Ten days after confirming the first human case of the West Nile virus in Nevada, Clark County officials have announced two other probable human cases.
The unrelated cases involve county residents over the age of 50. One victim is hospitalized, while the other sought medical care but has not been hospitalized, health officials said.
At the same time in northern Nevada, Lyon County has declared a state of emergency because of the spread of the West Nile virus in parts of the county.
Twenty-one birds, five horses and 18 mosquitoes had tested positive for the virus as of Friday in the rural county, said Nevada Agriculture Department officials.
The three Clark County human cases are among five reported in the state since July 1. The other two were in Washoe and Churchill counties.
In the Washoe County case, health officials said it will be difficult to determine where the person got the disease because of recent trips to other Western states.
Officials said the Churchill County victim is over 50 and appears to have contracted a severe form of the mosquito-borne illness while in Nevada.
Confirmation tests for the other four cases were pending.
The only confirmed human case involves a victim under the age of 50 who apparently contracted the disease near his home in the northern part of the Las Vegas valley. Tests near his home confirmed the presence of infected mosquitoes.
The victim was hospitalized in July, but has since been released and recovered from the illness.
Clark County officials are stepping up enforcement of laws designed to abate improperly maintained and abandoned swimming pools that act as potential mosquito breeding grounds.
Health officials said they have encountered difficulty in gaining the permission of some property owners to treat stagnant pool water with pellets that inhibit the growth of mosquito larvae.
Under state law, uncooperative property owners will be issued a formal notice to treat water within 24 hours.
In Lyon County, officials are asking the Nevada Emergency Management Division for $20,000 to expand mosquito spraying from Mason Valley to Smith Valley.
Officials said the West Nile virus has reached epidemic proportions in Mason Valley.
The virus is carried by birds and can be transmitted to people and animals through mosquito bites.
Officials urge people to spray themselves with mosquito repellent containing DEET when outdoors and to remove standing water from their property. They also urge the public to avoid spending time outside at dusk and dawn when mosquitoes are most active.
The disease has sickened more than 260 people across the country so far this year, according to the federal Centers for Disease Control and Prevention. There is no antidote or known vaccine.