Study: West Nile virus appears endemic in Maricopa County

A new study suggests that a strain of West Nile virus will remain in the most populous county of Arizona in the near future.

Arizona researchers have said that the same mild winters that brought the snowbirds to Maricopa County also allowed mosquitoes and some virus-carrying birds to survive in winter in order to spread West Nile again when the weather is warming up.

The Phoenix KJZZ radio station reports that the study concludes that the potentially deadly virus appears to be endemic to the county that includes the Phoenix metropolitan area.

Experts say West Nile is the main source of mosquito-borne diseases in the United States. The virus entered the country for the first time in 1999 in New York and was reportedly detected in Maricopa County four years later.

West Nile is transmitted to humans by the bite of an infected mosquito.

According to the authorities, about 20% of people infected with the virus will experience symptoms similar to those of the flu within 3 to 15 days of a mosquito bite. Fever, headache, nausea, vomiting, swelling of the lymph nodes and rash may be symptoms.

A small percentage of people infected with West Nile virus could die or suffer serious symptoms such as meningitis, encephalitis or paralysis. People over 50 usually have a higher risk of developing severe symptoms.

There were 110 confirmed or probable cases of West Nile in Arizona in 2017 and environmental services from the Maricopa County Vector Control District found the virus in 221 mosquito pools in the Phoenix metropolitan area.

To find out whether it is endemic or repeatedly imported, researchers have developed a new technique for sequencing 14 West Nile genomes in mosquitoes in Maricopa County.

"It's kind of a look at Ancestry.com – we can really understand the relationships between viruses that appear in mosquitoes throughout the West," said David Engelthaler, director of TGen. North to Flagstaff and co-author of the Crystal Hepp study from Northern Arizona University.

Their findings revealed two family lineages, one of which has been circulating in Arizona for at least seven years.

By calculating when different virus strains separate from their common ancestors, researchers could also track their spread.

"In 2017, it appears that the endemic strain of Maricopa County has been exported to southern California and southwestern Utah," Hepp said.

Engelthaler said that "the convergence of events has allowed Maricopa County in some areas to really be not only a hot focus of West Nile, but a long-term source, now that it seems really endemic in this region".

The study was primarily supported by the Arizona Biomedical Research Committee and the Arizona Board of Regents Technology Research Infrastructure Fund.