The Iowa Department of Public Health says there have already been three reported cases of West Nile virus in the state, even though the disease usually is seen in early autumn.
The agency says cases have been reported in Clay, Monona and Woodbury counties. Mosquitoes carrying the virus also have been detected in central Iowa.
Officials say the best way to avoid the disease is to avoid outdoor activities at dusk and dawn when mosquitoes are most active, use insect repellent and wear long-sleeve shirts and pants. They also encourage people to eliminate standing water, where mosquitoes lay eggs.
About 20 percent of infected people suffer mild to moderate symptoms, including fever, headache and vomiting.
Less than 1 percent become seriously ill, and people can die of the disease.