enough virus in their bloodstreams for at least four days to turn biting mosquitoes into disease spreaders, she said. Sparrows housed in darkness had high virus concentrations for only about two days. Doubling the time a bird can pass along a big dose of virus could in theory increase the likelihood that a disease will spread.

Kernbach based much of her lab test on real-world conditions. The viral dose she gave the birds was strong enough to kill about 40 percent of them, and it was well within what a mosquito might pick up vampirizing birds or mammals. She used white incandescent lighting, basically the last century’s universal light bulb, which is still common despite inroads by LED lighting.

The white incandescence in the experiment has plenty of warmer tones, but does include some of blue wavelengths from common cool white LEDs, or light-emitting diodes. The sparrows on average experienced about 8 lux of this white incandescence during their seven-hour nights. (A heavily overcast day, by comparison, ranks at about 100 lux.)

Other studies in birds are showing that artificial night lighting can affect concentrations of the hormone corticosterone, which helps orchestrate reactions of the immune system.