From the Guidelines
West Nile virus infection typically presents with a spectrum of clinical features ranging from asymptomatic infection to severe neuroinvasive disease, with myoclonus being a distinctive feature, as seen in flaviviruses, such as West Nile virus and Japanese encephalitis virus 1.
Clinical Features
The clinical features of West Nile virus infection can be categorized into several groups:
- Asymptomatic infection: Most infected individuals (about 80%) remain asymptomatic
- West Nile fever: Approximately 20% develop West Nile fever, characterized by fever, headache, body aches, joint pain, vomiting, diarrhea, and fatigue
- Neuroinvasive disease: Less than 1% of infected people develop neuroinvasive disease, which can manifest as:
- Meningitis (with neck stiffness, photophobia, and heightened sensitivity to sound)
- Encephalitis (with altered mental status, confusion, disorientation, coma, and seizures)
- Acute flaccid paralysis resembling polio
Risk Factors
Risk factors for severe disease include:
- Older age (over 60)
- Immunosuppression
- Certain chronic medical conditions
Diagnosis and Treatment
Symptoms typically appear 2-14 days after infection through a mosquito bite. Treatment is supportive as no specific antiviral therapy exists. The disease's severity stems from the virus's ability to cross the blood-brain barrier and directly infect neurons, causing inflammation and neuronal damage. Recovery from severe disease may be prolonged, with some neurological effects potentially becoming permanent.
Key Considerations
It is essential to consider West Nile virus infection in the differential diagnosis of patients presenting with encephalitis, particularly those with a history of mosquito exposure or residence in areas where the virus is endemic 1.
From the Research
Clinical Features of West Nile Virus
The clinical features of West Nile virus (WNV) infection can vary from asymptomatic to severe neuroinvasive disease, including:
- Encephalitis: inflammation of the brain, resulting in high fever, headache, neck stiffness, disorientation, tremors, seizures, and paralysis 2
- Meningitis: inflammation of the membranes surrounding the brain and spinal cord 2, 3
- Acute flaccid paralysis: a sudden onset of muscle weakness or paralysis, which can progress rapidly 4, 5, 6
- West Nile fever: a mild febrile illness, which can vary greatly in clinical severity and may be prolonged 3
Neuroinvasive Disease
Neuroinvasive disease, including encephalitis, meningitis, and acute flaccid paralysis, develops in less than 1% of WNV infections, but carries a fatality rate of approximately 10% 3. The spectrum of clinical presentations of acute flaccid paralysis in WNV infection can range from single extremity paralysis to quadriparalysis with cranial nerve involvement 5.
Other Clinical Features
Other clinical features of WNV infection may include:
- Respiratory failure: commonly develops in patients with acute flaccid paralysis 5
- Bladder dysfunction: occurs in approximately 22% of patients with acute flaccid paralysis 5
- Ophthalmoplegia: a rare manifestation of WNV infection, characterized by weakness or paralysis of the eye muscles 6
- Fever: nearly universal in patients with acute flaccid paralysis 5
- Signs of meningismus: less common in patients with acute flaccid paralysis 5