County officials have confirmed the presence of the West Nile virus for the first time this season.
Maricopa County Environmental Services workers reported an increased number of mosquitoes showing up in traps, with one sample testing positive for the virus.
The department monitors more than 750 traps each week placed in sites known to be frequent mosquito breeding areas.
West Nile is one of several mosquito-transmitted illnesses present in the Valley, which appears in the summer and lasts through the fall.
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About 70-80 percent of those infected never experience symptoms, according to Maricopa County Public Health. Of those who do have symptoms, the most common are fever, aches, joint pain and vomiting. In rare cases, the virus can lead to neurologic illnesses such as meningitis or encephalitis.
So far this year, Maricopa County health officials have not received lab confirmation of any human cases of West Nile infection.
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