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Another Reason to Turn Off the Lights

A recent study suggests that artificial lighting makes it harder for birds — and perhaps humans — to fight off West Nile Virus.



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A house sparrow.
  • A house sparrow.

In Alameda County, three different species of mosquitoes have been found this year so far: Culex pipiens, Culex tarsalis, and Culex erythrothorax. These mosquitoes will feed in crepuscular lighting, commonly known as dusk and dawn, or at night. Kernbach says that light pollution will confuse mosquitoes into thinking that it’s sunrise and sunset constantly, meaning longer feeding periods. The Alameda County Public Health Department states that West Nile Virus has generally run from June until November.

But recent drought and deluge cycles in California have exacerbated the temperature-dependent West Nile Virus pathogen. There were record numbers of West Nile Virus-infected birds and mosquitoes — 97 dead birds and 16 groups of mosquitoes — found in Alameda County in 2014, one of the driest years in California on record.

Erika Castillo, regulatory and public affairs director for Alameda County Mosquito Abatement District, said that, previously, mosquito populations were expected to increase during the wet seasons because of their natural tendency to gather around water sources.

But because there have been fewer sources of water during drought seasons, Castillo has observed mosquitoes and birds traveling to and congregating at the same water spots, which encourages even more transmission of West Nile Virus.

So even though West Nile Virus-infected mosquitoes have historically populated warmer regions of Alameda County, like Union City, Hayward, and Livermore, the cooler regions of the county are no longer safe. Mosquito Abatement District lab director Haas-Stapleton also believes this to be the case. “We can define West Nile Virus-infected birds and mosquitoes in warmer habitats, such as those that occur in the southern and eastern parts of Alameda County,” said Haas-Stapleton. “However, we do occasionally find West Nile Virus-infected birds and mosquitoes in the northern parts such as Berkeley and Albany.”

Castillo explained that while the risks of contaminating yourself with a West Nile Virus-infected bird is fairly low, there is still a probable chance of transmission if body fluids are exchanged and breached through the eyes, nose, or mouth.

To combat the problem of light pollution’s link to the spread of infectious diseases, Kernbach suggests switching from the more harmful cool-white and blue lights to warmer-hues of LED night lighting, like the ones that emit warm white, orange, or yellowish hues.

But Barentine advocates for another solution. “What we really have to do is reduce the human demand for light at night,” he said. “Only if we start to eliminate where it’s truly not needed or lower it to appropriate levels, are we going to really start reducing the pressure that’s put on all kinds of species.”

This report was originally published by our sister publication, Oakland Magazine.


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