What is the risk of West Nile virus in Utah?


With COVID-19 seemingly finally on the way out, Utahns could breathe a sigh of relief for a freer summer season, but health officials warn vigilance is still needed for another virus: West Nile.

Experts are concerned as more than double the predicted number of mosquitoes hatched north of Salt Lake City in May. A recent survey by the Salt Lake City Mosquito Control District measured 960 mosquitoes in the rural area – a sharp departure from the expected 400 from the average for the past five years.

Mosquitoes are sorted by type at the Salt Lake City Mosquito District Laboratory in Salt Lake City on Thursday, May 27, 2021.
Laura Seitz, Deseret News

This large increase is probably due to the snowmelt of the mountains around the Salt Lake valley which flows into more marshy areas at their base. The water stays there, locked in and stagnant, and becomes an ideal breeding ground for mosquitoes as temperatures warm.

The Industrial Watch Zone, located between Salt Lake City International Airport and State Highway 201, also saw a 75% increase in mosquitoes over average. Any of these mosquitoes could carry West Nile virus, and the only way the Department of Health will know is to monitor and test the population.

Unlike last year, when COVID-19 complicated the mosquito testing process for West Nile, testing is expected to continue as usual throughout the summer as more clutches hatch. and more and more employees of the department are being vaccinated.

As of Thursday’s West Nile testing update, no cases have been reported in mosquito pools or in humans.

“We don’t want people to stress out and stay indoors all summer,” said Hannah Rettler, zoologist and vector-borne epidemiologist with the Utah Department of Health. “We just want people to be aware of the mosquito areas. It’s about knowing what your risk is and how to protect yourself. Then there is no need to sit down and actively worry. “

This year compared to the last

Although West Nile only infected two Utahns in 2020, Ary Faraji, executive director of the Salt Lake City Mosquito Control District, said that due to the nature of both West Nile virus and mosquitoes that carry it, a year of few cases means little for next year.

“A lot of these viruses are cyclical in nature,” Faraji said. “Some years can have a lot of positive cases, and some years, through natural ecological cycles or interventions, we see reduced activity. But these pathogens never go away. “

In fact, the cyclical trend of the disease is one of the main reasons it seems to be “forgotten” this summer. Residents may remember a string of good years, take a walk in nature as the temperature rises, and keep mosquitoes in their minds until they are confronted with one, Faraji said. By then, it’s too late to go back and grab a repellant, and one bite may be enough for a potentially dangerous infection.

West Nile virus is transmitted by the bite of an infected mosquito, but the disease itself is unable to infect most humans today. It should be kept between bird biting mosquitoes and birds; an infected mosquito bites a bird, which amplifies the disease, then another uninfected mosquito contracts the amplified disease from that same bird, amplifying it in turn. This positive feedback loop means it will be a few months before the virus grows in mosquito pools. According to Faraji, we likely won’t see infected swimming pools until the end of June.

That’s not to say the virus can’t circulate before, however, especially in high-risk groups. The goal of testing in the first months of May is to see the rate of transmission of infection in the field, or how quickly the disease is spreading among mosquitoes. If they reach a threshold of mosquito-infected pools, reduction districts will need to intensify their control efforts to stop transmission. These efforts may include setting up traps, managing water drainage systems to remove standing water, and physical screens on rain barrels to control the amount of pregnant larvae and pupae.

What is the harm?

Unlike the new coronavirus, there is no vaccine to prevent West Nile virus, nor drugs designed to identify the disease itself. Some symptoms of infection, such as fever or headache, can be treated with bed rest, fluid intake, and over-the-counter pain relievers.

However, about 1 in 150 people who are infected develop severe symptoms, which can include muscle weakness, seizures, vision loss, numbness, and death. People over 50 are at greater risk, as are those with certain medical conditions or who have received organ transplants.

“We may experience reduced transmission or reduced cases,” Faraji said. “But because of the fact that it still exists, we need to be vigilant, have an established monitoring program, and educate the public on what they can do to reduce personal risk.”

Tips for avoiding mosquito bites and potential exposure to West Nile virus:

  • Avoid areas where mosquitoes are highly visible. If you are planning a dawn or dusk outing, check the Mosquito Watch Map and see if your location is in danger.
  • Wear long-sleeved shirts and pants, and apply a Center for Disease Control and Prevention-approved repellant to exposed areas of skin, especially at dusk and dawn, when mosquitoes are more likely to bite.
  • Run a pump on your private pool or pond. If you don’t have a pump, call your local mosquito control district, who can provide you with pumps and mosquito-eating fish to naturally reduce the population.
  • If you take a bird bath, drain its water at least every five days.
  • Repair your screen door if you see a tear or puncture.
  • Put containers that collect water through rain or a sprinkler system indoors, especially during peak mosquito hours.
  • Report bodies of standing water in your neighborhood to a local mosquito control district.

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