West Nile Virus Neuroinvasive Disease

West Nile Virus (WNV) is a emerging or re-emerging mosquito-borne virus, increasingly present in most European countries.

Though most of the infected individuals are asymptomatic (80%) or develop a self-limited flu-like disease (20%), 1% will develop the severe form of West Nile Virus which is called West Nile Virus Neuroinvasive Disease (WNV NID)[1]. The case fatality rate in West Nile Virus Neuroinvasive Disease cases is approximately 10%, since patients with West Nile Virus Neuroinvasive Disease may have prolonged Intensive Care Unit (ICU) stays with considerable long-term morbidity and mortality[2].

West Nile Virus Neuroinvasive Disease manifests irtself as meningitis, encephalitis, Acute Flaccid Paralysis (AFP), or a combination of those.

West Nile Virus Neuroinvasive Disease is characterized by fever and signs of meningeal inflammation, such as nuchal rigidity, photophobia, and nausea and vomiting. West Nile Virus encephalitis is associated with prolonged altered mental status, seizures, or focal neurological signs.

Patients with severe West Nile Virus encephalitis may present with stupor or coma. Acute paralysis associated with West Nile Virus infection has been attributed to a poliomyelitis-like syndrome, myeloradiculitis, and Guillain–Barré Syndrome (GBS). West Nile Virus poliomyelitis with or without brainstem involvement is the most common neuromuscular manifestation of a West Nile Virus infection, resulting in asymmetric paralysis.

The motor neurons in the anterior horns and in the brainstem are the major sites of pathology responsible for neuromuscular signs; however, inflammation may also involve motor axons (polyradiculitis) and peripheral nerves (GBS). In comparison to patients with poliomyelitis-like syndrome, those resembling GBS have symmetric weakness with sensory loss.

No vaccine for humans is yet available. Horses can be vaccinated with a choice of vaccines.

[1] Santini et al: Severe West Nile Virus Neuroinvasive Disease: Clinical Characteristics, Short- and Long-Term Outcomes in Pathogens – 2022. See here.
[2] Sejvar: Clinical manifestations and outcomes of West Nile virus infection in Viruses – 2014. See here.