Mosquitoes infected with West Nile virus are doing a lot of damage in Texas, where the death toll from the disease has climbed to 26. There have been 18 deaths reported in Dallas County alone—by far the most in one region in the country. This year the Centers for Disease Control and Prevention has confirmed 1,100 cases of the disease in the U.S. through mid-August, making it the largest-ever West Nile outbreak in the nation. Last week, the outbreak in Dallas prompted the first aerial spraying of insecticide in the city in nearly 40 years. And Houston is to begin aerial spraying as well, as the city’s health officials reported their second and third West Nile deaths this year.