Scott Arbon at Deer Flat Wildlife Refuge (copy)

Canyon County Mosquito Abatement larvicide technician Scott Arbon inspects marsh water at Deer Flat Wildlife Refuge, in this 2017 file photo.

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A Canyon County resident over age 50 has been confirmed as suffering from the dangerous, neuroinvasive form of West Nile Virus, and officials are warning Treasure Valley residents to drain standing water left from recent rains to avoid breeding mosquitoes that can carry the virus.

The Canyon County case was the third human West Nile Virus case reported in Idaho so far this year; the first two were in Ada County residents, though they didn’t suffer the most serious form of the disease.

“It’s a great reminder to keep wearing the insect repellent and long sleeves and long pants, if you’re going to be out when mosquitoes are out,” said Niki Forbing-Orr, spokeswoman for the Idaho Department of Health & Welfare.

West Nile Virus is spread through the bite of an infected mosquito, and not from person to person. It first showed up in Idaho in 2003; in 2006, Idaho led the nation with nearly 1,000 cases and 23 deaths.

This week, mosquito abatement districts in Ada, Canyon, Gem and Payette counties launched a “Drain the Rain” campaign, warning that after recent monsoonal rainfall, water has inundated many areas of southwestern Idaho. Mosquitoes can develop in as little water as the volume in a bottle cap, the four districts warned in a joint news release.

“Old tires, plant water catch trays, child toys, wheelbarrows, buckets, clogged rain gutters, uncovered boats, and other water-holding items are all capable of producing the types of mosquitoes that transmit West Nile virus,” the districts warned, and that water should be drained.

“Now is the time to work together to eliminate potential mosquito development sites and lessen the impact mosquitoes have in our neighborhoods,” said Jim Lunders, director of the Canyon County Mosquito Abatement District.

Ricky Bowman, program manager for Southwest District Health, said while eight in 10 West Nile infections result in mild or no symptoms, “About one in 150 people infected with WNV develop severe illness such as encephalitis (inflammation of the brain) or meningitis (inflammation of the linings of the brain and spinal cord). These more severe infections are marked by a rapid onset of a high fever, headache, neck stiffness, body aches, disorientation, and tremors, and may require hospitalization.”

In 2020, Idaho saw six human West Nile Virus infections and no deaths, but five of the six were of the dangerous neuroinvasive type. That included three residents of Ada County; one in Gem County; and one in Gooding County.

In 2019, Idaho reported 13 symptomatic human cases of West Nile Virus, including five patients who suffered from the neuroinvasive disease.

In 2018, Idaho had 16 cases, and 10 were neuroinvasive disease, according to the Idaho Department of Health & Welfare.

From 2003 to 2019, Idaho had 1,382 human infections, of which nearly 20% were classified as neuroinvasive. A total of 30 Idahoans died from West Nile over that time.

In addition to people, horses and birds can be infected with West Nile Virus. There’s a vaccine for horses; there isn’t one for humans.

Forbing-Orr said thus far this year, Idaho’s reported no positive infections among horses or birds, though mosquito populations in at least half a dozen counties, including Ada and Canyon, have tested positive for the virus.

The number of human West Nile infections in Idaho has varied in the past decade, from just three in 2011 to 40 in 2013 to 13 in 2019.

Betsy Z. Russell is the Boise bureau chief and state capitol reporter for the Idaho Press and Adams Publishing Group. Follow her on Twitter at @BetsyZRussell.

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