West Nile Virus (And Other Arbovirus Encephalitis)

West Nile Virus (And Other Arbovirus Encephalitis): Excerpt from The 5-Minute Pediatric Consult

Jason Newland, MD

West Nile Virus - BASICS

West Nile Virus - description

• Viruses transmitted by an arthropod vector that can cause CNS infections and hemorrhagic fevers.
• Most arboviral infections are asymptomatic
• West Nile virus (WNV) is an arbovirus in the flavivirus family.
• WNV was 1st recognized in the US in 1999 during an outbreak of encephalitis in New York City.
• Other arboviruses can produce similar syndromes or acute hemorrhagic fevers.

West Nile Virus - general prevention

• Public health department efforts focus on surveillance of viral activity to predict and prevent outbreaks:
  • Active bird surveillance to detect the presence of WNV activity
  • Active mosquito surveillance to detect viral activity in mosquito populations
  • Passive surveillance by veterinarians and human health care professionals to detect neurologic illnesses consistent with encephalitis
• Personal precautions to avoid mosquito bites including use of repellents, protective clothing, screens, and installation of air conditioners
• Vaccines for prevention of most arbovirus infections are not available. A vaccine is available for Japanese encephalitis for travelers to endemic areas who are planning prolonged stays.
• Infection control measures:
  • Standard precautions are recommended for the hospitalized patient.
  • Respiratory precautions are recommended when vector mosquitoes are present.

West Nile Virus - epidemiology

• Arboviruses are spread by mosquitoes, ticks, and sand flies. The major vector for WNV in the United States is the Culex mosquito. WNV has been spread through blood transfusions and transplanted organs.
• Arboviruses are maintained in nature through cycles of transmission among birds, horses, and small animals. Humans and domestic animals are infected incidentally as “dead-end” hosts.
• Disease among birds has been a hallmark of WNV in the US and has served as a sensitive surveillance indicator of WNV activity.
• Each North American arbovirus has specific geographic distributions and is associated with a different ratio of asymptomatic-to-clinical infections. These agents cause disease of variable severity and have distinct age-dependent effects. WNV has now been identified throughout the US and is also found in Europe, Africa, and Asia.

West Nile Virus - incidence

• The peak incidence of arboviral encephalitis occurs during the late summer and early fall. Seasonality depends on the breeding and feeding seasons of the arthropod host.
• WNV is the leading cause of arboviral CNS disease. Encephalitis is most commonly seen in older adults, generally aged >50 years. Cases of WNV in children are unusual.
• A median of 3–5 cases of Western equine encephalitis and Eastern equine encephalitis are reported nationally each year. Eastern equine encephalitis tends to produce a more fulminant illness than LaCrosse or Western equine encephalitis.

West Nile Virus - pathophysiology

• The incubation period for WNV and other arboviral encephalitis agents is 5–21 days.
• The incubation period reflects the time necessary for viral replication, viremia, and subsequent invasion of the CNS.
• Virus replication begins locally at the site of the insect bite; transient viremia leads to spread of virus to liver, spleen, and lymph nodes. With continued viral replication and viremia, seeding of other organs including the CNS occurs.
• Virus can rarely be recovered from blood within the 1st week of onset of illness but not after neurologic symptoms have developed.

West Nile Virus - etiology

• Arboviruses can be divided into two groups based on the predominant clinical syndrome
• In the US, seven arboviruses are important causes of encephalitis: WNV, California encephalitis virus (LaCrosse strain), Eastern equine encephalitis, Western equine encephalitis, St. Louis encephalitis, Powassan encephalitis virus, and Venezuelan equine encephalitis virus.
• Arboviruses such as yellow fever, dengue fever, and Colorado tick fever typically cause acute febrile diseases and hemorrhagic fevers and are not characterized by encephalitis.
• Clinical manifestations of WNV:
  • Asymptomatic-most common
  • Self-limited febrile illness
  • Neuroinvasive disease-aseptic meningitis, encephalitis, or flaccid paralysis

West Nile Virus - DIAGNOSIS

West Nile Virus - signs & symptoms

West Nile Virus - history

• The diagnosis of arboviral infections of the CNS is difficult.
• Characteristic epidemiology that suggests a specific etiology is an important part of the history.
• The season of disease, prevalent diseases within the community, and animal exposures may provide clues to the diagnosis:
  • Enteroviral infections are seen in the warmer months (summer and early fall) in temperate climates.
  • Mosquito propagation in damp climates during the summer months may increase the likelihood of arthropod-borne viruses.
  • History of an animal bite or bat exposure may suggest the possibility of rabies.
• WNV (symptomatic infection) is characterized by sudden onset of fever, headache, myalgias, muscle weakness, and GI symptoms (nausea, vomiting, or diarrhea).
• Neuroinvasive WNV is characterized by neck stiffness and headache and/or mental status changes.

West Nile Virus - physical exam

• Encephalitis caused by arboviruses is characterized by acute onset of fever and headache in almost all patients. Associated symptoms include seizures, altered consciousness, disorientation, and behavioral disturbances. Neurologic signs are more commonly diffuse, but may be focal. These clinical findings can help to distinguish patients with meningitis, which is characterized by nuchal rigidity and fever usually without an altered sensorium.
• Another sign observed in WNV iinfection:
  • A rash is seen in ~50% of patients and is described as nonpruritic, roseolar, or maculopapular on the chest, back, and arms, which lasts 1 week.
  • Diffuse lymphadenopathy is also common.
• Neurologic examination in WNV infection reveals motor weakness or flaccid paralysis, increased deep tendon reflexes and extensor plantar responses, and tremor or abnormal movement of extremities

West Nile Virus - tests

The diagnosis of arboviral encephalitis depends on the recognition of epidemiologic risk factors and typical signs and symptoms with the aid of laboratory and radiographic studies.

West Nile Virus - lab

• Routine laboratory tests:
  • CBC typically reveals a mild leukocytosis.
  • Mild increase in ESR rate
  • Mild to moderate CSF pleocytosis predominately mononuclear cells
  • Elevated CSF protein
  • Normal CSF glucose
• Serology:
  • IgM and IgG ELISA for WNV and other arboviruses are performed at state public health laboratories and the CDC.
  • The diagnosis of arbovirus encephalitis is made by one of the following:
    • Detection of virus-specific IgM antibodies in the CSF is confirmatory.
    • A fourfold rise in serum antibody titers is confirmatory. Acute-phase titers should be collected 0–8 days after onset of symptoms. Convalescent phase titers should be collected 14–21 days after acute specimen. A single negative acute-phase specimen is inadequate for diagnosis, but a positive test can provide evidence of recent infection.
    • Isolation of the virus from tissue, blood, or CSF
    • Polymerase chain reaction (PCR) to detect viral RNA

West Nile Virus - imaging

• Imaging studies such as MRI or CT can assist in ruling out other potential causes of encephalopathy or encephalitis.
• MRI has proved useful in differentiating postinfectious encephalomyelitis from acute viral encephalitis. The former is characterized by enhancement of multifocal white matter lesions.

West Nile Virus - diag proced-surgery

EEG:

• Diffuse generalized slowing of brain waves
• Periodic high-voltage spike waves originating in the temporal lobe region and slow-wave complexes at 2–3-second intervals are suggestive of herpes simplex virus infection.

West Nile Virus - differencial diagnosis

Infectious:

• Viral:
  • Herpes simplex virus
  • Enteroviruses
  • HIV
  • HHV-6
  • Epstein-Barr virus
  • Cytomegalovirus
  • Lymphocytic choriomeningitis virus
  • Rabies
  • Mumps
  • Influenza
  • Adenovirus
• Nonviral:
  • Cat scratch disease (Bartonella henselae)
  • Mycoplasma pneumoniae
  • Postinfectious encephalomyelitis—generally follows a vague viral syndrome, usually upper respiratory tract, by days to weeks
  • Abscess/Subdural empyema
  • Meningitis:
    • Tuberculous
    • Cryptococcal or other fungal (histoplasmosis, coccidioidomycoses, blastomycoses)
    • Bacterial
    • Listeria
  • Toxoplasmosis
  • Plasmodiumfalciparum infection (malaria)
  • Parasites (cysticercosis, echinococcus, amebiasis, trypanosomiasis)

Noninfectious:

• Tumor
• Carcinomatous meningitis
• Systemic lupus erythematosus
• Sarcoidosis
• Vasculitis
• Hemorrhage
• Toxic encephalopathy
• Metabolic disorders

West Nile Virus - TREATMENT

West Nile Virus - general measures

• No specific antiviral therapy is available.
• Supportive therapy including cardiorespiratory function, fluid and electrolyte balance, seizure control, and reduction of intracranial pressure is important.
• Recovery can often be seen after prolonged periods of coma.

West Nile Virus - FOLLOW UP

West Nile Virus - prognosis

• Prognosis for recovery depends on the specific infecting agent and host factors such as age and underlying illness.
• Eastern equine encephalitis has the worst prognosis with mortality occurring in 30% of cases.

West Nile Virus - complications

• Optic neuritis
• Seizures
• Coma
• Death
• Guillain-Barré syndrome
• Severe neurologic sequelae
• Myocarditis
• Pancreatitis
• Hepatitis

West Nile Virus - patient monitoring

Neurobehavioral follow-up should be considered in children with severe or complicated disease.

West Nile Virus - bibliography

American Academy of Pediatrics. Arboviruses. In: Pickering LK, ed. 2006 Red Book: Report of the Committee on Infectious Diseases. 27th ed. Elk Grove Village, IL: American Academy of Pediatrics; 2003:211–217.American Academy of Pediatrics. West Nile Virus. In: Pickering LK, ed. 2006 Red Book: Report of the Committee on Infectious Diseases. 27th ed. Elk Grove Village, IL: American Academy of Pediatrics; 2003:729–732.
1. Asnis DS, Conetta R, Teixeira AA, et al. The West Nile virus outbreak of 1999 in New York: The Flushing Hospital experience. Clin Infect Dis. 2000;30:413–418.
2. CDC. Guidelines for surveillance, prevention and control of West Nile virus infection—United States. MMWR. 2003;52:1160.
3. Romero JR, Newland JG. Viral meningitis and encephalitis: Traditional and emerging viral agents. Semin Pediatr Infect Dis. 2003;14:72–82.

West Nile Virus - CODES

West Nile Virus - icd9

• 049.8 Viral
• 062.0–064 Encephalitis arthropod borne
• 062.2 Eastern equine
• 062.1 Western equine
• 062.5 La Crosse

West Nile Virus - FAQ

• Q: Should testing for arboviruses, including WNV, be performed on all patients with encephalitis?
• A: Diagnostic testing for arboviruses is not recommended for all patients with encephalitis. The prevalence of these diseases is low, and the diagnosis of more common causes of childhood encephalitis (e.g., herpes simplex virus) should be pursued initially. Patients with no other identifiable cause of encephalitis who have epidemiologic risk factors such as geographic location, season, and exposure history suggestive of arbovirus encephalitis should be evaluated. Testing of patients with aseptic meningitis or Guillain-Barré syndrome is low yield.

Book Source Details

• Book Title: The 5-Minute Pediatric Consult
• Author(s): M. William Schwartz MD; et al.
• Year of Publication: 2008
• Copyright Details: The 5-Minute Pediatric Consult, Copyright © 2008 Lippincott Williams & Wilkins.

More About West Nile fever

• Back to disease: West Nile fever: Introduction
• Next Book Extract About West Nile fever: Surveys relating to West Nile fever
• More Book Extracts: All Online Books for West Nile fever

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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.

More About This Book: Title: The 5-Minute Pediatric Consult Authors: M. William Schwartz MD; et al. Publisher: Lippincott Williams & Wilkins Copyright: 2008 ISBN: 0-7817-7577-9

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