The West Nile virus is making its annual visit to Arizona.  We’ve had several cases now in Arizona (and 1 death) – mostly from the East Valley in Maricopa and Pinal Counties. Most of these cases have the more severe form of West Nile virus which causes meningitis or encephalitis.  We rarely hear of most cases because people with milder symptoms of West Nile stay at home and don’t seek medical care.  That means there are a lot more people sick with West Nile than we know about.  So far this year, over 120 mosquito samples have tested positive for West Nile virus all over the state, although many have been in the East Valley.

West Nile virus can cause severe illness in people but only about 20% of those infected get flu-like symptoms like fever, headache, body aches and muscle weakness. Some people, especially the elderly, may get more severe symptoms like high fever, severe headache, neck stiffness, and/or encephalitis or inflammation of the brain.

The virus mostly goes back and forth between mosquitoes and birds (the mosquito’s blood of choice), but when an infected female mosquito bites a person, the person can get West Nile.  Prior to 1999, the virus was endemic in the Middle East, Africa, much of Asia and parts of Europe.  It first showed up on the US East Coast in 1999.  Every summer it traveled a little farther west- first reaching Arizona in the late 2003.  2004 was our worst summer for the virus because most of the Arizona birds were susceptible and it spread like wildfire that spring and summer.  While we expect the virus to come back every summer in Arizona, we don’t ever expect to have one like 2004 because most of our urban birds have antibodies now.  However we could have 100 or more cases this year based on the fact that we have more than a dozen cases this early in the summer. You can see our prevention messaging and tactics at:

By the way…  Maricopa County will be monitoring the Salt River bed over the next few days to make sure that any downstream pools of water that result from the Tempe town lake dam burst are addressed so they don’t breed mosquitoes.