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West Nile Encephalitis (cont.)

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What is the incubation period for a West Nile virus infection?

The incubation period (the time from infection to the development of symptoms) is five to 15 days.

What are West Nile virus infection symptoms and signs?

Mild or symptom-free infections are common with the West Nile virus. Among all people who become infected, only two out of 10 develop any symptoms. Of those, most only have mild symptoms similar to those of the flu, such as headache, body aches, joint pain, swollen lymph nodes, vomiting, diarrhea, or rash. The symptoms are not severe enough for most people to seek medical care, but tiredness and weakness can last for several weeks. Typically, only one in 150 infections lead to severe or neuroinvasive (nervous system disease) infections, according to the CDC. Neuroinvasive disease is caused by infection and inflammation of the surface covering of the brain (meningitis) or deeper infection of the brain itself (encephalitis).

Neuroinvasive disease is uncommon but more likely to occur in those over age 50. There are two general symptoms of neuroinvasive disease. Meningitis is marked by headache, high fever, and neck stiffness. Encephalitis causes these symptoms but may progress to stupor (sleepiness), disorientation, hallucinations, paralysis, coma, tremors, convulsions, and rarely death. Sometimes general weakness progressing to complete paralysis occurs, similar to polio; this is called acute flaccid paralysis.

West Nile virus can have some long-term effects after severe illnesses. West Nile virus meningitis or encephalitis may result in a prolonged recuperation and rehabilitation period, especially in the elderly. Memory loss, depression, irritability, and confusion are the most prevalent residual effects.

Patients may also experience difficulty walking, muscle weakness, joint pain, fatigue, vomiting, diarrhea, and insomnia.

Symptoms in children and babies are basically the same as symptoms in adults. Children may complain of headache, may have a fever, and may become lethargic.

Since most cases of West Nile virus infection are mild, the prognosis for recovery is generally good. In severe cases, death rates are highest in the elderly.

Medically Reviewed by a Doctor on 10/16/2017


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