State health officials Friday added two more "probable" cases of West Nile virus in humans, bringing the probable-case count to four, to go along with Churchill County's 10 confirmed cases.
Last week, a typographical error led the Nevada State Health Division to say there were nine human West Nile cases, rather than 10, in Churchill.
Statewide, the total number of confirmed human West Nile cases is 28 so far. Thirteen are in Clark County, 10 are in Churchill, and two are in Washoe. Lyon, Douglas and Carson City counties each have one confirmed case of the virus.
Churchill County Mosquito and Weed Abatement District Manager Nancy Upham said last month that spraying for adult mosquitoes will continue in the Lahontan Valley until the first decent freeze finishes off the remaining insects, probably around the end of this month.
Next year, the district plans to use infection rate information it compiles this year to attack areas containing mosquitoes with the highest chance of carrying the disease.
West Nile virus was first discovered in the United States in 1999 in New York and New Jersey. It quickly spread across the country, but didn't show up in Nevada until this summer, when it was found in a dead crow in Carson City. At the time, Nevada was one of only three states in the continental United States not to have detected West Nile.
Since then, only Clark County, with a population more than 50 times greater than Churchill, has logged more human cases of the virus than the Lahontan Valley.
The mosquito-borne virus, while potentially hazardous, is a relatively rare medical problem for humans, health officials say.
The vast majority of people infected with West Nile don't show any serious symptoms so the infections are rarely detected. Only about 1 percent of infected humans develop the more severe encephalitis or meningitis, mainly the elderly or people with compromised immune systems.
While the chances of a person becoming seriously ill from West Nile are slim, horses are not so lucky. An estimated 30 percent of horses that display West Nile symptoms die.