West Nile virus detected in Ada County mosquitoes, take measures to protect yourself against bites

June 20, 2023
Dr. Leslie Tengelsen, Division of Public Health

The Ada County Weed, Pest, and Mosquito Abatement agency reported the first 2023 detection of West Nile virus (WNV) in samples of mosquitoes found in the Ada County city of Meridian on June 14 and 15. Mosquito abatement personnel were sent to the area to initiate control measures.

The risk of acquiring the WNV infection from mosquitoes will remain elevated throughout the state until a killing frost arrives in the fall, eliminating the mosquito-associated risk. It is important for people to protect themselves from mosquitoes, particularly between dusk and dawn when mosquitoes are most active. Tips to avoid mosquito bites include:

  • Cover exposed skin when outdoors and apply DEET or other EPA-approved insect repellent to exposed skin and clothing. Carefully follow instructions on the product label.
  • Insect-proof your home by repairing or replacing worn or damaged screens. 
  • Reduce standing water around homes and properties. Check and drain toys, trays, and pots that are outdoors and can hold water.
  • Change bird baths, static decorative ponds, and animal water tanks weekly to reduce suitable mosquito habitat.

During most WNV seasons, infected mosquitoes are typically detected starting in early July. However, during some years, positive mosquitoes have been detected as early as the last week of May and as late as the third week of August. Although it is hard to predict if this will be a year with lots of WNV in the community, the detection of virus this early is a warning to take precautions now and avoid mosquito bites.

West Nile virus-infected mosquitoes, people, and horses are predominantly found in communities in south and southwest Idaho. However, the virus has been detected statewide since it was first found in the state in 2003.

Every year the risk for acquiring WNV increases throughout the summer months as Culex mosquito populations thrive. Culex tarsalis and Culex pipiens are the most likely mosquito species to carry and transmit WNV in Idaho, and public health officials fully expect to find additional WNV-positive mosquitos throughout the state this summer.

WNV is spread by the bite of an infected mosquito, and not spread from person-to-person through casual contact. Symptoms can include fever, headache, body aches, nausea, and sometimes swollen lymph glands or a skin rash.

Infection can result in severe illness, especially in people 50 years of age and older. If you feel ill and think you had a mosquito bite, talk to your healthcare provider about testing for WNV.

WNV does not typically affect domestic animals, like dogs and cats, but can cause severe illness in horses and some species of birds. Although there is no vaccine for people, there are vaccines for horses, which should be given annually.

For more information about WNV, please visit http://westnile.idaho.gov.

Ada County Weed, Pest, and Mosquito Abatement https://adacounty.id.gov/weedpestmosquito/.

What about ticks and tick-borne diseases?

Spring and summer also kick off tick season in Idaho. Ticks can also transmit diseases, including Rocky Mountain Spotted Fever, tick-borne relapsing fever, and tularemia. Lyme disease is rare in Idaho and generally occurs in people who traveled to parts of the country where it’s common.

The best way to protect from tick-borne illness is similar to preventing mosquito bites: cover exposed skin when outdoors, use DEET or other EPA-approved insect repellents that include tick protection, and insect-proof your home. Also check for and remove ticks from your clothing, body, hair, and pets before coming inside. You can also talk with your veterinarian about tick prevention products for your pets. Ticks can easily hitch a ride on your pet and end up in your home.

Most tick-borne diseases found in Idaho cause a fever, and some can cause a rash. For those with Rocky Mountain Spotted Fever, symptoms can include fevers and chills, headaches, confusion, and a rash that may begin a few days after the other symptoms start.

To learn more about tularemia and tick-borne relapsing fever visit these CDC websites: https://www.cdc.gov/tularemia/index.html and https://www.cdc.gov/relapsing-fever/index.html

Leslie Tengelsen, PhD, DVM, is the state public health veterinarian in the Division of Public Health. She has worked for the department since 1998 and focuses on zoonotic disease prevention.

The Idaho Department of Health and Welfare is dedicated to strengthening the health, safety, and independence of Idahoans. Learn more at healthandwelfare.idaho.gov. 

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