Dallas Mayor Mike Rawlings on Wednesday declared the city’s recent West Nile virus outbreak to be a state of emergency and authorized the first aerial spraying of insecticide in the city in nearly 40 years.

Dallas and other North Texas cities have agreed to the rare use of aerial spraying from planes to combat the nation’s worst outbreak of West Nile virus so far this year. Dallas last had aerial spraying in 1966, when more than a dozen deaths were blamed on encephalitis.

More than 200 cases of West Nile and 10 deaths linked to the virus have been reported across Dallas County, where officials authorized aerial spraying last week. State health department statistics show 381 cases and 16 deaths related to West Nile statewide.

“The number of cases, the number of deaths are remarkable, and we need to sit up and take notice,” Rawlings said during a city council briefing. “We do have a serious problem right now.”

Aerial spraying for mosquitoes could begin Thursday evening, depending on weather conditions. The state health department, which will pay for the $500,000 aerial spraying with emergency funds, has a contract with national spraying company Clarke. Clarke officials have said two to five planes will be used in Dallas County.

Dallas City Council members voiced concerns about aerial spraying’s health effects on humans and animals. Rawlings said the aerial dosage will be much lower than the dosage used so far during ground spraying. He also said aerial spraying recently has been safely used in California, Massachusetts and New York.

The city charter allows Rawlings to declare a state of emergency and request aerial spraying, but the City Council would have to approve additional action beyond seven days.

State health commissioner Dr. David Lakey, who participated in the briefing via telephone, reiterated the seriousness of the situation in Dallas, saying half of all West Nile cases in the United States so far this year are in Texas.

“There is a public health emergency related to West Nile right now,” Lakey said. “The risk of air-based spraying is minimal versus the ongoing spread of West Nile.”