West Nile virus is spreading so quickly in Dallas County that officials declared a state of emergency on Thursday.

The number of human cases of the virus in Dallas County is up to 175, and there have been nine deaths.

"This declaration will expand our avenues for assistance in our ongoing battle with West Nile virus. We are in constant communication with our state and regional partners," County Judge Clay Jenkins said in a statement.

NBC 5 has learned there is a meeting Friday at which the county will reconsider aerial spraying for mosquitoes to attack the West Nile virus.

County commissioners said no to the plan earlier this week in favor of continuing targeted ground spraying.

Dr. Edward Goodman, an epidemiologist at Texas Health Dallas and a member of the Dallas County Medical Society, which recommends aerial spraying, said ground spraying would not be enough to save lives.

Goodman said this week's rain would only make the West Nile virus epidemic worse because it leaves behind standing water where infected mosquitoes can breed.

He said he hopes to convince the county to change course.

"I'm concerned that they don't really understand that ground spraying is inherently inefficient," Goodman said. "There is a limited number of trucks, they have a limited amount of space they can cover, and they just can't cover the area comprehensively, whereas aerial spraying can take all of those issues and make them a non-issue."

West Nile virus is not expected to peak until late August. There are no approved treatments at this time, which is why doctors say prevention is so important.

Get tips on symptoms of West Nile virus and West Nile virus prevention here.

West Nile Virus Facts

Most people bitten by a West Nile virus-infected mosquito will not show any symptoms. Symptoms, if they appear, are fever, headache, nausea, body aches, swollen lymph nodes and skin rashes.

Fewer than 1 percent of those infected with West Nile virus experience the serious form of the illness. Serious symptoms include high fever, severe headache, neck stiffness, disorientation, tremors or convulsions, vision loss, muscle weakness and numbness or paralysis.

Both Dallas and Richardson are urging residents to: