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West Nile cases in Idaho on the rise, officials warn of continuing risk

UPDATED: Wed., Sept. 13, 2017, 4:56 p.m.

A field technician for Ada County Weed, Pest and Mosquito Abatement applies larvicide treatment to kill mosquito larvae; the agency also has been fogging areas where traps have detected West Nile Virus in adult mosquitoes to reduce the adult mosquito populations. So far this year, Ada County has four confirmed human cases of West Nile Virus; Kootenai County has one. (Ada County)
A field technician for Ada County Weed, Pest and Mosquito Abatement applies larvicide treatment to kill mosquito larvae; the agency also has been fogging areas where traps have detected West Nile Virus in adult mosquitoes to reduce the adult mosquito populations. So far this year, Ada County has four confirmed human cases of West Nile Virus; Kootenai County has one. (Ada County)

BOISE – The number of Idahoans infected with West Nile Virus has jumped in the past week, and health officials are warning that the danger’s not over – most infections are reported in late summer or early fall.

Washington has yet to report a human case this year other than one a resident who contracted the virus out-of-state, but infected mosquitoes have been found in both North Idaho and eastern Washington, and precautions are advised, from using mosquito repellent to repairing window screens.

“The mosquito that tends to carry West Nile Virus tends to hatch later in the summer,” said Niki Forbing-Orr, spokeswoman for the Idaho Department of Health and Welfare. Initially, those mosquitoes feed on birds, but later in the summer they’re more likely to feed on humans, she said. “So it’s a good idea to do everything you can to just continue to prevent mosquito bites.”

Idaho has now seen 10 confirmed human cases of the virus this year, with four of those just confirmed in the past week; five of the cases are of the most severe neuro-invasive type, which can infect the brain or spinal cord and lead to very serious illness or death.

Idaho had nine human cases of West Nile Virus last year; the prevalence varies from year to year. In 2006, Idaho led the nation for West Nile illnesses with almost 1,000 human infections that contributed to 23 deaths.

Thirteen Idaho counties have seen local mosquitoes test positive for West Nile this year. North Idaho saw its first locally acquired human case in early August when a Kootenai County resident contracted the virus from a mosquito bite.

In Washington, mosquitoes in four counties, including Spokane, Grant and Benton counties, have tested positive for the virus, according to the Washington State Department of Health. Birds have tested positive for the virus in Lincoln, Spokane and Walla Walla counties, and six horses in Spokane County have contracted the virus.

West Nile Virus is spread by bites from infected mosquitoes; it’s not passed from one human to another. In most cases, the virus causes few or no symptoms, but severe cases can lead to meningitis, encephalitis or death.

About one in five people who are infected experience symptoms, which develop three to 14 days after the mosquito bite. Symptoms may include fever, nausea, headaches, body aches, swollen lymph nodes in the neck and a skin rash on the chest, stomach and back.

Precautions include using insect repellent; wearing light-colored, long-sleeved shirts and long pants when outdoors; avoiding being outdoors at dusk and dawn when mosquitoes are most active; ensuring window and door screens are in place and in good repair; and removing standing water that can provide breeding grounds for mosquitoes.

West Nile Virus has no specific cure; severe cases are treated with intravenous fluids, help with breathing and nursing care.

Ada County has the most human infections in Idaho, with four as of Wednesday, up from two a week earlier; two of the four are of the neuro-invasive type.

The southern Idaho county, home to the state capitol and the state’s largest population center, has detected infected mosquitoes in 65 traps so far this summer; it’s conducted aerial spraying in a 1-square-mile area around each of those within 24 hours to reduce mosquito numbers. “We can’t obviously kill them all – we want to,” said Ada County spokeswoman Kate McGwire.

Six Ada County traps found infected mosquitoes in the past week.