Environment & Science

Study: West Nile virus cases likely to increase in Calif.

The Aedes albopictus mosquito, also known as the Asian Tiger Mosquito, has been found to spread West Nile Virus.
The Aedes albopictus mosquito, also known as the Asian Tiger Mosquito, has been found to spread West Nile Virus.
James Gathany/Centers for Disease Control and Prevention

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As the planet warms due to climate change, instances of West Nile virus will increase across the continent and spread into areas previously considered unsuitable for the virus’s propagation, according to a UCLA study published Thursday in the journal Global Change Biology.

“With climate change, we’re seeing what was once thought of as tropical diseases moving into much more temperate areas,” said Ryan Harrigan, lead author of the study and a postdoctoral researcher at the Center for Tropical Research at UCLA’s Institute of the Environment and Sustainability.

Researchers took nine years of West Nile virus infection data across the country from 2003 – 2011 . They examined how it correlated with temperature and precipitation levels. They then developed a suite of models to predict what the spread of the virus will likely look like in the future.

The researchers said their models were able to predict accurately for 2012 areas where human infections had significantly higher probability of occurring. Looking forward to 2050 and 2080, researchers found that the disease will be able to propagate in areas that today seem too cold.

“What we see is a massive northward expansion of the disease and possible range of the virus well into the northern latitudes in Canada,” Harrigan said.

He said that the spread could have a debilitating impact on native species.

“This is concerning because there is native wildlife there that has not been previously exposed to the disease and that would suffer likely dramatic population declines, given the introduction of a brand new disease,“ Harrigan said.

California had nearly 500 cases of human infections by West Nile virus in 2012, the second-highest number behind Texas. Harrigan said the models show that number could increase in the future.

“Seventy two percent of the state is expected to, by area, increase in probability of West Nile presence by the year 2080,” he said.

The study shows where West Nile virus could have increased probability of occurrence. Harrigan said that actual numbers of human cases is hard to predict, as regional measures such as mosquito control can have a large impact on disease prevalence.

Those control methods may become more important as more areas become viable breeding grounds for the disease.

“We don’t have West Nile virus in Alaska yet,” Harrigan said. “But under our model and predictions of climate change, you would expect that in the very near future, if not already, the conditions are favorable for West Nile transmission in Alaska.”