West Nile virus is moving westward rapidly, but it's not a threat for Nevadans yet, according to Doris Dimmitt, infection control coordinator at Carson-Tahoe Hospital.
"I've received several calls from community members concerned about contracting West Nile from local mosquitoes," she said this week. "The virus is not expected to reach Nevada mosquitoes this year, per the Centers for Disease Control. Beyond that, they are hesitant to predict."
The disease, which started in New England in 1999, has been found as far west as Colorado and Wyoming.
"We may see a case of West Nile here, but it would be someone infected elsewhere," Dimmitt said. "The disease is not contagious. It is passed through infected mosquitoes and is not transmitted person to person."
According to the national Centers for Disease Control, human illness from West Nile virus is rare, even in areas where the virus has been reported and the chance anyone is going to become ill from a mosquito bite is low. Most people infected with the virus will have either no symptoms, or mild ones.
Thirty-seven states have reported West Nile activity this year and 251 human cases have been reported, 147 of those in Louisiana. Nationwide, 15 of those cases were fatal, the deaths were caused by a severe complication known as West Nile encephalitis, an inflammation of the brain. The risk is highest for persons 50 and older, disease control center officials in Atlanta said.
The virus is transmitted primarily between mosquitoes and bird hosts. Birds sustain the virus in the bloodstream for one to four days. During that period, the virus can be reintroduced to mosquitoes, but after that the birds normally acquire a life-long immunity, the disease control center said.
Some birds infected with the virus do become ill. The disease has been confirmed in 3,128 dead birds representing 110 species. Crows and jays are most often infected.
The virus does not usually reproduce adequately in mammals and consequently is not transmitted through them.
West Nile virus apparently doesn't cause extensive illness in dogs or cats. A test that indicates exposure to the virus in New York revealed dogs in the 1999 epidemic area were frequently infected, but none actually acquired the disease, the disease control center said.
Horses are hardest hit by the infection, with a 40 percent mortality rate. A West Nile virus vaccine recently was licensed for horses, but its effectiveness is unknown.
According to disease control center officials, there is no reason to destroy an infected horse or any other animal. The majority recover completely from the infection.
Nevadans traveling to infected states can reduce their risk by using insect repellent containing DEET. When possible, wear long-sleeved clothes and stay indoors during peak mosquito times, like dawn and dusk, experts advise.