The flooded home and pool of Maurice and Jenny Teixeira is shown following the aftermath of tropical storm Harvey on the west side of Houston, Texas, U.S., September 7, 2017. Reuters/Mike Blake HOUSTON (Reuters) - Texas has launched aerial attacks on mosquitoes swarming coastal regions of the state and threatening to spread disease and hinder disaster recovery in the aftermath of Hurricane Harvey.

U.S. Air Force C-130 cargo planes began spraying insecticides over three eastern Texas counties over the weekend and will expand to other areas over the next two weeks, officials from the Texas Department of State Health Services (DSHS) said.

About 1.85 million acres have been treated as of Tuesday, according to the department.

Officials hope the spraying can avoid outbreaks of mosquito-borne diseases. Texas reported 441 human cases of West Nile virus and 21 deaths since the start of 2016, according to figures released on Tuesday. It reported 342 cases of Zika virus during the same period, including one likely spread by a mosquito bite this year.

Most mosquitoes that appear after floods are not the disease-carrying varieties but can hurt recovery operations by swarming residents and disaster workers during cleanup efforts, said DSHS spokesman Chris Van Deusen.

Harris County, the state's most populous county and home to Houston, is expected to begin night-time spraying soon, said Dr. Mustapha Debboun, director of the Mosquito and Vector Control division of Harris County Public Health.

"Under the circumstances, when you have a hurricane of a magnitude like this, we would like them to spray the whole county ... everyone was affected," Debboun said.

Harris County identified areas with dense mosquito groupings and dispatched fogging trucks every night since Sept. 4. Typically, trucks are sent only to areas with disease-carrying mosquito populations, he said.

An Aedes Aegypti mosquito is seen in a lab of the International Training and Medical Research Training Center. Reuters/Jaime Saldarriaga/

Harvey plowed into Houston last month, killing at least 70 people and causing about $180 billion in damages, largely through flooding. Trillions of gallons of water fell on the region and led to a surge in mosquitoes, prompting officials to seek U.S. Air Force help.

The C-130 cargo planes operating from an air force base in San Antonio joined two smaller aircraft that sprayed in south Texas last week. The big planes also were used to help control mosquitoes after Hurricanes Katrina, Rita and Gustav.

In Jefferson County on the eastern Texas coast, aerial spraying began Sunday and could end Tuesday, the county's mosquito control division director told Reuters. Residents were alerted to the flights and beekeepers were asked to cover hives, he said.

State officials urged residents to dispose of standing water, use repellant and wear long-sleeved clothing outdoors.