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Eye On Boise

Wed., Sept. 13, 2017, 11:03 a.m.

West Nile infections in Idaho on the rise, now 4 confirmed human cases in Ada County, 10 statewide

Use of mosquito repellent is among the measures advised to avoid mosquito bites that could carry West Nile Virus. The Idaho Department of Health & Welfare advises the use of EPA-approved repellents containing DEET, Picaridin or Oil of Lemon Eucalyptus.
Use of mosquito repellent is among the measures advised to avoid mosquito bites that could carry West Nile Virus. The Idaho Department of Health & Welfare advises the use of EPA-approved repellents containing DEET, Picaridin or Oil of Lemon Eucalyptus.

Ada County is now up to four confirmed human cases of West Nile Virus, and there are 10 statewide; health officials are warning Idahoans that the danger from the mosquito-borne virus is not over, and precautions should be taken to avoid mosquito bites. You can read my full story here at spokesman.com.

Late summer and early fall is when most human cases of West Nile are reported in Idaho. “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 & 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.”

Of the four confirmed Ada County cases, two are of the most severe neuro-invasive type, which can infect the brain or spinal cord and lead to very serious illness or death; statewide, five of the 10 confirmed cases are neuro-invasive. 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.

Mosquitoes began testing positive for West Nile in Ada County in July; more and more have been found since, across the county. The county’s “Mosquito Tracker” map shows the sites here.

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. Health & Welfare has statewide data posted here.

The 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, including 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’s office of Weed, Pest and Mosquito Abatement operates numerous mosquito traps throughout the county, and when mosquitoes in them test positive for West Nile Virus, the agency conducts aerial spraying in a 1-mile square area around the trap location to reduce mosquito populations. 

“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.




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Betsy Z. Russell
Betsy Z. Russell joined The Spokesman-Review in 1991. She currently is a reporter in the Boise Bureau covering Idaho state government and politics, and other news from Idaho's state capital.

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