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The original item was published from 9/12/2016 12:30:00 PM to 1/1/2017 12:05:04 AM.

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Posted on: September 12, 2016



Moab Mosquito Abatement District
1000 E. Sand Flats Road
P. O. Box 142
Moab, UT 84532
Robert A. Phillips, Director/ Entomologist Phone 435-259-7161


September 8, 2016
Contact: Bob Phillips, 259-7161


West Nile virus was found in mosquitoes collected September 7 by the Moab Mosquito Abatement District in the Matheson Preserve northwest of Moab. This is the first detection of the virus in the Moab area this season and comes two months later than in some other years.
West Nile virus is transmitted by Culex mosquitoes that bite at night anywhere in the valley or during mild periods of the day in the bulrush marshes of the Preserve. The peak flight time for the vector Culex mosquitoes is in the two hours after the first stars become visible at sunset. If insecticide spraying (fogging) is needed, it will be done at that time and in those areas where Culex numbers pose significant risk. Currently, Culex numbers outside the marsh are very low and below the District’s spray threshold, but surveillance will continue to see if there are any changes.
People should avoid mosquito bites by using long sleeves and repellent. It is especially important to prevent night mosquito bites by having good window screens and by using a screened tent if sleeping outside. Though the risk is low, people should take measures to avoid nighttime mosquito bites.
West Nile virus activity will continue in birds and mosquitoes for about two weeks and then be restricted to the Preserve and decline as temperatures cool down. Our primary vector mosquito, Culex tarsalis, stops biting around the fall equinox (September 22 this year) as it prepares to go into its winter diapause. Our secondary vector mosquito, Culex erythrothorax, continues biting until frosts kill it off but stays in and near the bulrush marshes northwest of town.
Because of declining mosquito numbers and the imminent arrival of fall, spraying of adult mosquitoes is not likely. However, if spraying is needed, it will be based on local Culex mosquito trap counts and infection rates.
The insecticide spray the Mosquito District uses for adult mosquitoes is a pyrethrum and piperonyl butoxide mixture. It is relatively odorless, does not harm paint, is legal for use on crops and pastures, and breaks-down within a few hours after application. However, it can cause allergic responses, including severe asthma attacks, in susceptible individuals.
If spraying needs to be done, announcements will be given to KZMU and KCYN, and an attempt will be made to notify those in the spray area who are on the District’s “chemically sensitive” list so that individuals may take personal precautions. Those who want to be on the list should call Mosquito Abatement at 259-7161 and leave their name, address, and phone number or email address. The information will be kept confidential and be used only for spray notification. Because it has been several years since the last list was compiled, those who called before should call again to be placed on a new list.
The District does not intend to skip property within a spray area. The spray is supposed to drift, and therefore it would be ineffective and misleading to turn it off for one property and then turn it back on for their neighbors. Those who are chemically sensitive should go somewhere else for the evening or take other measures to avoid exposure. The District will spray only if the disease risk is determined to be significant.
Even if a person is infected by West Nile virus, the risk of serious disease is low. Four-fifths of those infected will not get sick. Most of the remainder will have a mild to severe flu-like illness with muscle aches, fever, rash, and headache that usually lasts a few days but can last months. Less than one in a hundred will get meningitis or encephalitis. Those at greatest risk of serious disease are those with weakened immune systems, diabetes, high blood pressure, or kidney disease. The elderly are at greatest risk for severe complications. The overall death rate is about one for every thousand infected, and the average age of those who die from the disease is about 70. People with normal immune systems are thought to acquire life-long immunity after infection.
Proper diagnosis of West Nile virus disease is important. The incubation period is usually one to two weeks, and many other viruses – from herpes to influenza – can cause similar symptoms including encephalitis.
Horses are much more likely to suffer from the virus. About one in ten will become ill, and half of those will die or have to be euthanized. However, no properly vaccinated horse is known to have suffered significant illness from the virus. With only about a month of vector mosquito season left, it is likely too late to properly vaccinate horses for this year. Contact your veterinarian about this, and, at least, be prepared to vaccinate your horses early next year. Annual boosters are required.
Crows, ravens, magpies, jays, hawks, eagles, and owls are often killed by West Nile virus. However, due to budget cuts, the state is no longer testing these birds. 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 at 259-7161. The birds will not be collected, but their incidence can help determine the extent of West Nile virus activity in the area.
Culex mosquitoes breed in water that stands for more than a week. Unmaintained swimming pools, hot tubs, wading pools, water filled buckets, livestock water troughs, and flood-irrigated fields breed these mosquitoes. If people remove stagnant water from their property and irrigators properly manage their water, fewer Culex will be produced. To report stagnant water, call Mosquito Abatement at 259-7161.

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