A catch basin in Saint Paul, MN, a common breeding habitat for Culex mosquitoes, the carriers of WNV.

West Nile Virus

West Nile Virus (WNV) is the most common mosquito-borne disease found in Minnesota. The primary disease-carrying species are Culex pipiens, Culex restuans, and Culex tarsalis. MMCD works closely with the Minnesota Department of Health to monitor cases of WNV in Minnesota.

WNV Transmission Cycle

The West Nile Virus transmission cycle.

WNV normally cycles among birds and mosquitoes. The virus circulates in the blood of birds for a few days after infection. Mosquitoes acquire the virus when they feed on infected birds. Infected mosquitoes can then transmit West Nile virus to humans and animals through their bites. The virus is injected from the mosquito’s salivary glands into the blood stream where it can multiply and cause illness. Humans and animals are considered "dead end hosts" because the virus cannot be further transmitted once it reaches these hosts.

All residents of areas where West Nile virus activity has been identified and all visitors to those areas are at risk of West Nile virus infection. People who are over the age of 50 are at greatest risk of developing severe illness after exposure to West Nile virus. infection with West Nile virus is rare and 805 of people infected experience no symptoms of illness.

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How MMCD monitors disease vector mosquitoes and tests them for West Nile Virus

Symptoms and Prevention of West Nile Virus

Most WNV infections are mild, symptoms include fever, headache, and body aches, occasionally with a skin rash and swollen lymph glands. More severe infection may be marked by headache, high fever, neck stiffness, stupor, disorientation, tremors, convulsions, muscle weakness, paralysis, coma, and in 10% to 15% of severe cases, death. Only 1 out of 150 people infected with WNV develop a serious illness.

What should I do if I think I have West Nile Virus?

Please contact your health care provider. If you or your family members develop symptoms such as high fever, confusion, muscle weakness, and severe headaches, you should seek immediate medical attention.

Prevention of West Nile encephalitis and interruption of West Nile virus transmission is most effectively accomplished through integrated vector management programs like those employed by MMCD. MMCD is working closely with the Minnesota Department of Health to detect and control West Nile virus. This includes surveillance for West Nile virus activity in mosquitoes, birds, horses, other animals, and humans. Also important are implementation of appropriate mosquito control measures to reduce mosquito populations and public notification efforts. MMCD provides mosquito control services in the seven county metropolitan area and we work with MDH to keep the public informed of the current West Nile virus situation.

Below are some tips for avoiding mosquito bites: 

  • Stay indoors at dawn and dusk when most mosquitoes are active.
  • Wear loose-fitting long-sleeved shirts and long pants whenever you are outdoors.
  • Apply an EPA-registered insect repellent to exposed skin.
  • Remove any water-holding containers from your property, as they can produce mosquitoes.
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Get more tips to protect yourself and your home from mosquitoes in the MMCD Resident's Guide

Frequently Asked Questions

1Is there a vaccine against West Nile encephalitis?
There is currently no WNV vaccine available for humans.
2How is West Nile encephalitis treated?
There is no treatment for the viral infection itself. In severe cases, intensive supportive therapy is required. This may include hospitalization, intravenous fluids, airway management, respirator support, prevention of secondary infections, and nursing care.
3Can birds become infected with WNV?
WNV has been detected in over 320 bird species, but most species present with little or no illness. However, mortality rates are high in crows, blue jays, and some birds of prey.
4Can I get WNV from birds?
There is no evidence to date suggesting that humans can get West Nile virus from touching sick or dead birds. However, it is strongly recommended, for sanitary reasons, that you use protective gloves or a plastic bag when handling any sick, injured, or dead bird.
5Can horses become infected with WNV?
Yes, in the same way that humans can - through the bite of a mosquito. Most horses infected with West Nile virus recover, but for horses that develop severe symptoms mortality rates have ranged from 30% to 40% in the United States.
6How I can protect my horses from becoming infected with WNV?
A West Nile virus vaccine for horses is available. Proper inoculation requires at least two doses of the vaccine, so it is important to schedule vaccination prior to elevated mosquito activity. Contact your veterinarian for more details.
7Can WNV infect dogs or cats? Can they transmit the virus to me or my other pets?
Dogs and cats can become infected with West Nile virus in the same way as humans, horses, and birds; by the bite of an infectious mosquito. Illness in dogs and cats is extremely rare. There is no documented evidence of direct transmission of the virus to people from infected animals or to pets from another infected animal.

West Nile Virus Resources: