Cities across the nation are taking precaution as this summer's hot weather spawns more deadly cases of West Nile virus.

At least 42 states have reported cases, with Texas being the hardest hit.

In Dallas County, officials declared a public health emergency following 175 infections. Nine people there have died after getting the virus.

Mosquitos are now so bad in Dallas County, five planes have been requested for spraying pesticides in heavily populated areas.

"We are talking about a third-world virus. We don't have a blueprint that says this works, you know, versus another plan," said Zachary Thompson, director of Dallas County's Health and Human Services.

"This is a matter of extreme concern, and we're going to follow the science and do what's best for our people," added Dallas County Judge Clay Jenkins, the county's top elected official.

Scientists say warmer weather came earlier than usual, shortening the cold weather freezes that usually kill off mosquitoes carrying West Nile.