Doctor123.org

West Nile Virus, Emergency Medicine

Basics

Description

- Neurologic: - Altered mental status (change in level of consciousness, confusion, agitation, irritability) - Severe, diffuse muscle weakness; may be asymmetric and involve the face - Flaccid paralysis, which may resemble poliomyelitis-like syndrome, associated with anterior horn cell injury. Cranial nerve and bulbar abnormalities have been reported - May resemble Guillain " “Barre syndrome - Seizures - Encephalitis more commonly reported in adults and meningitis in children

- GI: - Nausea, vomiting, diarrhea, anorexia - Abdominal pain

- Musculoskeletal: - Myalgia - Arthralgia - Back pain

- Cardiovascular: - Ophthalmologic: - Optic neuritis - Vitritis - Chorioretinitis

- CSF: - Pleocytosis with lymphocyte predominance - Elevated protein - Normal glucose

- Other causes of meningitis: - Bacterial - Viral - Tuberculous - Fungal

- Other causes of viral encephalitis: - Other arboviruses, especially St. Louis encephalitis virus - Enterovirus, particularly in patients ≤16 yr of age - Herpes simplex virus (HSV) - Cytomegalovirus (CMV) - Epstein " “Barr virus (EBV) - Mumps virus - Varicella zoster virus - Rabies virus

Infectious agent is an arbovirus, an RNA member of the Flaviviridae family. ‚

Etiology

  • Vector-borne virus
  • Transmitted by infected mosquitoes in late summer/early fall
  • Wild birds are primary reservoir hosts; humans are infected by cross-feeding mosquitoes.
  • Introduced to Western Hemisphere in 1999; became more widespread owing to vector of Culex mosquito and is now endemic in North America
  • Infection after blood transfusion and solid-organ transplant can occur.
  • There are case reports of occupational exposure and infection of lab workers via percutaneous inoculation.
  • Following recovery, immunity is considered lifelong. Reoccurrence is rare
  • The 2011 outbreak had a mortality rate of 4 " “5%. Cases were reported in 48 states.

Infection via transplacental transmission and breast-feeding has been reported. ‚

Diagnosis

Signs and Symptoms

  • Variable severity of illness:80% asymptomatic20% mild symptoms, flu-like illness ¢ ˆ ¼1/150 with CNS involvement (encephalitis, meningitis)
  • Incubation period is usually 2 " “6 days but can be up to 14 days in average patient and up to 21 days in immunocompromised patient.
  • Symptoms have a sudden onset and last <1 wk with mild infection.
  • Mortality rate in severe cases is estimated at 7%.
  • Severity of illness is related to degree of CNS invasion by virus. Risk is enhanced with increased age and immunosuppression
  • Immunocompromised patients have prolonged viremia, delayed development of antibody, and increased likelihood of severe disease.
  • Persistent symptoms of fatigue, memory impairment, weakness, and headache have been reported to last for 1 " “2 mo
  • Patients >60 yr, if infected, are at higher risk for developing more severe disease and neurologic consequences.
  • Advanced age is the most important risk factor for death.

History

  • General:FeverMalaiseAnorexiaHeadacheAcute phase resolves within several days but fatigue and weakness may persist for weeks
  • Neurologic:Altered mental status (change in level of consciousness, confusion, agitation, irritability)Severe, diffuse muscle weakness; may be asymmetric and involve the faceFlaccid paralysis, which may resemble poliomyelitis-like syndrome, associated with anterior horn cell injury. Cranial nerve and bulbar abnormalities have been reportedMay resemble Guillain " “Barre syndromeSeizuresEncephalitis more commonly reported in adults and meningitis in children
  • GI:Nausea, vomiting, diarrhea, anorexiaAbdominal pain
  • Musculoskeletal:MyalgiaArthralgiaBack pain
  • Respiratory:
  • Ophthalmologic:

Physical Exam

  • General:Temperature >38 ‚ °C (>100 ‚ °F)Transient maculopapular rashRhabdomyolysis
  • Neurologic:Altered mental statusHyporeflexia, areflexiaAtaxiaExtrapyramidal signsCranial nerve palsies, paresisMyoclonusProfound motor weaknessFlaccid paralysis
  • GI:Hepatosplenomegaly, hepatitis, pancreatitis
  • Musculoskeletal:
  • Hematologic:
  • Dermatologic:Rash (maculopapular or morbilliform on neck, trunk, extremities) usually lasting <1 wk
  • Cardiovascular:
  • Ophthalmologic:Optic neuritisVitritisChorioretinitis

Essential Workup

  • Most sensitive screening test is serologic testing of CSF and serum for IgM antibody-capture enzyme-linked immunosorbent assay (MAC-ELISA) and culture.
  • Centers for Disease Control and Prevention (970-221-6400)
  • Can be detected during 1st 4 days of illness, nearly all tests are positive by day 7 " “8; may remain positive up to 1 yr after infection
  • Procedures for submitting samples vary by state.
  • Refer to local public health department for guidelines.

Diagnosis Tests & Interpretation

Lab

  • CSF:Pleocytosis with lymphocyte predominanceElevated proteinNormal glucose
  • CBC:WBCs may be mildly elevated (50%) or normal.Leukopenia may be present (15%).Anemia can occur.
  • Chemistry:Hyponatremia sometimes seen:Cause uncertain, possibly syndrome of inappropriate antidiuretic hormone (SIADH) when CNS involvement existsPancreatitis (rare)Fulminant hepatitis (rare)

Imaging

  • CT head usually normal
  • MRI can be useful to identify CNS inflammation:1/3 of patients show abnormality.Imaging findings generally nonspecific but may include enhancement of leptomeninges and/or periventricular white matter or can mimic demyelinating process.

Diagnostic Procedures/Surgery

  • Lumbar puncture
  • MAC-ELISA may be used on serum and CSF samples

Differential Diagnosis

  • Other causes of meningitis:BacterialViralTuberculousFungal
  • Other causes of viral encephalitis:Other arboviruses, especially St. Louis encephalitis virusEnterovirus, particularly in patients ≤16 yr of ageHerpes simplex virus (HSV)Cytomegalovirus (CMV)Epstein " “Barr virus (EBV)Mumps virusVaricella zoster virusRabies virus
  • Intracranial abscess
  • CNS vasculitis
  • Nonspecific viral syndrome
  • Gastroenteritis

Treatment

Initial Stabilization/Therapy

Ed Treatment/Procedures

  • Supportive care
  • IV fluids for signs of dehydration
  • For signs of meningitis, administer antibiotics pending results of CSF.
  • Consider acyclovir if index of suspicion for the only treatable cause of viral encephalitis, HSV, is high.
  • Administer antipyretics and pain medications.
  • No known effective antiviral therapy or vaccine
  • No controlled studies proving effectiveness of interferonα-2b, ribavirin, corticosteroids, anticonvulsants, or osmotic agents

Follow-Up

Disposition

Admission Criteria

  • Neurologic symptoms
  • Dehydration
  • Concerning risk factors (advanced age, immunocompromise)

Discharge Criteria

  • No signs of CNS involvement (encephalitis, meningitis)
  • Able to tolerate oral solutions

Followup Recommendations

Neurologist to monitor for potential ongoing residual. ‚

Pearls and Pitfalls

Consider HSV in differential, since HSV is treatable. ‚

Additional Reading

  • Centers for Disease Control and Prevention (CDC): Interim guidelines for the evaluation of infants born to mothers infected with West Nile Virus during pregnancy. MMWR Morb Mortal Wkly Rep. 2004;53:154 " “157.
  • Hayes ‚ EB, O 'Leary ‚ DR. West Nile virus infection: A pediatric perspective. Pediatrics. 2004;113:1375 " “1381.
  • Loeb ‚ M, Hanna ‚ S, Nicolle ‚ L, et al. Prognosis after West Nile virus infection. Ann Intern Med. 2008;149:232 " “241.
  • Petersen ‚ LR, Marfin ‚ AA, Gubler ‚ DJ. West Nile virus. JAMA. 2003;290:524 " “528.
  • Peterson ‚ LR, Hayes ‚ EB: West Nile virus in the Americas. Med Clin North Am. 2008;92:1307 " “1322.
  • West Nile Virus: Information and Guidance for Clinicians. Available at http://www.cdc.gov/ncidod/dvbid/westnile/clinicians
  • Zak ‚ IT, Altinok ‚ D, Merline ‚ JR, et al. West Nile virus infection. AJR Am J Roentgenol. 2005;184(3):957 " “961.

See Also (Topic, Algorithm, Electronic Media Element)

Meningitis; Encephalitis, HSV ‚

Codes

ICD9

  • 066.40 West Nile Fever, unspecified
  • 066.41 West Nile Fever with encephalitis
  • 066.42 West Nile Fever with other neurologic manifestation
  • 066.49 West Nile Fever with other complications
  • 066.4 West nile fever

ICD10

  • A92.30 West Nile virus infection, unspecified
  • A92.31 West Nile virus infection with encephalitis
  • A92.32 West Nile virus infection with oth neurologic manifestation
  • A92.39 West Nile virus infection with other complications
  • A92.3 West Nile virus infection

SNOMED

  • 417093003 Disease due to West Nile virus (disorder)
  • 392662004 West Nile encephalitis (disorder)
  • 430397002 disorder of nervous system due to West Nile virus (disorder)
  • 404233006 West Nile meningitis (disorder)
  • 397420007 West Nile fever without encephalitis (disorder)