West Nile virus
A mosquito standing on a human arm

West Nile virus in Utah

West Nile virus (WNV) is an arbovirus, or arthropod-borne virus, of the flavivirus family. West Nile virus is one of many mosquito-borne viral infections. Several similar types of mosquito-borne viral infections that cause encephalitis, such as St. Louis and Western Equine Encephalitis, have been present in the United States for some time.

In most cases, WNV produces few or no symptoms. However, in some cases, West Nile viral infection may cause more severe symptoms including encephalitis, or swelling of the brain, which can be fatal. Persons over the age of 50 may be at an increased risk of more severe forms of West Nile virus infection.

How is the virus transmitted?

A mosquito standing on a human arm
A mosquito standing on a human arm

West Nile Virus is primarily transmitted by mosquitoes of the Culex family during normal bloodfeeding. Some species in this family are ornithophilic, i.e. feed primarily on birds, and birds act as reservoirs or amplifying hosts of West Nile virus. Though many species of birds are known to contract WNV, species in the Corvid family (crows, ravens, and jays) are more susceptible to the disease and are therefore useful geographic detectors of West Nile virus.

Mammals, including humans and horses, are considered incidental hosts and are therefore viral 'dead ends.' Humans are most likely to acquire WNV from an infected mosquito, and the virus cannot be transmitted through person-to-person contact. Other mammals, such as horses, do not maintain a high enough level of the virus in the blood stream to transmit the virus to humans.

How can I protect myself and my family from WNV infection?

Prevention is still the best method of avoiding West Nile virus infection. West Nile virus is primarily spread by the bite of an infected mosquito. Protect yourself and your family against mosquito bites. It is important to follow these recommended guidelines:

  • Use mosquito repellents with DEET (30 or 35 percent concentration for adults and less than 10 percent for children) or Picaridin, especially from dusk to dawn. Mosquitoes that carry West Nile virus are most active during this time.
  • Make sure window screens and screened door are in good repair. Small holes will allow mosquitoes to enter.
  • Change water regularly (every two or three days) in birdbaths, outdoor pet dishes, etc.
  • Aerate ornamental ponds or contact your local mosquito abatement district regarding treatment options.
  • Use mosquito repellent according to label instructions.
  • Make sure window screens and screened doors are in good repair. Small holes will allow mosquitoes to enter.
  • Eliminate standing water around your home in locations such as old tires, cans, poorly kept swimming pools, or any other source where stagnant water accumulates.

For more information on protecting yourself and reducing mosquitoes around your home, visit epi.utah.gov/west-nile-virus/.

What is the role of the Division of Wildlife Resources?

In the past, the DWR assisted the Utah Department of Health with collecting dead birds as part of a national West Nile virus early detection program. Now that the virus is well-established in the United States, detection is no longer needed as a surveillance tool.

What do I do if I find a dead bird?

Finding one dead bird is not a cause for concern, and a cluster of sick or dead birds is not an indication of WNV infection. It might, however, indicate the presence of other wildlife diseases of concern. Since West Nile virus is now established in the United States, the DWR no longer collects dead birds for WNV testing.

If you notice several dead birds in a small area, these birds might have picked up parasites or bacteria from a local bird feeder. If you have a bird feeder, please clean your feeder once a month using a 10 percent bleach solution for at least ten minutes, and rinse thoroughly. If large numbers of dead birds suddenly appear in a small area, these birds might have been poisoned. Please contact your regional DWR office to report this.

If you find a dead bird in your yard use standard levels of precaution when handling it. Do not pick up a dead bird with your bare hands. Birds die from a variety of causes, and it is important to be cautious. If possible, wear rubber or latex gloves. If gloves are not available, invert a plastic bag over your hand, pick up the bird and un-invert the bag. Seal the bag with the bird inside, then place inside a second plastic bag. Seal the second plastic bag. If available, Ziploc-type bags work well.

Additional information

Follow-up studies

Local links

National links

Answers to frequently asked questions

  • Question: Is West Nile virus in Utah?
  • Answer: Yes, West Nile virus has been found in several Utah counties. Learn more about West Nile virus.
  • Question: Is there a vaccine available for humans?
  • Answer: No, there is currently no vaccine approved for use in humans. The best method of protection is to avoid contact with infected mosquitoes.
  • Question: How can I protect my horses from West Nile virus infection?
  • Answer: There is a vaccine available for use in horses. Please contact your local veterinarian.
  • Question: What are the symptoms of West Nile virus?
  • Answer: In humans, West Nile virus infection typically produces few to no symptoms. In many cases, people infected with WNV have reported feeling flu-like symptoms (i.e. headache, muscle aches and neck stiffness). In rare cases, WNV infection may cause more severe symptoms, such as encephalitis (or swelling of the brain). People over the age of 50 may be at an increased risk of more severe forms of WNV infection. For more information on the symptoms of West Nile virus infection visit the Utah Department of Health & Human Services.
  • Question: Are my pets at risk of contracting WNV?
  • Answer: Very few domesticated cats or dogs have been reported as being positive for WNV. Domestic cats and dogs are considered to be at very low risk of infection.
  • Question: Should hunters be concerned about eating the game birds they catch?
  • Answer: Some gamebirds have tested positive for WNV. However, there is no evidence of human infection by consumption of properly cooked infected game. Hunters are likely at higher risk of infection by mosquito exposure, particularly in wetland environments. Protective measures should be taken to prevent mosquito exposure while hunting. Also, WNV transmission to humans has been documented to occur by accidental injury in the laboratory and by blood transfusion. It is recommended that hunters wear gloves when dressing (cleaning) the birds to protect against accidental injury and exposure to blood. Immediately consult with a physician should an injury occur to discuss the risk of WNV exposure from the injury. Other protective measures recommended to hunters are those that prevent exposure to any infectious organisms carried by game species, including washing hands with soap and water after handling carcasses and cooking the meat thoroughly.
  • Question: I have a bird feeder and/or a birdbath on my property. Am I at increased risk of catching WNV?
  • Answer: At this time, there isn't evidence to indicate that humans can get infected directly from an infected bird. However, we recommended to always follow general hygienic procedures. Birdbaths and feeders should be washed or disinfected regularly (how to clean a bird feeder). Wash your hands with soap and water after touching the baths/feeders. To prevent mosquitoes from breeding on your property, empty and clean birdbaths at least once a week and eliminate any other standing water in your area. Contact local health officials if you are concerned about potential mosquito breeding sites in your area.