West Nile Virus
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Update: West Nile virus (WNV) has been confirmed in birds in Washtenaw County, including on the UM campus. Human cases of WNV have been confirmed in Michigan. For more information, see More Resources.
What is West Nile virus? West Nile virus (WNV) can cause encephalitis (an inflammation of the brain) in humans. It is believed to have found its way into the eastern United States in 1999 or before. Prior to 1999, no cases occurred in the US among persons without recent travel outside the US.
How is West Nile virus transmitted?
The virus is not transmitted from person-to-person. You cannot get it from touching or kissing a person who has the virus or from a health care worker who has treated someone with it.
Birds are the primary host for the virus (they may also become sick) and mosquitoes are the vectors that transmit it. Humans and livestock are incidentally infected. Horses are at risk of severe disease, too.
Mosquitoes become infected with West Nile virus when they feed on infected birds that carry the virus in their blood. Mosquitoes' salivary glands become infected and those infected mosquitoes can then transmit the virus to humans and other animals while biting them to take blood. During blood feeding, the mosquito injects the virus into the animal or human, where it multiplies and may cause illness.
Can I get West Nile virus directly from birds?
Crows and some other animals are susceptible to infection with West Nile virus. However, there is no evidence that a person can get the virus from handling live or dead infected birds or other animals. However, people should avoid bare-handed contact with any dead animals and use gloves or double plastic bags to pick up the carcass and place it in a container.
Should dead birds be reported?
Because birds are a key link in the transmission of the disease, individuals are encouraged to report dead ravens, crows and blue jays in Michigan. If these dead birds are found on the UM campus, contact UM Plant Services at 734-647-2059 for pick up and reporting. In Michigan, you can report a dead bird via the Michigan website on West Nile virus or via your local health department (see Washtenaw County website for further information).
A Michigan hotline provides recorded instructions for collecting dead birds at 888-668-0869.
Surveillance for infected horses is also occurring.
What are symptoms in people?
Most people infected with the West Nile virus have no symptoms of illness.
Approximately 20% of those infected develop a mild illness with fever, headache and body aches, sometimes with skin rash and swollen lymph glands. The incubation period after the bite of an infected mosquito is thought to range from 3 to 14 days, and symptoms generally last 3 to 6 days.
Encephalitis is less common, affecting approximately 1 out of every 150 infected individuals. Symptoms of encephalitis may include headache, high fever, stiff neck, change in mental status, disorientation, coma, tremors, convulsions, muscle weakness and paralysis. In a few cases, mostly among the elderly, death may occur.
If you have symptoms of encephalitis, call or visit your clinician as soon as possible for assessment. For more information about using UHS, see Schedule an Appointment.
If I live in an area where birds or mosquitoes are infected and a mosquito bites me, am I likely to get sick?
No. Even in areas where mosquitoes carry the virus, very few mosquitoes (much less than 1%) are infected. If a mosquito is infected, less than 1% of people who get bitten and become infected will get severely ill. The chances that you will become severely ill from any one mosquito bite are extremely small.
What proportion of people with severe illness due to West Nile virus die?
Among those with severe illness due to West Nile virus, case-fatality rates range from 3-15% and are highest among the elderly. Less than 1% of those infected with the virus will develop severe illness.
Prevention: There is no human vaccine for West Nile encephalitis, but you can reduce the risk of infection in the following ways:
- Avoid situations where you will be exposed to mosquitoes.
- Apply insect repellent that contains the active ingredient DEET to exposed skin. Follow the manufacturer's directions for use on the label.
- Spray clothing with repellents containing permethrin or DEET because mosquitoes may bite through thin clothing. Follow the manufacturer's directions for use on the label.
- Avoid applying repellent to children under 2 years of age and to the hands of older children because repellents may irritate the eyes and mouth.
- Wear long-sleeved shirts and long pants when outdoors.
- Maintain window and door screening to keep mosquitoes out of buildings.
- Empty water from mosquito breeding sites, such as flower pots, pet bowls, clogged rain gutters, swimming pool covers, discarded tires, buckets, barrels, cans and similar sites in which mosquitoes can lay eggs.
