Since the first human West Nile virus (WNV) cases were reported in Arizona in 2003 and through 2020, the state reported a total of 1,939 cases, including a single year high of 391 in 2004.
Arizona state health officials as of yesterday reported 1,567 total WNV cases (confirmed and probable) in 2021. The vast majority (85%) of the cases were reported from Maricopa County (1339), according to the most recent data.
In addition, 110 deaths were reported statewide due to WNV in 2021, well more than half the total WNV deaths reported nationally.
Beside Maricopa County, Pinal and Pima counties reported 120 and 94 total cases, respectively.
Why the surge in 2021? One explanation is 2021 had a particularly wet summer that followed an extraordinarily dry summer in 2020. In addition, warmer-than-usual temperatures that extended through November and into early December kept the mosquito season going later than usual.
WNV is a disease caused by a virus that is spread through mosquito bites. WNV is found on every continent except Antarctica. It was first detected in North America in 1999, and has since spread across the continental United States and Canada.
It takes 2-6 days for a person to develop symptoms after being bitten by a mosquito infected with WNV.
Only 1 out of 5 people with WNV will have symptoms. Individuals may develop a fever with other symptoms, such as headache, body aches, joint pains, vomiting, diarrhea, or rash. Most people who experience these symptoms will recover completely, although fatigue and weakness can last for weeks or months.
Severe illness can occur in people at any age; however, people over 60 years of age are at the greatest risk for severe illness. Additionally, individuals with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and people who have received organ transplants are also at greater risk for serious illness. In more severe cases, the illness can affect the brain causing encephalitis (swelling of the brain) or meningitis (swelling of the surrounding brain tissues). The symptoms of neurologic illness can include headache, high fever, neck stiffness, disorientation, coma, tremors, seizures, or paralysis. Recovery from severe illness may take several weeks or months and some of the neurologic problems may be permanent. Rarely, death can occur.
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