What are the symptoms of West Nile disease?

Symptoms of West Nile Virus Disease

Most West Nile virus infections are asymptomatic, but when symptoms occur, they typically range from mild flu-like illness to severe neurological manifestations including encephalitis, meningitis, and acute flaccid paralysis. 1

Clinical Presentation Spectrum

Asymptomatic Infection

• The majority of people infected with West Nile virus remain asymptomatic 2

Mild Illness (West Nile Fever)

• Sudden onset of high fever (up to 104°F/40°C)
• Severe headache
• Generalized myalgias (muscle pain)
• Lumbosacral pain
• Fatigue
• Anorexia
• Nausea and vomiting
• Dizziness
• Lymphadenopathy (swollen lymph nodes)
• Non-pruritic maculopapular rash 2, 3
• Bradycardia in relation to elevated body temperature (Faget's sign) 2

Neuroinvasive Disease

Occurs in approximately 1% of infected individuals with a 10% case-fatality rate 1

• Meningitis: Fever, headache, neck stiffness
• Encephalitis: Altered mental status, confusion, disorientation, coma
• Poliomyelitis-like acute flaccid paralysis: Weakness or paralysis of limbs 3, 4

Movement Disorders (Common during acute illness)

• Tremor (94% of patients with neuroinvasive disease)
• Myoclonus (31%)
• Parkinsonism features (69%) 4

Laboratory Findings

• Leukopenia (low white blood cell count) during the first week
• Leukocytosis (elevated white blood cell count) may occur during the second week
• Elevated liver enzymes
• In severe cases: bleeding abnormalities, decreased platelet count, elevated prothrombin and partial thromboplastin times 2

Disease Course and Timeline

• Incubation period: Usually 3-6 days after mosquito bite
• Initial phase: Acute febrile illness lasting approximately 3 days (viremic period)
• Recovery or progression: Many patients recover uneventfully, but approximately 15% may experience recurrence of more severe symptoms within 48 hours following the viremic period 2

Risk Factors for Severe Disease

• Advanced age (elderly patients)
• Immunocompromised status
• Pre-existing medical conditions 3, 5

Long-Term Outcomes

• Patients with meningitis or encephalitis may have favorable outcomes
• Persistent symptoms may include fatigue, headache, and myalgias
• Movement disorders may persist in some patients
• Patients with acute flaccid paralysis typically do not recover limb strength 4

Clinical Pitfalls and Diagnostic Challenges

• Symptoms are non-specific and can mimic other viral illnesses
• Maintain high index of suspicion during mosquito season, particularly in endemic areas
• Initial diagnosis of encephalitis and reporting of abdominal pain are associated with higher mortality 5
• Must be differentiated from other causes of viral encephalitis, meningitis, and febrile illnesses 2

Special Populations

• Pregnant women: Potential for vertical transmission (estimated 4%), with isolated reports of fetal neurological defects 1
• Elderly: Higher risk of severe disease and mortality

Early recognition of symptoms, especially neurological manifestations, is crucial for appropriate supportive care and monitoring for complications in West Nile virus infection.