West Nile Virus

The Twin Cities' Source for Local Information About West Nile Virus


What is West Nile Virus?

How is it Transmitted?

How is it Measured in the Environment?

How is it Measured and Tracked?

Laboratory Evaluation

Molecular Actions of the Virus

Symptoms and Target Organs

What's New for Health Professionals?

How Is It Transmitted?

\People become infected with the virus when bitten by an infected mosquito. People and horses serve as incidental or dead end hosts. The primary infection spreads between a wide variety of mosquito species and bird species.

How do the mosquitoes get the virus?

Mosquitoes that bite infected birds or other mammals become infected. The virus may circulate in the mosquito’s blood for a few days. The virus is located in the salivary glands of the mosquitoes, and it is transmitted to people when the mosquito bites to take in blood.

What kind of mosquito carries this infection? Are they in Minnesota?

Yes, there are mosquitoes infected with WNV throughout Minnesota, including our seven county metro area. There are likely several species of mosquitoes infected, and the Metropolitan Mosquito Control Department is in the midst of their investigation to determine which species are carrying the infection.

Are there certain times of the day when I am more likely to get bitten by mosquitoes carrying this infection?

That depends on the species of mosquito carrying the virus. Most mammal feeding mosquitoes bite at dawn and dusk, but the tree hole mosquito, which also may carry the virus is a daytime feeder.

I’ve been bitten by lots of mosquitoes this summer and fall. What are my chances of getting sick?

Very slim. It is estimated that less than 1% of mosquitoes carry the virus, even during an active infection cycle. The transmission rate from an infected mosquito to a human is unknown, but even if the virus is successfully transmitted, the chance of becoming seriously ill with encephalitis is less than 1 in 150. There is a slightly larger chance you could get a flu like illness, but the vast majority of people infected with the virus show no signs at all.

If someone in my family has the infection, can I catch it?

WNV is not spread person to person.

Can I get sick from touching birds? What about dead birds?

There is no evidence to date of infection from handling dead or infected birds. If you find a dead bird, however, use gloves to handle it and place the dead bird in a plastic bag before disposing of it. Contact your county health department for directions on how to safely dispose of the dead bird. Click here for a form to report dead bird sightings to the Minnesota Department of Health.

Can I get the virus any other way?

WNV has been successfully transmitted from an infected organ donor to four organ recipients. In addition, there are other cases of persons becoming ill with WNV after receiving blood transfusions, which are under investigation/ There has also been a case report of transmission of WNV via breast milk, although no illness resulted..

Is there a way to test blood or transplant organs for the infections?

To date there is no test to screen donated blood. Persons who have had recent symptoms consistent with West Nile Fever should not be allowed to donate blood.

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