DRAPER — At least some mosquitoes in Draper are carrying the West Nile virus, health officers announced Wednesday.

There are no reports of anyone falling ill, according to the Salt Lake County Health Department. The virus was not detected anywhere else in the county.

But it's not just Draper residents who should be cautious, said Nicholas Rupp, the health department's communications coordinator. Others in the county should wear repellent because West Nile can spread quickly from town to town, he said.

Rupp said the virus typically is identified in mosquitoes around July Fourth.

"We don't want to cause panic, because West Nile virus is rare," Rupp said, but noting that in some cases, it can be very serious.

About 70 to 80 percent of people who contract the virus do not feel sick. Some develop a fever or other mild symptoms that do not need medical treatment.

Much less often, West Nile can cause permanent neurological effects or result in death. Most at risk are those over 60 years old and people with certain medical conditions.

Last year, one person over the age of 50 in Salt Lake County became seriously ill with West Nile. The patient survived but had neurological problems, Rupp said. The agency is not releasing other information about the case.

In the 10 years since the virus made its way to Utah, nine people have died and 349 have been infected.

In 2016, there were 13 other reports of West Nile in Utah: 11 in Salt Lake County, one in Utah County and one in Duchesne County, according to the National Centers for Disease Control. Neighboring Colorado recorded 149 cases and Nevada had 16.

Wednesday's announcement marked the first time this summer that the virus has been detected in Utah's most populous county, the department said. Mosquito abatement employees are spraying ahead of the Draper Days festival, which starts Thursday. The county says it will provide fairgoers in ticket lines with bug repellent.

Symptoms of West Nile virus appear within three days to two weeks after infection. They include fever, headache, joint pain, diarrhea and vomiting.

Mosquitoes are known to be most active after dusk and before dawn. Health officers urge anyone going outdoors during that time to:

• Use repellent

• Wear long sleeves and pants

• Clean or drain pools, ponds or other standing water in yards

• Check condition of window and door screens

• Cut grass and weeds, because mosquitoes take shade there when it's sunny.