WNV >  Information for Healthcare Professionals > Diagnosis & Treatment
Laboratory diagnosis

Usual laboratory findings:

  • normal or elevatel levels of white blood cells (lymphocytic predominance)
  • anaemia
  • hyponatremia (usually in encephalitis)
  • cerebrospinal fluid (CSF) findings: lymphocytic pleocytosis (findings are typical of a viral meningoencephalitis)
  • Computer tomography: does not facilitate diagnosis but can exclude other causes of meningitis/encephalitis
  • Magnetic Resonance Imaging: usually normal, sometimes with atypical findings (cerebrum signal lessions)

Laboratory examinations used for diagnosis:
The laboratory diagnosis is mainly based on the detection of WNV-specific IgM and increasing titres of IgG antibodies in serum and/or CSF.

Serological examination (ELISA/IFAT)
As IgM antibodies are not capable of passing the blood-brain barrier, when anti-WNV IgM antibodies are detected in CSF, the case is considered as confirmed WNV infection.

Disadvantages of serology:

- cross-reaction with other fliaviviruses
Plaque reduction neutralization test (PRNT) is used for differentiation of the antibodies produced against different flaviviruses, but it is time-consuming and it is performed only in reference laboratories

- persistence of WNV IgM antibodies (sometimes for more than one year) may cause problems in discriminating an acute from a previous infection
avidity tests usually enable the discrimination

Polymerase chain reaction (PCR) is not very helpful for the diagnosis of WNV infections due to low and short viremia in patients.
Nucleic acid testing (ΝΑΤ) is the method of choice for the screening of blood donors.

Virus isolation
Virus isolation, although the gold standard, is rarely used for diagnostic purposes; it is performed in reference laboratories and it is usually negative because of the short duration of viremia and the low titer of the virus in the bloodstream of WNV-infected patients.

Diagnostic criteria:
According to the Hellenic Center for Disease Control and Prevention (HCDCP), a patient is considered WNV infected when he/she meets one of the clinical AND one of the laboratory criteria.

Clinical criteria Laboratory criteria 
Encephalitis (disturbance of consciousness and fever)

Virus isolation/detection in blood or CSF or other tissue 

Aseptic meningitis 

Detection of WNV-specific IgM antibodies in CSF

Other acute clinical manifestations from the CNS or the peripheral nervous system (paresis, sensory disturbances, etc) 

High titers of IgM antibodies or increasing IgG antibody titer in consecutive serum samples 
Fever without clinical manifestations from the nervous system and absence of any other possible diagnosis

(Clinical specimens are sent to a Reference Laboratory for the appropriate examination)

Case classification:

Possible case: compatible clinical picture and high IgM antibody titer in serum or increasing IgG antibody titer in consecutive serum samples.

Confirmed case: compatible clinical picture and detection of IgM antibodies against WNV in CSF or isolation/detection of the virus in blood or CSF or other tissue.

**WNV infection should be included in the National Mandatory System. Healthcare professionals should be familiar with the case report form and the disease recording system of their country.


No specific treatment is available for WNV infection, and the care is supportive.

In severe cases, mainly those with WNND, hospitalization is required, while critically ill patients may need management in intensive care unit (respiratory support).

Interferon and ribavirin, usually used for the treatment of viral infections, have been tried only in vitro. Intravenous administration of human immunoglobulin seems to be effective for the treatment of WNV infection.

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