Sunday, January 20, 2019

West Nile Virus to Continue Circulating in Maricopa County, Arizona


First isolated in the West Nile District of Uganda in 1937, the West Nile Virus (WNV) was imported to the USA in 1999,  generating an outbreak that would last 11 years later. A member of the Flaviviridae family, WNV infects humans mostly through mosquito vectors which are in turn infected by feeding on birds that have the virus circulating in their blood.

After first appearing in New York in 1999, the virus appeared in Maricopa county, which houses the Phoenix metropolitan area four years later in 2003. Scientists suggest that the increase in milder winters in the county allow snowbirds and other avian species that carry the virus along with infected mosquitoes to survive and act as virus reservoirs. Thus as the weather warms up, they generate waves of infections as the winter season ends. In 2017, there were 110 cases of WNV infections in Arizona, and the virus existed in 221 mosquito pools in Phoenix.

The strain of WNV in the county appears to be endemic to the area, rather than repeatedly imported, having been circulating in Maricopa for the last seven years. In 2017, the same strain has also been reported in southern California and southwestern Utah.

Most people with the virus do not realize that they are infected, with signs and symptoms mirroring the flu, such as nausea, vomiting, fever and headaches. A small fraction of people infected can develop serious conditions including paralysis, meningitis and encephalitis, and those aged 50 years and older are at a higher risk of infection.

-Riasoya Jodah



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