General Contact Number: (530) 621-5567

Vector Control

West Nile Virus (WNV) Information

WNV Fact Sheet

WNV Activity in El Dorado County

Mosquitos in the Tahoe Area

Phone Dead Bird Hotline 877-968-BIRD

Fight the BiteHow Best to Avoid West Nile Virus....Follow the Four (4) D's:

1. Drain the water. Eliminate all sources of standing water that can support mosquito breeding.

2. Avoid going out during dusk and dawn. Mosquitoes are active during these times. They are especially active for two hours after sunset.

3. Dress appropriately. Wear long sleeves and long pants. Also make sure that doors and windows have tight fitting screens. Repair or replace screens that have tears or holes.

4. Wear a good repellant that has DEET in it. Apply according to directions. Click on the 'Edit' icon (edit icon) in the top-right corner of this widget to select Content/Form you wish to display.





West Nile Virus (WNV) Information:

The following basic information can be found in a brochure developed by the California Department of Health Services (DHS), and is available at El Dorado County Environmental Management Offices.

West Nile Virus (WNV) is a mosquito-borne virus that has been found in parts of asia, eastern Europe, Africa, and the Middle East. The virus was first detected in the United States in 1999 in New York City.

The majority of people and animals that are infected with the virus have a mild illness or no symptoms. In rare cases, the virus can cause a more serious condition called encephalitis, an inflammation of the brain. The elderly are at a higher risk for disease caused by WNV. In 2002, a total of 44 states reported WN virus activity and over 4,000 human cases were reported including over 250 deaths.

WNV is transmitted to people and animals by infected mosquitoes. Only certain species of mosquitoes carry the virus and very few mosquitoes are actually infected. A mosquito first acquires the infection by feeding on a bird with virus in its blood. The virus lives in the mosquito and is transmitted to a new host in the mosquito's saliva when the insect bites a person or animal. The virus is most prevalent from May to October when mosquitoes are most abundant . Human-to-human transmission of WNV generally does not occur. However, human WNV infection was associated with blood transfusions and organ transplants from infected donors in 2002.

Most people who are infected with WNV have no symptoms whatsoever. However, of those who become ill, symptoms can include fever, headache, nausea, body aches, mild skin rash, or swollen lymph nodes. In a few cases, the disease will progress to encephalitis (inflammation of the brain). The time between the mosquito bite and the onset of illness, known as the incubation period, ranges from 5-15 days in humans, It is estimated that 1 in 150 people who are infected with WNV will required hospitalization. Of the over 4,000 confirmed human cases of WNV in the U.S. in 2002, 6% died. The elderly are particularly susceptible to clinical illness caused by WNV. There is no specific treatment for infection with WNV, although supportive care is important.


WNV Cycle

An infected mosquito can bite any animal, but not all animals will become infected. The disease most often affects birds, but occasionally causes disease in other animals as well.

Birds - Wild birds are the animals from which the mosquito vector primarily acquires the virus. Infection has been reported in more than 100 bird species. Although many birds that are infected with WNV will not appear ill, WNV infection can cause serious illness and death in some birds. The most severe illnesses are seen among the corvid birds, which include crows, jays, ravens, and magpies. American crows constitute the majority of birds reported dead due to WNV.

Horses - Like people, most horses bitten by mosquitoes will not become sick with WNV. However, of those that do, signs may include stumbling, circling, hind leg weakness, inability to stand, muscle tremors, and death. A vaccine to prevent WNV illness in horses is available from your veterinarian. WNV vaccine and other vaccines against mosquito-borne diseases (western equine encephalitis and eastern equine encephalitis) should be given in the early spring. More information on WNV and horses.

To decrease exposure to mosquitoes and the infections they may carry:

  • Avoid spending time outside when mosquitoes are most active, especially at dawn and dusk. ◦When outdoors, wear long pants, long sleeve shirts, and other protective clothing.
  • Apply insect repellent according to label instructions.
  • Make sure that doors and windows have tight fitting screens. Repair or replace screens that have tears or holes.
  • Eliminate all sources of standing water on your property that can support mosquito breeding.
  • Contact your local mosquito and vector control agency if there is a significant mosquito problem where you live or work.
  • Mosquito Fish: Defense from Mosquitoes

The California Department of Health Services (DHS) has overseen a statewide mosquito-borne encephalitis surveillance program since 1969 for Western equine encephalitis (WEE), St. Louis encephalitis (SLE), and other viruses. In 2000, DHS and other agencies expanded the program to enhance the ability to detect WNV. A protocol to report and test dead birds was added to the existing surveillance system for encephalitis cases, mosquito testing, and monitoring of sentinel chickens.

Encephalitis Case Surveillance
DHS tracks cases of human, horse, and ratite (e.g., emu, ostrich) encephalitis. The routine testing of encephalitis cases for WNV assists in the early detection of the virus in California. Human and animal encephalitis cases are also routinely tested for WEE and SLE viruses.

Mosquito Testing
Mosquitoes throughout the state are sampled for the presence of WNV, WEE, and SLE viruses. Local mosquito and vector control agencies also monitor the abundance and type of mosquitoes.

Sentinel Chicken Testing
Over 200 chicken flocks are strategically placed throughout the state and are tested routinely during the mosquito season to detect evidence of infection from WNV, WEE or SLE viruses.

Dead Bird Surveillance
California began to test dead crows and related birds for WNV in 2000. Monitoring dead crows and other birds will help identify where the virus is occurring in the State. State agencies, private organizations, and individuals participate in the surveillance program by reporting dead bird sightings. DHS arrange to collect the dead bird from the location it was found if WNV testing is appropriate.

American Crow - American crows are found throughout most of California. They have entirely black plumage, black beak, and black feet. Adult size is 17-21 inches from tip of tail to tip of beak.

If you find a dead bird, particularly a crow, jay, magpie, or raven, pleases call the number below promptly. Do not touch the bird. DHS will record all dead bird reports and will arrange for pickup and laboratory testing for WNV when appropriate.

Dead Bird Surveillance and Contact Information:
West Nile Virus Dead Bird Surveillance Program
Division of Communicable Disease Control
California Department of Health Services
Toll Free Telephone: 877-WNV-BIRD (877-968-2473)

Additional Information:

Migratory Birds - Flyway Map
(Migratory birds can expand endemic regions)

WNV Fly Pattern