FORT WORTH -- To kill mosquitoes carrying West Nile virus, parts of the 76104 and 76110 ZIP codes south of downtown will be sprayed from ground level with the insecticide permethrin Friday, Saturday and Sunday nights, city officials said Wednesday.
"This became a critical area yesterday afternoon," said Brandon Bennett, Fort Worth's code compliance director. "There were a number of human cases that occurred there over a brief period of time."
The area extends south from Vickery Boulevard on the near south side to about Arlington Street in the Fairmount neighborhood. The eastern edge is roughly the BNSF tracks along Interstate 35W; the west edge is about Ninth Avenue in the Medical District.
Contractors will spray along targeted streets three nights in a row, Bennett said.
The effectiveness of ground spraying will be evaluated before aerial spraying is attempted, he said.
The city quickly arranged for a public hearing Wednesday night at the Botanic Garden lecture hall to explain the program and answer questions.
"They are spraying in an area with five hospitals and a birthing center," said Danny O'Brien, who said he has lived in the 76104 ZIP code for more than 30 years.
"Hospitals don't have a day or night. Babies are always born in the middle of the night. Pregnant mothers bring their sick children into hospitals at all hours. How are they going to keep those people safe?"
Permethrin dissipates quickly after its release, is not absorbed easily by the skin, is widely used by homeowners and poses no risks to children or the unborn, officials said.
Affected residents will learn about the spraying schedule through door-to-door notification and community meetings.
Spraying will be between 10 p.m. and 4 a.m. Friday, Saturday and Sunday. If it rains Friday night, the schedule will be pushed to Saturday, Sunday and Monday nights.
"They will probably not spray at all in the rain," said David Jefferson, Tarrant County public health environmental manager.
Other cities in Tarrant County doing ground-level spraying include Benbrook, Euless, Grand Prairie, Hurst, North Richland Hills and Westover Hills.
As of Wednesday, Tarrant County health officials reported two deaths related to the West Nile virus and 181 human cases, up from 171 cases logged Tuesday and 159 cases reported Monday.
Dallas County reported 10 deaths and 207 human cases as of Tuesday. Denton County has reported one death and 86 cases.
State health department statistics show 381 cases and 16 deaths statewide.
Emergency in Dallas
Also Wednesday, Dallas Mayor Mike Rawlings declared a state of emergency and authorized the first aerial spraying of insecticide in the city in more than 45 years. Dallas last had aerial spraying in 1966, when more than a dozen deaths were blamed on encephalitis.
Dallas County officials authorized aerial spraying last week.
"The number of cases, the number of deaths are remarkable, and we need to sit up and take notice," Rawlings said. "We do have a serious problem right now."
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.
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 action beyond seven days.
State Health Commissioner 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 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."
For Fort Worth, Bennett said: "If the need arises aerial spraying is something we might want to look at. We don't want to scratch off a potentially useful tool that we might want to look at down the road."
Low risk from chemical
The concentration of insecticide that will be sprayed is less than in over-the-counter products that are readily available and commonly used by the public. The risk to humans and pets is very low, said Mike Merchant, urban entomologist with the Texas AgriLife Extension Service.
"The nice thing about these sprays is that they are very toxic to mosquitoes at very low dose rates," Merchant said.
"There is a risk of killing some beneficial insects with these sprays. The risk to honeybees is real. But beekeepers can cover their hives at night and the risk to the bees should be very low. If there is an impact on other insects, it will be temporary. There is no evidence that there are any lasting effects to the environment with these sprays."
The rains that pelted the area Wednesday and that were forecast for later in the week spelled both good and bad news in the fight against the mosquitoes.
"The rains will wash out our sewer, storm-water and creek systems, so the mosquitoes breeding at those sites have been washed away and will die," Merchant said.
"The bad news is that the rain will create a whole new set of breeding sites that we will have to be aware of."
This report includes material from The Associated Press.