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Bureau of Disease Control

West Nile virus, Eastern Equine Encephalitis virus & St. Louis Encephalitis virus

What are the symptoms?

  • West Nile Virus
    Most people infected with West Nile Virus have no symptoms of illness. In some people, about 25% of those infected may have a mild illness that includes fever, headache and body ache, sometimes accompanied by a rash or swollen lymph glands.
    In less than 1% of the people infected, the severe form of encephalitis will be experienced. Symptoms of the encephalitis could include high fever, convulsions, stiff neck, tremors, headache, coma, stupor, disorientation, muscle weakness or paralysis. In a very few cases, mostly among the elderly, death may occur.
  • Eastern Equine Encephalitis
    Most people infected with Eastern Equine Encephalitis have no symptoms or mild flu-like symptoms. More severe infection is marked by sudden headache and high fever, followed by seizures and coma.
  • St. Louis Encephalitis
    Most people infected with St. Louis Encephalitis have no symptoms or mild flu-like symptoms. More severe infection is marked by sudden headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, occasional convulsions (especially in infants) and spastic (but rarely flaccid) paralysis.

How long does it take from the time of infection until symptoms begin?

  • West Nile Virus - 3-15 days
  • Eastern Equine Encephalitis - 5-15 days
  • St. Louis Encephalitis - 5-15 days

How is it treated?

  • West Nile Virus
    There is no specific cure for West Nile Virus. In mild cases, you should use the same remedies you would for other virus, such as the flu: drink plenty of water, resting in bed, drinking plenty of fluids, and taking medication such as ibuprofen or acetaminophen to relieve fever and discomfort. In more severe cases treatment may include hospitalization, respiratory support and intravenous therapy.
    Anyone experiencing severe or unusual headaches should see a doctor as soon as possible. Also, anyone who has been in an area where the virus has been identified and who experiences high fever, muscle weakness, confusion or severe headaches should see a doctor immediately.
  • Eastern Equine Encephalitis
    There is no specific treatment of cure for Eastern Equine Encephalitis except for supportive therapy.
    Anyone experiencing severe or unusual headaches should see a doctor as soon as possible. Also, anyone who has been in an area where the virus has been identified and who experiences high fever, muscle weakness, confusion or severe headaches should see a doctor immediately. The fatality rate among those with severe symptoms can be as high as 50%.
  • St. Louis Encephalitis
    There is no specific treatment of cure for St. Louis Encephalitis except for supportive therapy.
    Anyone experiencing severe or unusual headaches should see a doctor as soon as possible. Also, anyone who has been in an area where the virus has been identified and who experiences high fever, muscle weakness, confusion or severe headaches should see a doctor immediately. Case fatality rates can range from 3%-30% and are highest among the elderly.

What causes it?

  • West Nile Virus
    West Nile encephalitis cannot be passed from person to person. The only way to get the virus is from the bite of an infected mosquito.
    The virus actually starts with a bird, usually a crow. It spreads when a mosquito bites a bird that has the virus in their blood. The mosquito then can spread the virus to other birds, animals or people, when it bites during feeding. In areas where the virus has been identified, very few, much less than 1%, of the mosquitoes are infected.
  • Eastern Equine Encephalitis
    Eastern Equine Encephalitis cannot be passed from person to person. The only way to get the virus is from the bite of an infected mosquito.
    This is a relatively rare but very serious virus with only 153 confirmed cases in the US since 1964.
    The virus actually starts with a bird. It spreads when a mosquito bites a bird that has the virus in their blood. The mosquito then can spread the virus to other birds, animals or people, when it bites during feeding.
  • St. Louis Encephalitis
    St. Louis Encephalitis cannot be passed from person to person. The only way to get the virus is from the bite of an infected mosquito.
    St. Louis Encephalitis is the most common human disease caused by mosquitoes in the US.
    The virus actually starts with a bird. It spreads when a mosquito bites a bird that has the virus in their blood. The mosquito then can spread the virus to other birds, animals or people, when it bites during feeding

Who is most a risk from this disease?

  • West Nile Virus -
    People over 50 years old.
  • Eastern Equine Encephalitis -
    Residents of areas where the virus has been identified and those people who spend extended periods of time outdoors.
  • St. Louis Encephalitis
    Elderly, people working in outdoor occupations and anyone with stagnant water near their home. There are, on average, 128 cases of SLE reported each year in the US.

What can people do to avoid these infections?

  • West Nile Virus
    Mosquito control is key in reducing the impact of West Nile virus.
  • Eastern Equine Encephalitis
    Mosquito control is key in reducing the impact of Eastern Equine Encephalitis.
  • St. Louis Encephalitis
    Mosquito control is key in reducing the impact of St. Louis Encephalitis.