Dr. Richard Besser on 'Good Morning America': Worst year ever for West Nile virus

CLEVELAND - West Nile virus has taken its toll on people in 43 states, the Centers for Disease Control says, in what is a widespread national outbreak.

On "Good Morning America" Thursday, ABC News Chief Health and Medical Editor Dr. Richard Besser, who spent years studying deadly diseases with the CDC, called 2012 "the worst year ever for West Nile virus."

The CDC reports 693 cases and 26 deaths resulting from West Nile thus far this year.

Besser said as many as 12,000 people have been sickened by the disease.

He said they believe the reason for the outbreak is related to this past winter's mild weather.

"You count on that cold to kill mosquitoes and that didn't happen, so mosquitoes this year are really abundant," Besser said.

The widest group affected are 50-year-olds and up who are active and outside. 80 percent of people infected by the disease don't experience symptoms, while the other 20 percent feel flu-like symptoms.

So how can you keep you and your family safe?

Besser advises that dusk and dawn are the worse times, to use repellent, cover exposed skin and remove standing water.

A 54-year-old Shaker Heights resident became a reported case of the West Nile virus on Tuesday. A Cleveland man was hospitalized with West Nile virus in early August. The Cleveland Department of Public Health said that was the area's first case for 2012 and happened about a month earlier than previous years.

Nine cases have been reported in the state this year.