West Nile Virus Workup

Updated: Mar 31, 2022
  • Author: Jess D Salinas, Jr, MD; Chief Editor: Elizabeth A Moberg-Wolff, MD  more...
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Laboratory Studies

See the list below:

  • The complete blood count (CBC) may show elevated or normal leukocytes values.

  • In cases of encephalitis, hyponatremia may be present. The complication of syndrome of inappropriate ADH (SIADH) secretion is a possibility.

  • Cerebrospinal fluid (CSF) analysis may reveal elevated protein and increased leukocyte levels, with predominant lymphocytes. [29, 30] Glucose levels are usually normal rather than decreased.

  • Serologic testing to detect immunoglobulin M (IgM) antibodies is currently the best means [4] of diagnosing West Nile virus infection.

    • IgM antibody-capture enzyme-linked immunosorbent assay (MAC-ELISA) has been used to detect IgM for the West Nile virus by using serum or CSF samples. [2, 31]

    • False-positive results may occur because of the close relationship of the West Nile virus to other flaviviruses.

    • In light of this limitation, the plaque reduction neutralization test (PRNT) may help to identify false-positive MAC-ELISA results caused by cross-reactions by other flaviviruses.


Imaging Studies

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  • In acute disease, computed tomography (CT) scans do not show any evidence of abnormalities.

  • In an estimated one third of infected individuals, magnetic resonance imaging (MRI) scans show notable enhancement in the leptomeninges and periventricular areas.


Histologic Findings

Autopsy findings in some patients with West Nile virus infection reveal mononuclear inflammation that extensively involves the medulla, with some involvement of the cranial nerve roots. [32] However, these findings are not diagnostic for the infection.