Public - West Nile Virus Disease - Diagnosis

West Nile Virus Disease

Module information



		Prevention
		Screening
		Diagnosis
		Consultation for Diagnosis
		Hospitalization
		Non-drug Therapy
		Drug Therapy
		Patient Education
		Consultation for Management
		Follow-up

	Tables
	References
	Glossary
	What's New
	Patient Information
	Guidelines and Systematic Reviews

Diagnosis
Consider the diagnosis of WNV infection in patients with potential exposure and a compatible clinical presentation. Consider the diagnosis in a person who has been potentially exposed to mosquitoes and who presents with fever, headache, and myalgia, with or without gastrointestinal symptoms and skin rash, and especially if neck stiffness and/or a change in mental status and/or weakness is present. Collect historical information about conditions that may predispose the patient to a worse prognosis. Use physical exam findings to confirm meningitis, encephalitis, or acute flaccid paralysis and to prognosticate outcome. Confirm the diagnosis with a WNV-specific test, with acute and convalescent serology, by isolating the virus, or with amplification of WNV genomic sequences. Support the diagnosis of WNV encephalitis or other neuroinvasive syndromes with imaging studies. Support the diagnosis of WNV meningitis, encephalitis, or other neuroinvasive syndromes, or identify other associated clinical conditions, with appropriate blood studies. Support the diagnosis of WNV meningitis, encephalitis, or other neuroinvasive syndromes with CSF studies. Support the diagnosis of WNV encephalitis or other neuroinvasive syndromes with additional neurologic studies. Consider the broad differential diagnosis of WNV meningitis, encephalitis, and other neuroinvasive syndromes.
History and Physical Examination Elements for WNV Meningitis, Encephalitis, or Other Neuroinvasive Syndromes (table)
Laboratory and Other Studies for West Nile Viral Illnesses (table)
Differential Diagnosis of WNV Encephalitis, Meningitis, and Other Neuroinvasive Syndromes (table)


Consider the diagnosis of WNV infection in patients with potential exposure and a compatible clinical presentation.
Ask about: Known WNV activity, in humans, animals, or mosquitoes, in the area where the patient resides Travel to areas where activity or epidemics have been recognized Potential mosquito exposure for the patient Mosquito bites Mosquitoes seen inside home, work, or recreation environments Barrier methods (e.g., screens, long-sleeved shirts) and protective measures (e.g., DEET) Standing water around home or work Blood transfusions in the month before presentation Organ transplantation in the month before presentation See table History and Physical Examination Elements for WNV Meningitis, Encephalitis, or Other Neuroinvasive Syndromes.
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Consider the diagnosis in a person who has been potentially exposed to mosquitoes and who presents with fever, headache, and myalgia, with or without gastrointestinal symptoms and skin rash, and especially if neck stiffness and/or a change in mental status and/or weakness is present.
Ask about: Duration of symptoms Recent activity outside (especially during dawn or dusk) and possible exposure to mosquitoes Fever Headache Nausea Vomiting Diarrhea Abdominal pain Weakness Myalgia Confusion, disorientation, or personality change Rash See table History and Physical Examination Elements for WNV Meningitis, Encephalitis, or Other Neuroinvasive Syndromes.
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Collect historical information about conditions that may predispose the patient to a worse prognosis.
Note patient age, history of diabetes, or evidence of immunocompromise suggested by a history of disease, alcoholism, or corticosteroid or immunosuppressive therapy. See table History and Physical Examination Elements for WNV Meningitis, Encephalitis, or Other Neuroinvasive Syndromes.
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Use physical exam findings to confirm meningitis, encephalitis, or acute flaccid paralysis and to prognosticate outcome.
Look for: Fever (temperature >37.8°C) Signs of meningitis (nuchal rigidity) Signs of encephalitis (changes in mental status, weakness) Evidence of brainstem, cranial nerve, or cerebellar dysfunction Limb weakness See table History and Physical Examination Elements for WNV Meningitis, Encephalitis, or Other Neuroinvasive Syndromes.
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Confirm the diagnosis with a WNV-specific test, with acute and convalescent serology, by isolating the virus, or with amplification of WNV genomic sequences.
Demonstrate IgM by IgM antibody-capture ELISA, and/or Demonstrate four-fold increase in neutralizing antibody titers when comparing acute- and convalescent-phase serum samples (collected 7 to 14 days apart), and/or Amplify WNV nucleic acid sequence from tissue, blood, CSF, or other body fluid, and/or Isolate WNV by cell culture of tissue, blood, CSF, or other body fluid. Encourage autopsy in fatal cases to isolate virus and better characterize pathologic changes, especially in brain and spinal tissue. See table Laboratory and Other Studies for West Nile Viral Illnesses.
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Support the diagnosis of WNV encephalitis or other neuroinvasive syndromes with imaging studies.
Perform MRI of involved central nervous system components (e.g., brain and/or spinal cord) to exclude a diagnosis of HSV encephalitis and other infectious causes of encephalitis that have highly specific patterns on MRI. See table Laboratory and Other Studies for West Nile Viral Illnesses.
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Support the diagnosis of WNV meningitis, encephalitis, or other neuroinvasive syndromes, or identify other associated clinical conditions, with appropriate blood studies.
Perform CBC and blood chemistries to look for lymphocytopenia, anemia, thrombocytopenia, and/or hyponatremia. See table Laboratory and Other Studies for West Nile Viral Illnesses.
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Support the diagnosis of WNV meningitis, encephalitis, or other neuroinvasive syndromes with CSF studies.
Perform CSF cell counts and chemistries to detect pleocytosis and elevated protein with normal glucose. See table Laboratory and Other Studies for West Nile Viral Illnesses.
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Support the diagnosis of WNV encephalitis or other neuroinvasive syndromes with additional neurologic studies.
Obtain an EEG if HSV is being considered to look for localizing temporal lobe findings. Obtain an EMG and/or NCS if acute flaccid paralysis is present. See table Laboratory and Other Studies for West Nile Viral Illnesses.
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Consider the broad differential diagnosis of WNV meningitis, encephalitis, and other neuroinvasive syndromes.
When febrile illness progresses over several days with neurologic changes, especially when the findings are compatible with meningitis and/or encephalitis, consider the patient's age, immune status, comorbid conditions, and exposure history when considering the differential diagnosis, which includes Other North American flaviviruses (St. Louis encephalitis, Powassan fever), alphaviruses (Western and Eastern equine encephalitis), and bunyaviruses (La Crosse virus) Other infectious viral encephalitides, especially with foreign travel in the history (e.g., Japanese encephalitis virus in Asia and Murray Valley encephalitis virus in Australia) Other viruses (e.g., HIV, coxsackievirus, echovirus, enterovirus) Bacterial infections (e.g., Lyme disease, Leptospira) Tick paralysis Stroke Brain abscess or paraspinal epidural abscess Brain tumor See table Differential Diagnosis of WNV Encephalitis, Meningitis, and Other Neuroinvasive Syndromes.
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