News Flash


Posted on: October 2, 2023

West Nile Virus Found in Nevada County


A case of West Nile Virus was identified in Nevada County in September.  The patient is now home and doing well.

While many areas throughout California have already experienced West Nile Virus this year, this is the first human case of the disease in Nevada County this year.  The last diagnosed case of West Nile Virus in Nevada County was in 2018.   

The Nevada County resident who contracted West Nile Virus first developed a fever and meningitis symptoms and was evaluated in the emergency room in early August. Then, the person’s primary doctor ordered a lab test that confirmed West Nile Virus a month later. The confirmed case was finally reported to Nevada County Public Health.  The person had not travelled internationally or had any domestic travel outside of the local surrounding area.  

Local health providers have been notified about the case.

Most people with West Nile Virus do not have any symptoms, but one in five become sick with fever and may also have other symptoms such as fever, headache, body aches, joint pains, vomiting, diarrhea or rash.  About one in 150 people develop serious disease such as meningitis and encephalitis or long-term symptoms.   

Residents who develop symptoms of West Nile Virus should seek medical care as soon as possible.

West Nile Virus is transmitted to people through the bite of an infected mosquito.  The disease occurs in birds, both wild and domestic, as well as dogs and cats, but especially horses.   West Nile Virus is most often spread to people during the summer and early fall when mosquitoes that carry West Nile Virus are most active.  

“The West Nile Virus surveillance program previously documented a West Nile Virus infection in a flock of sentinel chickens in late August in Nevada County so we knew the virus was in the County, but we had not seen any human cases,” said Nevada County Health Officer Dr. Sherilynn Cooke.  “This flock is used as an early warning system to detect infectious diseases which can affect both birds and humans.”

Statewide, there have been 153 cases of West Nile Virus in humans, 21 cases in horses, and 567 cases in dead birds in 2023 to date.

The best way to prevent the virus is to protect yourself from mosquito bites and prevent mosquitos from breeding.  

 “Our Environmental Health Vector Control Team is increasing monitoring and treating standing water and ponds in Nevada County,” said Environmental Health Director Amy Irani. “Standing water is a mosquito nursery. Mosquitoes can hatch in a week or less in as little as a half-inch of water. If you get rid of still or stagnant water at least weekly, you will keep many mosquitoes from breeding and take a big step toward protecting yourself and your family.”

Residents of Nevada County should take these actions to protect all of us.  

  • Use insect repellent: DEET, picaridin, or oil of lemon eucalyptus is recommended. 
  • Protect yourself most DAWN and DUSK: mosquitoes are more likely to bite during the early morning and evening, so make sure you wear proper clothing and repellent if outside during these times.
  • Drain standing water: mosquitoes lay eggs on standing water; so it is important to eliminate or drain all standing water sources around homes and properties.

 Currently, there is no vaccine for West Nile Virus; the best method of not contracting the disease is to prevent contact with mosquitoes using the above methods. 

The public is encouraged to assist in the efforts to detect and monitor West Nile Virus by calling the WNV hotline at 1-877-968-2473 or (1-877-WNV-BIRD) if they find a crow, raven, magpie, jay, or hawk that has been dead for about a day. Birds play an important role in maintaining and spreading this virus. Mosquitoes acquire the virus from infected birds, and then transmit the virus to people. Evidence of the virus in dead birds is often the first indication that WNV has been introduced into a new region.




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