ALAN May Be Increasing West Nile Virus Spillover from Wild Birds

The study published in Proceedings of the Royal Society B concludes infected house sparrows living in light polluted conditions remain infectious for two days longer than those who do not, enhancing their host competence, or propensity to generate infection in other hosts or vectors. In turn, mathematical models show this likely increases the potential for a WNV outbreak by about 41 percent.

Original Abstract of the Publication in the
Proceedings of the Royal Society B:
Among the many anthropogenic changes that impact humans and wildlife, one of the most pervasive but least understood is light pollution. Although detrimental physiological and behavioural effects resulting from exposure to light at night are widely appreciated, the impacts of light pollution on infectious disease risk have not been studied. Here, we demonstrate that artificial light at night (ALAN) extends the infectious-to-vector period of the house sparrow (Passer domesticus), an urban-dwelling avian reservoir host of West Nile virus (WNV). Sparrows exposed to ALAN maintained transmissible viral titres for 2 days longer than controls but did not experience greater WNV-induced mortality during this window. Transcriptionally, ALAN altered the expression of gene regulatory networks including key hubs (OASL, PLBD1 and TRAP1) and effector genes known to affect WNV dissemination (SOCS). Despite mounting anti-viral immune responses earlier, transcriptomic signatures indicated that ALAN-exposed individuals probably experienced pathogen-induced damage and immunopathology, potentially due to evasion of immune effectors. A simple mathematical modelling exercise indicated that ALAN-induced increases of host infectious-to-vector period could increase WNV outbreak potential by approximately 41%. ALAN probably affects other host and vector traits relevant to transmission, and additional research is needed to advise the management of zoonotic diseases in light-polluted areas.

"The findings may be the first indication that light pollution can affect the spread of zoonotic diseases," said lead author Meredith Kernbach, PhD student in the University of South Florida College of Public Health. "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 studied 45 house sparrows, exposing half to artificial light at night. Following 7-25 days in captivity, the team exposed the birds to WNV and took blood samples 2, 4, 6, and 10 days post-exposure. Researchers found all birds were infected within 2-4 days, however after that, birds exposed to light at night maintained transmissible burdens of WNV.

Kernbach says they picked the little brown birds since they live in close proximity to humans in urban areas, play host to a number of parasites and diseases, and are frequent carriers of WNV. While birds exposed to light pollution remain infected for a longer period of time, this did not increase mortality rates.

These results follow a previous study led by the University of South Florida that found zebra finches that have the avian stress hormone corticosterone (CORT) are more susceptible to mosquito bites. Such stress is known to be caused by a number of factors such as road noise, pesticides and light pollution. Researchers suggest new lighting technologies be created that are detectable to humans, but not for wildlife.

References:

Meredith E. Kernbach et al, Light pollution increases West Nile virus competence of a ubiquitous passerine reservoir species, Proceedings of the Royal Society B: Biological Sciences (2019). Published: 24 July 2019. DOI: 10.1098/rspb.2019.1051