Prognosis

Most cases of West Nile fever resolve spontaneously and completely. However, symptoms such as fatigue, headache, weakness, movement disorders, and concentration problems may persist for weeks or months.[21]

Severe neuroinvasive disease can result in death or permanent disability. Mortality usually results from progressive neuronal dysfunction, cerebral oedema, and respiratory failure. West Nile meningitis tends to be self-limiting with a good prognosis. In contrast, West Nile encephalitis and West Nile poliomyelitis carry a much poorer prognosis as most people have long-lasting (>1 year) neurological problems.[40] Overall case fatality rates for patients hospitalised for infection range from 4% to 18%.[5][46]​​[81]​​

A study of prospectively-acquired neurological outcomes data among 55 patients with neuroinvasive disease in the US found that 93% of patients presented with significant neurological deficit on initial clinical examination including weakness (49%), cognitive impairment (45%), tremor (35%), coma (25%), and cranial neuropathy (16%). By the end of the 90-day follow-up, 33% of patients had returned to normal neurological function. The mortality rate in this study was 13%, with 5 of the 7 patients who died presenting with coma.[82]

In some patients, West Nile virus may persist in the kidneys after initial infection. It is currently unknown whether this can cause kidney disease or hypertension. Further research is required.[83]

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