During the daytime hours streetlights and other forms of public lighting are obviously not necessary. But at night entire cities become illuminated with artificial light. This artificial light is known as “light pollution”. Light pollution, as the term suggests, has a negative effect on the earth’s ecosystems. For most of Earth’s history, only the moon and stars provided illumination during the night. Earth’s ecosystems function in accordance with these natural sources of light during the night. Today, natural light competes with artificial light during the night. Multiple studies have shown that artificial light is damaging to the world’s ecosystems and even human health in multiple ways. Now scientists have found conclusive evidence suggesting that light pollution contributes to the spread of the West Nile virus.
According to Jenny Ouyang, an integrative physiologist at the University of Nevada in Reno, light pollution can increase the spread of the West Nile virus. Artificial light during the night is stressful on birds. Light pollution increases levels of certain stress hormones in birds, such as corticosteroids. The stress that birds suffer as a result of light pollution has an impact on their health. Birds, much like humans, experience decreased immune functioning during times of stress. Therefore a bird’s immune system does not function optimally when fighting disease under stress.
Birds are particularly susceptible to West Nile. Mosquitoes that suck blood from West Nile diseased birds can then transfer the disease to humans. One particular study showed that birds exposed to light pollution were unable to fight-off the West Nile virus as well as birds that were not exposed to light pollution. Specifically, birds that are stressed as a result of light pollution-exposure carry the West Nile virus for longer periods of time. After two days, birds that are exposed to natural darkness manage to fight-off West Nile infection within two days on average. However, birds that are exposed to light pollution remain diseased for at least four days. This increased duration of West Nile illness among birds could double the number of infected mosquitoes in the environment. This would obviously result in higher human West Nile infection rates as well. When considering light pollution, humans contribute indirectly to increased rates of the West Nile virus in the human population.