The Idaho Department of Health and Welfare has reported Blaine County's first cases of West Nile virus infection in humans.
Spokesperson Tom Shanahan said the department was informed of two cases on Aug. 14. Both cases involve fever but not the more serious neuroinvasive form of the disease.
Until this month, there had been cases of infected animals reported in Blaine County, but not humans.
Five people have died from West Nile virus in Idaho this year, all of them elderly. Three of the fatalities occurred in Elmore County, and one each in Lincoln and Minidoka counties.
A sixth case, that of a boy near Gooding, involved simultaneous cases of West Nile virus and Rocky Mountain spotted fever, contracted from a tick bite. Monie Smith, public information officer for South Central District Health, said the boy's death was attributed primarily to the spotted fever.
Common in Europe, Asia and Africa, West Nile virus was first detected in the Americas in 1999 near New York City. It has since spread to every state in the United States except Alaska and Hawaii, and has spread rapidly through most of Idaho since the first case of human infection was reported in November 2003. In 2005, there were 13 cases statewide. So far this year, there have been 327 cases. Due to their high populations, Ada and Canyon counties have registered most of those.
The disease is transmitted through the bites of infected mosquitoes, which become infected themselves after biting infected birds. Crows and magpies appear to be the most common carriers.
According to the Idaho Department of Health and Welfare, symptoms in humans occur three to 14 days after being bitten and include fever, headache, body aches, tiredness, occasional eye pain and enlarged lymph nodes. However, only about 20 percent of West Nile infections result in illness.
"A lot of us get exposed to it and don't even know we've had it," Smith said.
Most cases of illness occur in people over 50 or those with weakened immune systems or other medical conditions. Less than 1 percent of infected people develop the more serious neuroinvasive form of the disease, whose symptoms can include high fever, stupor, coma, tremors and paralysis. Idaho has reported 39 such cases so far this year. Severe cases result in encephalitis or meningitis, which are inflammations of the brain.
A vaccine is available for horses, but not humans. There is no treatment for the virus.
As the disease has spread across the United States, typical infection patterns have been sharp spikes followed by rapid declines as people develop immunity to the virus. For example, Colorado experienced 2,947 cases of West Nile virus in 2003, but only 106 cases two years later.
"That is what we are hoping will happen here," Smith said.
However, she said, there is no reason to believe the disease will disappear.
"It is part of our ecosystem now and will stay that way," she said.
Even though most mosquitoes do not carry the virus, Smith advised people to assume that every mosquito they encounter does. She recommended that people use insect repellent when outside and wear long pants and long-sleeved shirts around dawn and dusk, when mosquitoes are most active.
The Department of Health and Welfare recommends that people get rid of all sources of standing water around their homes, including flower pots, old tires, bird baths and clogged gutters.
Most animals, including dogs and cats, do not appear to be affected by the virus. However, horses are. According to the Department of Health and Welfare, about one-third of the horses that contract the infection die. Horse owners are encouraged to contact their veterinarian about getting their animals vaccinated.