What is the severity of West Nile virus (WNV) infection?

West Nile Virus Infection: Severity and Clinical Impact

West Nile virus (WNV) infection is primarily asymptomatic in 70-80% of cases, but can cause severe neuroinvasive disease in approximately 1% of infected individuals, with a 10% case-fatality rate among those with neurological manifestations. 1

Clinical Spectrum of WNV Infection

WNV infection presents along a spectrum of severity:

• Asymptomatic infection (70-80%): Most infected individuals never develop symptoms 1

• Mild febrile illness (20-30%):

  • Fever and flu-like symptoms
  • Self-limiting course

• Neuroinvasive disease (<1%):

  • Encephalitis
  • Meningitis
  • Acute flaccid paralysis
  • Case-fatality rate of 10% 2

Risk Factors for Severe Disease

The risk of developing neuroinvasive disease increases significantly with:

• Age: Highest incidence (1.22 cases per 100,000) and mortality in adults ≥70 years 1
• Immunocompromised status: Particularly those with impaired cell-mediated immunity 3
• Gender: Males appear to have better recovery from coma than females 4
• Presentation with coma and cranial nerve deficits: Associated with poorer cognitive recovery 4

Neurological Manifestations and Long-term Outcomes

Neurological manifestations are the most concerning aspect of WNV infection:

• Initial presentation: 93% of neuroinvasive cases present with significant neurological deficits 4

  • Weakness (49%)
  • Tremor (35%)
  • Cranial neuropathy (16%)

• Long-term sequelae: Many patients who recover from neuroinvasive disease experience persistent symptoms 5

  • Weakness
  • Fatigue
  • Cognitive problems
  • Persistent tremors (58% of those initially affected) 4

Special Populations

Pregnant Women

Data on WNV infection during pregnancy is limited and somewhat ambiguous:

• Potential for vertical transmission (estimated at 4%) 2
• Case reports of severe maternal symptoms including fever, nausea, meningism, and seizures 2
• Isolated reports of fetal neurological defects including chorioretinitis, white matter loss, and cystic modifications 2

Diagnostic Approach

Laboratory diagnosis of WNV typically involves:

• Serology: Detection of WNV-specific IgM and/or IgG antibodies in serum and/or CSF 2

  • IgM antibodies detectable 3-8 days after symptom onset
  • IgM in CSF strongly suggests CNS infection

• NAAT (Nucleic Acid Amplification Test): More sensitive in immunosuppressed patients 2

  • Specimens: CSF, plasma, serum

Prevention and Management

Unfortunately, there are currently no approved vaccines or specific antiviral treatments for WNV infection 5:

• Prevention: Focuses on mosquito control and personal protective measures

  • Community-level mosquito control programs
  • Use of insect repellents
  • Wearing long sleeves and pants
  • Avoiding outdoor activities during peak mosquito hours

• Treatment: Supportive care is the mainstay of management

  • Empiric treatment with acyclovir may be initiated while awaiting diagnostic confirmation in cases of suspected viral encephalitis 2
  • Ribavirin is not recommended based on studies showing potential harm 2

Conclusion

WNV infection represents a significant public health concern with the potential for severe neurological complications, particularly in older and immunocompromised individuals. While most infections are asymptomatic or mild, the risk of severe disease with long-term neurological sequelae makes prevention crucial, especially for vulnerable populations.