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Symptoms
West Nile Fever (WNF), which occurs in 20 percent of cases, is a febrile syndrome which causes flu-like symptoms.[5]WNF has an incubation period of two to eight days followed by fever, headache, chills, diaphoresis (excessive sweating), weakness, lymphadenopathy (swollen lymph nodes), drowsiness, pain in the joints and symptoms like those of influenza. Occasionally, some patients experience a short-lived truncal rash or gastrointestinal symptoms, including nausea, vomiting, loss of appetite, or diarrhea. Symptoms are generally resolved within seven to 10 days, although fatigue can persist for some weeks and lymphadenopathy up to two months.
West Nile Neuroinvasive Disease, which occurs in less than 1 percent of cases, is when the virus infects the central nervous system resulting in meningitis, encephalitis, meningoencephalitis or poliomyelitis.[6]
The more dangerous encephalitis is characterized by similar early symptoms, but also a decreased level of consciousness, sometimes approaching near-coma. Deep tendon reflexes are hyperactive at first, later diminished. There are also extrapyramidal symptoms. Recovery is marked by a long convalescence with fatigue. One study found that neuroinvasive WNV infection was associated with an increased risk for subsequent kidney disease.[7][8]
More recent outbreaks have resulted in a deeper study of the disease and other, rarer, outcomes have been identified. The spinal cord may be infected, marked by anterior myelitis with or without encephalitis.[9] WNV-associated Guillain-Barré syndrome has been identified[10] and other rare effects include multifocal chorioretinitis (which has 100% specificity for identifying WNV infection in patients with possible WNV encephalitis),[11] hepatitis, myocarditis, nephritis, pancreatitis, and splenomegaly.[12][13][14]