PHOENIX – A new study suggests that it is going to remain in Arizona's most populous county for the foreseeable future.
Arizona researchers say the same mild winters that bring snowbirds to Maricopa County also let mosquitoes and certain virus-reservoir birds survive
Phoenix radio station KJZZ reports the study concludes that potentially deadly virus appears to be endemic to the county which includes the Phoenix metro area.
Experts say the West is the foremost source of mosquito-borne disease in the U.S. The virus reportedly first entered the country in 1999 in New York City and was detected in Maricopa County four years later.
West Nile is transmitted to humans by the bite of an infected mosquito.
Authorities say 20% of people infected with virus will feel flu-like symptoms within 3 to 15 days after the mosquito bite. Symptoms may include fever, headache, nausea, vomiting, swollen lymph glands and skin rash.
A small percentage of those infected with West Nile could have suffered severe symptoms such as meningitis, encephalitis or paralysis. Persons over age 50
The Nile in Arizona in 2017 and the Vector Control District of the Maricopa County Environmental Services found the virus in 221 mosquito pools in the Phoenix metro.
To find out if it is endemic or repeatedly imported, the researchers developed a new technique for sequencing 14 West Nile genomes in mosquitoes across Maricopa County.
"We can really understand the relationship between the viruses that are showing up in the mosquitoes throughout the West," said David Engelthaler, director of TGen North in Flagstaff and co-author of the study with Crystal Hepp of Northern Arizona University.
Their results turned up two family lines, one of which has been circulating in Arizona for at least seven years.
By calculating when different viral strains broke off from their common ancestors, researchers also could track their spread.
"In 2017, it looks like the strain that was endemic to Maricopa County was exported to southern California and to southwestern Utah," Hepp said.
Westmile, a long-term source of it, is now about the end of the day.
The study was backed by the Arizona Biomedical Research Committee and the Arizona Board of Regents' Technology Research Infrastructure Fund.
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