West Nile virus originated in Africa and was first seen in the U.S. in New York in 1999.
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It has now been detected in all 48 continental states.
It is more common in states with warmer climates.
Dr. Pollack says most infections occur between July - September.
The virus exists mainly in birds and is spread to humans via mosquito bites.
Dr. Pollack says the infection usually begins 2 - 14 days after exposure.
He says most people infected with West Nile virus are asymptomatic (have no symptoms).
Dr. Pollack says only 20 - 40% of people will have any symptoms.
He says the most common infection caused by West Nile virus is West Nile fever.
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- Fever, headache, fatigue, back pain, muscle pain, and loss of appetite are the most common symptoms.
- Eye pain, sore throat, nausea, vomiting, diarrhea, and abdominal pain can also occur.
- Symptoms typically last 3 - 10 days, but can persist longer.
- Rash appears in approximately 25 - 50% of patients with West Nile fever.
Dr. Pollack says about 1 out of every 200 people who are infected with the virus may get more severe neuroinvasive disease, such as meningitis, encephalitis, or flaccid paralysis.
He says risk factors for developing neuroinvasive disease include advanced age, cancer, and decreased immune function.
Dr. Pollack says neuroinvasive disease presents as fever with meningitis, encephalitis, or flaccid paralysis.
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Symptoms may also include headache, neck pain/stiffness, vomiting, eye sensitivity to light, confusion, or tremor.
- Meningitis occurs more commonly in children.
- Encephalitis is more common than meningitis in older age groups.
- Neuroinvasive disease can be very serious or even fatal.
Dr. Pollack says the diagnosis is made by testing for antibodies to West Nile virus in the blood and spinal fluid, but this is only necessary in very ill patients.
He says as with most viral illnesses; treatment is supportive care with pain and fever medicine, fluids, and rest. There is no cure.
Dr. Pollacka says prevention involves avoiding mosquito bites with long clothing and insect repellent and community mosquito control programs.