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]Centers for Disease Control and Prevention. West Nile virus: clinical signs and symptoms of West Nile virus disease. May 2024 [internet publication].
https://www.cdc.gov/west-nile-virus/hcp/clinical-signs/index.html
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]Sejvar JJ, Haddad MB, Tierney BC, et al. Neurologic manifestations and outcome of West Nile virus infection. JAMA. 2003;290:511-515. Erratum in: JAMA. 2003;290:1318.
http://jama.ama-assn.org/cgi/content/full/290/4/511
http://www.ncbi.nlm.nih.gov/pubmed/12876094?tool=bestpractice.com
Overall case fatality rates for patients hospitalised for infection range from 4% to 18%.[5]Nash D, Mostashari F, Fine A, et al. The outbreak of West Nile virus infection in the New York City area in 1999. N Engl J Med. 2001;344:1807-1814.
http://www.nejm.org/doi/full/10.1056/NEJM200106143442401#t=article
http://www.ncbi.nlm.nih.gov/pubmed/11407341?tool=bestpractice.com
[46]Pepperell C, Rau N, Krajden S, et al. West Nile virus infection in 2002: morbidity and mortality among patients admitted to hospital in southcentral Ontario. CMAJ. 2003 May 27;168(11):1399-405.
http://www.ncbi.nlm.nih.gov/pubmed/12771068?tool=bestpractice.com
[81]Chowers MY, Lang R, Nassar F, et al. Clinical characteristics of the West Nile fever outbreak, Israel, 2000. Emerg Infect Dis. 2001;7:675-678.
http://www.ncbi.nlm.nih.gov/pubmed/11585531?tool=bestpractice.com
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]Hart J Jr, Tillman G, Kraut MA, et al. West Nile virus neuroinvasive disease: neurological manifestations and prospective longitudinal outcomes. BMC Infect Dis. 2014 May 9;14:248.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4020876
http://www.ncbi.nlm.nih.gov/pubmed/24884681?tool=bestpractice.com
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]Centers for Disease Control and Prevention. West Nile virus: possible persistence of West Nile virus infection. May 2024 [internet publication].
https://www.cdc.gov/west-nile-virus/hcp/clinical-signs/possible-persistence.html