Federal health officials say the current West Nile outbreak is one of the largest in the U.S., with four times the usual number of cases for this time of year.
So far, 1,118 illnesses have been reported, about half of them in Texas. That's the most ever by this time of year according to health officials. Normally, fewer than 300 cases are reported by mid-August. There have also been 41 deaths this year, the Centers for Disease Control and Prevention says.
Cases seem to be accelerating, with about 400 of the cases reported in the last week.
Experts think the mild winter, early spring and very hot summer helped stimulate mosquito breeding and the spread of the virus.