On a Friday afternoon in late September, Kalamazoo County Health Officer Jim Rutherford announced that aircraft would mist much of the county with an insecticidal spray. Intended to kill mosquitoes, the emergency plan quickly turned into a public relations battle. Hundreds of calls and emails — and even some threats — streamed into Rutherford’s office in southwest Michigan, many expressing concern about the spray.

In the United States, an average of seven human cases of eastern equine encephalitis (EEE) are reported annually, according to the Centers for Disease Control and Prevention. But 2019 has been an especially bad year for the mosquito-borne virus, with at least 35 cases and 13 deaths reported nationwide. In Kalamazoo County, when Rutherford made his decision, EEE had killed a 64-year-old man and sent a 14-year-old girl into intensive care. Faced with the prospect of several more weeks of mosquito-friendly weather, Michigan state officials had offered 15 counties the option of spraying. All of them accepted.