West Nile Virus Basics

• What is West Nile Encephalitis?

• How Serious is West Nile virus?

• Signs and Symptoms

• What is the risk of a West Nile Encephalitis outbreak in Minnesota?

• What can people do to prevent West Nile virus?

• How can I help look for west Nile virus?

Transmission

West Nile Virus is one of several mosquito-transmitted diseases that has been seen in Minnesota.

Signs and Symptoms

The typical incubation period for West Nile is 2-6 days, although it can be as long as 15 days.

• Most people infected with West Nile virus will be asymptomatic or experience a flu-like illness

• 20% of those bitten by an infected mosquito will develop the symptoms of West Nile fever

• 1 out of 150 symptomatic people will develop the more severe form of West Nile encephalitis

West Nile Fever

West Nile fever symptoms include:

• Sudden onset of high fever (usually >120°F)

• Severe headache

• Nausea

• Vomiting

• Sore throat

• Backache

• Joint pain

• Prominent muscle aches and weakness

• Prolonged fatigue

• Rash (more commonly associated with West Nile fever than encephalitis)

• Swollen lymph nodes

West Nile encephalitis

Less than 1% of those infected with West Nile will develop severe neurological symptoms consistent with encephalitis or meningitis.

West Nile encephalitis symptoms include:

• Mental status changes

• Vomiting

• Sensitivity to light

• Altered reflexes

• Seizures (less frequent)

• 15% progress to coma

• Acute flaccid paralysis (AFP) occurs in a small percentage of severely affected patients

The death rate among those showing symptoms of severe West Nile infection (encephalitis or meningitis) is around 10% and most severe cases are elderly people.

What is West Nile Encephalitis?

• West Nile Encephalitis is a viral disease transmitted to people and horses through the bite of an infected mosquito.

• West Nile virus is maintained in a transmission cycle involving one or more species of mosquitoes and birds. Current research is focusing on which mosquitoes and birds are most important in this cycle.

• West Nile Virus is usually found in Africa and southern Europe. The virus was first reported in North America during a 1999 outbreak of encephalitis in New York City.

How Serious is West Nile virus?

• Most people infected with West Nile virus will have either no symptoms or a very mild illness. A small percentage of people, especially elderly patients, may develop encephalitis (inflammation of the brain). Approximately 10% of these encephalitis cases are fatal.

• Most of the severe human cases of West Nile encephalitis begin with sudden onset of fever, headache, stiff neck, and vomiting. The illness progresses quickly to include confusion and other mental status changes, altered reflexes, convulsions, and coma. There is no treatment for West Nile encephalitis other than supportive care.

• Approximately 33% of symptomatic horses are put down or die from West Nile virus infections.

What is the risk of a West Nile Encephalitis outbreak in Minnesota?

Since 1999, West Nile virus has moved rapidly to 47 states, the District of Columbia, 75 Canadian Provinces, 24 Mexican States, Dominican Republic, El Salvador, Jamaica, and the Cayman Islands. West Nile virus was detected in Minnesota (July 23rd, 2002).

9,858 human West Nile cases were reported in the United States in 2003.

With our abundant mosquito and bird populations, we expect that West Nile virus will become established in Minnesota. Similar to other mosquito-transmitted diseases already established in this area (LaCrosse encephalitis, Western equine encephalitis, and Eastern equine encephalitis), West Nile virus will likely cause sporadic illness in humans (especially elderly people) and horses.

What can people do to prevent West Nile virus?

Personal protection measures such as use of mosquito repellents, avoiding outdoor exposures at dusk and dawn (peak feeding time for many mosquitoes), and wearing long-sleeved shirts and long pants can reduce the risk of West Nile encephalitis.

Removal of water-holding containers (mosquito breeding sites) from residential areas will reduce numbers of several mosquito species.

How can I help look for west Nile virus?

The first indication of West Nile virus in an area is usually an outbreak of the disease in wild bird populations. Over 255 species of birds have been found to be infected, but dead American crows and Blue Jays are especially apparent in outbreak areas. If you find dead birds during the summer months, please report them to the Minnesota Department of Health at 612-676-5055 or www.health.state.mn.us.