Fort Worth is preparing for additional ground spraying, and Denton County public health officials are seeking state help for aerial spraying in an escalation of attacks on mosquitoes that carry the West Nile virus.
Mansfield will begin ground spraying at the end of the week, the city announced Wednesday.
Meanwhile in Atlanta, the federal Centers for Disease Control and Prevention said that never before have so many West Nile cases been reported this early -- four times the usual number.
"We're in the midst of one of the largest West Nile outbreaks ever seen in the United States," said Dr. Lyle Petersen, who oversees the CDC's mosquito-borne illness programs.
It's still too early to say how bad the year will end up because most infections are reported in August and September.
So far, 1,118 illnesses have been reported in 38 states, about half of them in Texas. In an average year, fewer than 300 cases are reported by mid-August. There have also been 41 deaths this year, the CDC said.
And cases seem to be accelerating: About 400 were reported in just the last week.
Experts think the mild winter, early spring and very hot summer helped stimulate mosquito breeding and the spread of the virus. Mosquitoes pick up the virus from birds they bite, then pass it on to people.
CDC officials are also looking into the possibility that the virus mutated, but they have no concrete evidence, Petersen said.
West Nile virus was first diagnosed in Uganda in 1937, but no U.S. cases were reported until 1999 in New York. The virus gradually spread across the country. It peaked in 2002 and 2003, when severe illnesses reached nearly 3,000 and deaths surpassed 260. Last year was mild, with fewer than 700 cases.
Extending the spray zone
Tarrant County has reported 218 cases and four deaths as of Wednesday.
In far north Fort Worth in parts of the 76137 ZIP code, contractors will spray about 40 linear miles of streets beginning Friday, officials said Wednesday.
Data received from Tarrant County Public Health on Wednesday afternoon indicated new positive mosquito pools in the area. And new human cases of the virus warranted an extension of the ground-spraying program, said Brandon Bennett, Fort Worth code compliance director.
"We had at least three different human cases of West Nile virus infections in this area within the past week," Bennett said.
Today, city staffers are scheduled to go door to door to inform residents and business owners of the plan. On Friday, workers will tell residents and business owners just outside the spray zone, Bennett said.
Weather permitting, spraying will occur from 10 p.m. to 4 a.m. Friday, Saturday and Sunday, Bennett said. The area has more greenbelt components than the last area that was sprayed -- the near south side -- and will require contractors to use all-terrain vehicles.
"Regardless of how often we spray or where we spray, we've got to get people to drain the standing water from their yards or else we could face a whole new crop of adult mosquitoes," Bennett said.
5 areas in Mansfield
Mansfield will follow its Metroplex neighbors and begin ground spraying Sunday.
Officials made the decision after finding five confirmed human cases and three mosquito traps that were positive for West Nile virus, storm-water manager Howard Redfearn said.
This is the first time city officials have sprayed since Mansfield instituted a mosquito control policy in 2008, Redfearn said.
Weather permitting, five areas will be sprayed from 9 p.m. to 5 a.m. Sunday through Tuesday, he said. They include downtown; the Remington Ranch/Fox Glen/Vinewood area off South Main Street; Kings Mill; Heritage Estates; and Tanglewood Estates, according to a city news release.
A map of the area is on the city's website -- mansfield-tx.gov.
No deaths in Mansfield are linked to the virus, Redfearn said.
Spraying will cost $15,000, Redfearn said.
Public health emergency
Denton County Judge Mary Horn declared a public health emergency Wednesday, a requirement for the county to request state and federal aid for aerial spraying.
The action came at the request of the county health department.
Denton County has recorded 105 human cases and one death, but the rate of infection, the state's highest, is what concerned officials, said Bob Martinez, the county's public health preparedness coordinator.
"We're seeing a lot of cases come into our hospitals," Martinez said. "We have a little more neuroinvasive disease than some of our neighbors, and that was a factor in our decision."
Ground spraying and the use of larvicide in ponds and standing water have not been enough, Martinez said.
Around the state
On Wednesday, Bexar County health officials reported a 77-year-old San Antonio man as the county's first West Nile-related death.
Dr. Nathan Vincent, assistant director of the Metropolitan Health District, said the man was a military retiree and one of only three West Nile cases diagnosed this year.
In Bowie County, a 70-year-old Texarkana, Texas, woman is the first fatality there, health officials said Wednesday.
Harris County officials reported Tuesday that two more Houston residents have died from the virus, for a total of three.
No deaths have been reported in Harris County outside Houston. But about 63,000 acres of the county were to be sprayed from the air Wednesday night.
Dallas County used aerial spraying in parts of Dallas last week. But it's too soon to measure the effect -- it takes three to 14 days for people to develop symptoms after being infected by a mosquito, officials said.
Staff writer Amanda Rogers contributed to this report, which includes material from The Associated Press.