On Sunday, July 14, Vector Disease Control International (VDCI) used a small airplane for aerial application of larvicide over approximately 300 acres within the Scott M. Matheson Wetlands Preserve to reduce the mosquito population. [Photo courtesy of Danielle Skidmore]

West Nile virus has been detected in mosquitoes collected from traps by the Moab Mosquito Abatement District. The Utah Department of Health reported on Saturday, July 13, that there had been three positive tests in Grand County.

The first positive test result came in on July 11 and is reported to be the first positive test in the state this year.

The virus infected 11 people in Utah last year, with one fatality, according to the Utah Department of Health. As of July 13, no persons have been reported as positive for West Nile virus.

The Utah Department of Health says West Nile virus is transmitted to people by mosquitoes, with 70-80% of people who become infected not showing any signs of symptoms. Less than 1% of those infected will develop a serious and potentially life-threatening neurological illness, such as meningitis. Others may experience headache, body aches, joint pains, vomiting, diarrhea or rash.

Lupe Simpson lives on the west side of Moab in the vicinity of where the mosquitoes with West Nile were detected. She has seen West Nile hit a family member before, and she is worried it could happen to her or another loved one.

“We are all worried,” Simpson said. “My husband, my daughter and myself have compromised immune systems. We have purchased non-DEET mosquito spray and keep doors and windows closed and stay mainly inside.”

West Nile virus can infect domesticated animals like cats and domestic rabbits, and is particularly dangerous for horses.

About one-third of horses with clinical signs of West Nile virus die from the disease, while many others still display behavior and gait abnormalities six months after diagnosis, according to the American Association of Equine Practitioners. While no vaccine to prevent West Nile virus exists yet for humans, there is one for horses.

“It’s a very, very serious disease that is preventable with a single vaccination,” said Dr. Alyssa Mulligan at Moab Veterinary Clinic. She said the vaccine costs $66 and is a combination vaccine that protects against five other serious diseases in addition to West Nile virus, including tetanus.

To combat the mosquitoes, fogging with Biomist 4+4 will continue regularly, from 9 p.m. until midnight, until further notice. Inclement conditions, including high winds, may delay spraying. Nance wrote in an email on Tuesday, July 17, that there would not be fogging on Monday, July 22, as it will be “trap night.”

Biomist 4+4 is a synthetic mixture targeting adult mosquitoes. While it is approved by regulators for residential use, its label says it is “highly toxic” to bees and “extremely toxic” to aquatic organisms, such as frogs and fish.

Simpson said she understands the need to fog for mosquitoes, although she wishes it would not hurt the bees.

Moab Mosquito Abatement District Manager Libby Nance said she is working with local beekeepers and taking other steps to minimize harm to animals other than mosquitoes.

Grand County Clerk and Auditor Chris Baird, who has been coordinating with the abatement district to facilitate the purchases of goods and services needed to combat mosquitoes, said there is a statistic that is used to determine the severity of West Nile virus outbreaks called the Minimum Field Infection Rate (MFIR).

Baird said the two most recent tests show the MFIR for the traps gathered on July 2 and July 9 at 1.24 and 1.58 MFIR respectively. The positive results for West Nile virus were both from the same trap located on Westwood Avenue.

“The information I have is that a MFIR for West Nile virus below 4 is common and not particularly alarming, although any positive test result indicates that preventative measures should be taken seriously,” Baird wrote in a statement on social media.

Nance updated the abatement district’s voicemail message on Friday, July 12, with information on the West Nile virus detection, plans to combat it and recommendations for the public to take preventative measures.

“West Nile virus is transmitted by Culex mosquitoes that bite at night, not the nuisance mosquitoes that bite during the day,” Nance said. “The peak flight time for these vector mosquitoes is in the two hours after the first stars appear after sunset.”

Nance recommended avoiding Culex mosquito bites after dark by wearing long-sleeved shirts, pants and using an Environmental Protection Agency (EPA)-registered insect repellent.

“When used as directed, these are proven safe and effective even for pregnant and breastfeeding women.” Nance said.

She added that it is “especially important” to prevent mosquitoes from entering homes at night by making sure window screens are in good condition. She said those sleeping outdoors should use a screened tent.

A July 11 press release also encouraged removing stagnant water, such as water in swimming pools, hot tubs and wading pools that are not being maintained. Removing excess water around irrigation fields and livestock troughs can help to reduce mosquito populations. Treating standing water with neem oil (sold at most garden supply stores) kills mosquito larvae in the water, according to research studies published by the National Center for Biotechnology Information at the U.S. National Library of Medicine.

In addition to the fogging, which Nance said last week reduced the mosquito population considerably, an aerial drop of larvicide occurred the morning of Sunday, July 14.

Ogden-based Vector Disease Control International (VDCI), a mosquito control company, used a single-engine airplane flying at a low altitude of approximately 300 feet to conduct an aerial application of a granular larvicide, Altosid P35, over about 300 acres within the Scott M. Matheson Wetlands Preserve. The preserve was closed for the remainder of the day.

Unlike Biomist 4+4, Nance said the larvicide has no effect on nontarget species such as bees, frogs, fish or aquatic invertebrates. The chemical’s safety data sheet says the larvicide is not classified as a carcinogen or toxin.

The total cost of the aerial application is approximately $72,250, Baird said. The county spent another $8,500 to buy equipment for fogging. The funds for the fogger, as well as the larvicide and its application, were not in the county’s original budget but were made as emergency purchases “for the purposes of community health, safety and welfare,” Baird said.

Baird said the county and abatement district will continue to coordinate mosquito mitigation efforts and the costs. He hopes the abatement district will reimburse the county over time.

The abatement district asked in their July 11 press release that “oddly sick behavior” by local birds be reported to the district, including crows, ravens, magpies, jays, hawks, eagles and owls that are susceptible to West Nile virus.

“If you see one of these birds behaving in an oddly sick manner, or find one fresh-dead for no apparent reason, contact mosquito abatement. The birds will not be collected, but their incidence can help determine the extent of West Nile virus activity,” the district said in a statement.

The abatement district’s phone number is 435-259-7161.

Larvicide and fogging combat mosquito population