West nile virus infection natural history, complications and prognosis
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Ammu Susheela, M.D. [2]
Overview
WNV is usually transmitted to humans by the culex mosquito after feeding on infected birds with high-level viremia. Following an incubation period of 2-14 day, untreated patients can remain asymptomatic or present with West Nile fever or with life-threatening neuroinvasive disease. Common complications of WNV infections include neurological impairment. The prognosis of mild disease is excellent; whereas West Nile meningitis and encephalitis may have residual neurologic deficits.
Natural History
WNV is a member of Japanese encephalitis antigenic complex of the family Flaviviridae. It is transmitted by a mosquito bite, most commonly Culex pipiens. Birds are the natural reservoir of the virus and the disease is generally transmitted to humans when a mosquito that previously fed on a bird with high-level viremia bites a human.[1]
Incubation Period
The incubation period for WNV disease is typically 2 to 6 days. It ranges from 2 to 14 days and can be several weeks in immunocompromised patients. An estimated 70-80% of human WNV infections are subclinical or asymptomatic. Less than 1% of infected individuals develop neuroinvasive disease, which typically manifests as meningitis, encephalitis, or acute flaccid paralysis.[2]
Asymptomatic West Nile Infection
When left untreated, approximately 80% of the people infected by virus remain asymptomatic.
West Nile Fever
Around 20% of the patients infected with WNV develop West Nile fever and usually present with fever and other constitutional symptoms. If left untreated, the infection generally self-resolves with no complications or sequelae.
Neuroinvasive Disease
Approximately 1 in 150 persons infected with WNV will develop a severe form of disease if left untreated. Serious illness can occur in patients of any age. However, advanced age, systemic diseases such as malignancy and cardiovascular disease, and immunosuppressed patients are considered high risk for developing neuroinvasive disease.
Possible complications
- Complications from mild West Nile virus infection are very rare.
- Complications from severe West Nile virus infection are as follows
Neurologic complications
- Meningitis
- Encephalitis
- Parkinsonism
- Rhomboencephalitis
- Cerebellar dysfunction
- West nile poliomyelitis [3]
- Dysphagia
- Permanent motor weakness
- Cranial nerve palsy
HEENT complications
Respiratory complications
Vascular complications
Other visceral organ complications
Prognosis
- In general, the prognosis of a mild WNV infection is excellent. Most patients with non-neuroinvasive WNV disease or WNV meningitis recover completely. However, fatigue, malaise, and weakness can linger for weeks or months.
- Patients who recover from WNV encephalitis often have residual neurologic deficits. Among patients with neuroinvasive disease, the overall case-fatality ratio is approximately 10%. The rate is significantly higher among patients with WNV encephalitis compared to patients with WNV meningitis.
References
- ↑ "West Nile Virus".
- ↑ "West Nile Virus".
- ↑ "Neurologic Complications of West Nile Virus".
- ↑ Perelman A, Stern J. "Acute pancreatitis in West Nile Fever." American Journal of Tropical Medicine and Hygiene 1974; 23: 1150-1152.
- ↑ Omalu B I, Shakir A A, Wang G, Lipkin W I, Wiley C A. "Fatal fulminant pan-meningo-polioencephalitis due to West Nile virus." Brain Pathology 2003; 13: 465-472
- ↑ Mathiot C C, Georges A J, Deubel V. "Comparative analysis of West Nile virus strains isolated from human and animal hosts using monoclonal antibodies and cDNA restriction digest profiles." Res Virol 1990; 141: 533-543.