Warming climate to shift threat of West Nile virus in the U.S.

Sept. 15 (UPI) — West Nile virus spreads most rapidly in places featuring average temperatures between 75 and 77 degrees Fahrenheit.

According to a new model, as the climate warms, West Nile virus transmission is likely to increase in some parts of the United States, while the threat dissipates in others.

“As the climate warms, it is critical to understand how temperature changes will affect the transmission of mosquito-borne diseases,” lead researcher Marta Shocket said in a news release.

Shocket is now a postdoctoral researcher at UCLA, but conducted the new research while a fellow at Stanford.

For the new study, the results of which were published Tuesday in the journal eLife, researchers modeled how temperature changes will influence the range of three U.S. mosquito species.

The three species are responsible for the spread of six mosquito-borne viruses, including the West Nile, St. Louis Encephalitis, Eastern and Western Equine Encephalitis, Sindbis and Rift Valley fever viruses.

To build the model, scientists relied on lab experiments demonstrating the influence of temperature on each species’ reproduction, development, survival, biting rate and ability to transmit the virus.

“Most of the viruses covered in this work are from more temperate areas than more commonly studied tropical diseases,” Shocket said.

“We compared these results to those of tropical diseases like malaria and dengue and found that the optimal temperatures and cold thermal limits for virus spread are cooler,” she said. “This means the viruses spread more efficiently at cooler temperatures compared to more tropical diseases, as you would expect.”

Another study, published earlier this month in the journal Lancet Planetary Health, showed the threat of some tropical diseases, such as Chikungunya and dengue, are likely to grow as temperatures warm across sub-Saharan Africa.

The latest research suggests the United States is likely to experience similar shifts in viral transmission threats.

Currently, roughly 70 percent of the U.S. population lives in places that are too cold for transmission of West Nile and the other temperate viruses. Around 30 percent live in places that get too hot during the summer for the spread of West Nile.

The new research showed that places that already get too hot in the summer for viral transmission are likely to see fewer cases of West Nile as temperatures continue to rise.

However, models showed higher temperatures will likely increase the threat of mosquito-borne viruses across sizable portions of the country. The simulations suggest rising temperatures will also extend the season for mosquito-borne virus transmission into the fall and spring.

“Climate change is poised to increase the transmission of West Nile and other mosquito-borne viruses in much of the U.S.,” said senior author Erin Mordecai, assistant professor of biology at Stanford.

“But these diseases also depend on human contact with mosquitoes that also contact wildlife, so factors like human land use, mosquito control, mosquito and virus adaptations, and the emergence of new viruses make predicting the future of mosquito-borne disease a challenge,” Mordecai said.