West Nile Virus Infection

West Nile virus (WNV) is a mosquito borne flavivirus transmitted by Culex species, with birds as the amplifying hosts.

• Widely distributed in Africa, Europe, Middle East, Asia, Australia (Kunjin), and North America.
• About 80% of infections are asymptomatic; 20% develop West Nile fever; under 1% develop neuroinvasive disease.
• Risk factors for neuroinvasive disease: age over 60, diabetes, hypertension, chronic kidney disease, organ transplantation, and immunosuppression.
• Case fatality in neuroinvasive disease is about 10%; transmitted rarely via blood, organ transplantation, and congenitally.

• West Nile fever: fever, headache, myalgia, fatigue, rash (20 to 50%), and lymphadenopathy, lasting days to weeks.
• Neuroinvasive disease: meningitis (fever, neck stiffness), encephalitis (confusion, tremor, parkinsonism, seizures, coma), acute flaccid paralysis (poliomyelitis like asymmetric weakness), and rarely Guillain-Barre syndrome.
• Ocular: chorioretinitis, and optic neuritis.
• Long term fatigue, cognitive deficits, and motor weakness persist for months.

• WNV IgM in serum or CSF (ELISA; cross reaction with other flaviviruses, so plaque reduction neutralisation tests are needed to confirm), and RT-PCR (low sensitivity after viraemia clears).
• CSF: lymphocytic pleocytosis, elevated protein, normal glucose.
• MRI brain (T2/FLAIR hyperintensity in thalamus, basal ganglia, brainstem) and EMG/nerve conduction for flaccid paralysis.
• Exclude HSV encephalitis, Japanese encephalitis, dengue, St Louis encephalitis, enteroviruses, bacterial meningitis, and Guillain-Barre syndrome.

• Supportive care only; there is no approved antiviral or vaccine for humans.
• West Nile fever: analgesia, antipyretics, hydration.
• Neuroinvasive disease: ICU for respiratory failure from encephalitis or flaccid paralysis (ventilation), seizure control (levetiracetam), intracranial pressure management, and nutrition.
• IVIG, interferon, and corticosteroids have been tried without confirmed benefit.
• Rehabilitation (physiotherapy, occupational therapy) for paralysis and cognitive deficits.
• Prevention: mosquito control, repellents (DEET 20 to 30%), screens, blood donor screening, and reporting to public health authorities.