West Nile Virus

West Nile Virus (WNV) is caused by a mosquito transmitted virus (Arbovirus) that is carried by birds, especially magpies, crows and ravens. Other birds, mammals, reptiles, horses and humans can contract the virus through the bite of a WNV infected mosquito. West Nile virus has a complex lifecycle between certain birds and certain mosquito species. Some birds like crows, magpies, ravens, birds of prey, and sage grouse are highly susceptible to WNV and it is often fatal in these species.

Commonly Affected Species:

Signs Of Disease

Signs of WNV vary by depending on the species affected. Some birds carry the virus, remaining asymptomatic while some species are highly susceptible. Clinical signs can range from no reaction to the virus to mortality, especially in corvids (crows, ravens and magpies). Finding dead ravens, crows, magpies, and birds of prey may indicate WNV is present in an area. WNV has also affected sage grouse in some areas of Idaho and the intermountain west. Birds usually do not show any clinical signs when infected with WNV. Chickens can be infected with WNV and not become sick. However, natural disease due to the virus has been reported in domestic geese, ducks, pigeons and chickens.

Where is Disease Found?

West Nile Virus is native to the northern parts of Africa, the Middle East and occasionally southern Europe. After introduction to North America in 1999, the virus spread to every state and most of the southern provinces of Canada. The first detection of WNV in Idaho was in 2003 and the disease has been reported annually ever since.

How Can I Protect Myself?

In humans, 80% of WNV infections remain asymptomatic reactions. In the 20% of people who show symptoms of WNV infection, most present with the relatively mild fever and approximately 1% develop more serious nervous system problems and some may die. Avoiding mosquito bites is the most important aspect of protection for humans to avoid WNV. Humans should wear mosquito repellent containing DEET in accordance with the label, wear long-sleeved shirts and long pants, particularly during dusk and dawn when mosquitoes are most active, repair broken screens in houses, and reduce standing water around homes to reduce mosquito breeding habitat. Horses are susceptible to West Nile virus, but a vaccine is available and should be administered.

Samples to Collect

If there is concern about this condition, contact a conservation officer or an Idaho Department of Fish and Game Regional Office. Appropriate samples can be collected for testing if deemed necessary..

Can I Eat The Meat?

Meat from animals that are sick with or die from WNV should not be consumed by humans.

What is IDFG doing to help manage this disease?:

Currently IDFG is:

Working cooperatively with the Idaho Department of Health and Welfare and Idaho State Department of Agriculture to track dead birds and the occurrence of WNV in Idaho
Collecting and testing samples from dead corvids, sage grouse and raptors for WNV
Providing public education about WNV

How do I learn more about this disease?