"This is earlier than we're use to seeing a first case," Heaton said.

He said about 20 percent of those who get infected from a mosquito show the flu-like symptoms of the virus and that the severe brain and spinal injuries that can cause death or disability are rare.

Older people face an increased risk of infection, as do individuals with diabetes. Heaton said last year in Utah there were 70 reported cases of humans infected with the virus, of which two people died.

Health officials urge the use of mosquito repellents containing DEET or picaridin when outdoors. They also encouraged Utahns to wear long-sleeved shirts and pants and rid their properties of standing water that gathers in old tires, buckets and wading pools.

- Mark Havnes and Erin Alberty