Climate change may lead to outbreaks of West Nile virus, which can cause fatal neurological diseases, in Southern California, according to a UC Berkeley-led study published Wednesday.
The research found an increase in West Nile transmission in areas with higher temperatures, posing a threat to previously less-affected areas. Because of increased temperatures as the planet warms, regions closer to the coast are likely to face an increased risk of West Nile virus outbreaks, according to study lead author Nicholas Skaff.
When West Nile virus positively infects someone, it can result in West Nile fever, which poses less of a threat, or West Nile neuroinvasive disease, which can lead to death or neurological damage. According to co-author Christopher Hoover, more than 80% of people who get West Nile virus are asymptomatic or have few symptoms.
“West Nile virus has been a major public health issue in California, especially in the Los Angeles metro area, since it emerged in the state in 2003,” Skaff said in an email. “We wanted to do our best to help understand and anticipate outbreaks so that public health officials, mosquito control professionals and the general public can be prepared.”
Skaff added that the goal of the study was to investigate the reasons behind “somewhat unpredictable” patterns of West Nile virus transmission.
The study used machine learning to analyze infection rates of West Nile virus using mosquito surveillance data conducted independently between 2006 to 2016, said study co-author Philip Collender.
While the research shows a clear connection between temperature and transmission, this relationship is not a linear one, instead forming more of an “S” shape.
Temperatures below 70 degrees Fahrenheit tend to suppress infection, but as temperatures rise from 70 to about 73 degrees Fahrenheit, the risk of West Nile virus transmission increases greatly. This increase stabilizes, however, as temperatures get warmer than 73 degrees Fahrenheit.
“It serves as a bit of a warning to people in those areas in and around LA, where we are going to see these more frequently warmer temperatures,” Hoover said. “We can respond and preempt this increase in transmission doing classic disease mitigation things for (mosquito)-borne diseases like West Nile virus.”
Hoover suggested spraying for mosquitoes, preventing standing water and reporting dead birds or large mosquito populations to mitigate transmission.
The findings from this research will potentially allow scientists to predict summers of intense transmission depending on temperature, according to Skaff.
“The effects of climate change on human health are vast and varied,” Hoover said. “We expect warmer temperatures and changing landscapes, and those sorts of things are going to affect human health in the not-too-distant future.”