West Nile virus cases could set a NC record in 2022. Is it tied to climate change?

An exotic mosquito-borne virus that first emerged on this side of the Atlantic at the turn of the century could set a record number of infections in North Carolina this year, with health officials warning it could be a harbinger of things to come as climate change promises warmer temperatures.

State health officials have recorded 10 cases of West Nile Virus and 2 fatalities so far this year, with several weeks of warm weather left likely to mean more infections could be percolating. Positive cases have been reported in − among others − New Hanover, Cumberland, Wake, Mecklenburg, and Catawba counties, with both fatalities in Cumberland County.

"Once a mosquito is infected with West Nile, it can continue to infect people," said Michael Doyle, the state public health entomologist. "And the longer it stays warm, the longer the mosquito bites."

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Since 1999, North Carolina generally averages just a handful of cases a year, although it did record 10 in 2018.

Prime infection season runs from early summer through fall, which ends on Dec. 20.

The U.S. Centers for Disease Control and Prevention (CDC) says West Nile is the leading mosquito-borne disease in the country and has no vaccine. While most people infected with the virus don't feel sick, about 20% of those infected develop a fever or other symptoms, such as body aches, a rash, vomiting, or diarrhea. About one in 150 infected people develop a serious, sometimes fatal illness, including inflammation of the brain, according to the CDC.

While 10 cases isn't a huge number, it's what it could mean about future mosquito-borne disease outbreaks as climate change creates a more inviting habitat in North Carolina that has officials concerned.

"This is going to be a growing problem," said Dr. Michael Reiskind, an entomologist at N.C. State University.

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According to a U.S. Environmental Protection Agency seasonality report published in late 2021, all seasons have warmed in the U.S., with winter temperatures increasing by nearly 3 degrees Fahrenheit since 1896.

The National Oceanic and Atmospheric Administration (NOAA) reports that temperatures in North Carolina have risen more than 1 degree Fahrenheit since 1900.

"Under a higher emissions pathway, historically unprecedented warming is projected this century," states the agency's 2022 climate summary for North Carolina.

Climatologists have warned that cuts in greenhouse gas emissions promised by governments and big businesses in recent years won't be enough to stop a dramatic increase in temperatures well beyond the goal of keeping the warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) by the end of the century.

With West Nile just one of several viruses on their radar screens, Doyle said health officials are preparing for a rise in mosquito-borne illnesses in coming years.

"We expect it," he said. "The primary concern we have is can we adapt to it."

Viruses on the move

While a number of factors are at play as to how much and how quickly a problem develops, Reiskind said viruses are very adaptable and transportable.

There's always been the fear among health officials of a traveler bringing an exotic disease into the country that he or she caught while overseas. What climate change could make more likely is the local transmission of an exotic ailment as viruses found in warmer climates find previously cooler areas more to their liking. And with a reservoir of mosquitoes or other insects already here or also moving into new habitats, officials warn that's not a good combination.

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Reiskind said there are 60 species of mosquitoes in North Carolina, with a half-dozen or so considered non-native and not likely found in the Tar Heel State a century ago.

Recent outbreaks of mosquito-borne illnesses moving around the world include the infamous Zika outbreak last decade in Central and South America, leading to babies being born with serious birth defects. Outbreaks of dengue fever in the continental United States, long a rarity, are also becoming more common, especially in Florida and areas near the Rio Grande.

But a lot about how quickly an outbreak could ramp up isn't known, especially since there are so many variables involved. Reiskind said his lab is studying whether it's the abundance of general mosquito numbers or a specific species that's more likely to lead to an uptick in virus cases. 

Rising threat

While the rise in West Nile cases is worrisome, health officials said the virus in its short time circulating in the United States has generally been found to ebb and flow, with one year a high number of infections followed by several years of lower numbers.

Officials said that's probably because the bird population, which is the primary focus of the virus, develop immunity to West Nile.

"What would really worry us is if cases stayed high for a number of years," said Dr. Helen Lazear, a virologist at the University of North Carolina at Chapel Hill.

Climate change also might not just mean more mosquitoes, but potentially an extended infection season for West Nile. Doyle, the state entomologist, said while vector-borne viruses have a "favorite" mosquito they like to partner with, they also have certain weather conditions they like to thrive in. For West Nile, that's the cycle of heavy rains followed by extended dry conditions − the very weather pattern climatologists warn North Carolina is likely to see in coming decades, and to some degree is already starting to experience.

Much of Eastern North Carolina was in drought for nearly nine months starting in October 2021, only emerging out of the dry spell this summer. The cycle could be repeating itself, with the National Weather Service in Wilmington reporting this week that the Port City is facing a 15-inch rain deficit for the year.

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 Doyle also warned that controlling viruses is challenging because, well, they are viruses.

“Viruses adapt, just like COVID did," Doyle said. "So the West Nile we have now is not what came here in 1999."

That doesn't mean officials and individuals can't be pro-active, though.

Malaria and dengue fever were largely eradicated from the U.S. last century because of aggressive anti-mosquito measures along with increased sanitary practices, like the rise of indoor plumbing. Educational outreach efforts warning about using repellants, limiting times outside at dusk and dawn, and the dangers posed by standing water also have helped control the insects.

To supplement individual efforts many Southern communities also have aggressive vector-control methods, including treating mosquito breeding sites and spraying.

But Doyle said that outside of Eastern North Carolina spraying isn't universally practiced − or loved.

“But when there’s an outbreak, it’s kind of like going into the emergency room because there are more serious measures that are needed, at least in the short term," he said.

Doyle said as our weather warms, it's only logical to assume that it will expand the opportunities for disease transmission by mosquitoes. And that means we will likely have to change our approach to meet the new threat.

“How much will the threat increase?" he said. "We don’t know, but that will be determined by how much our climate changes."

Reporter Gareth McGrath can be reached at GMcGrath@Gannett.com or @GarethMcGrathSN on Twitter. This story was produced with financial support from 1Earth Fund and the Prentice Foundation. The USA TODAY Network maintains full editorial control of the work.