West Nile virus
Background
Virolgy
- RNA virus
- Virus family associated with St Louise encephalitis, Japanese encephalitis, Murray Vallen enceph, and Kunjin enceph
- 2 lineage of WNV - only lineage 1 associated with human disease originating in Middle East/Israel
Ecology
- Bird- mosquito- bird cycle
- Passerine birds are amplification host
- Starts in spring, ends in fall when mosquitos dormant
- Culex mosquitos
- Unclear if human infection from culex bite or other bridge vector mosquito species
- House sparrows have high level of viremia and are amplifiers
- Humans and horses also but viremia is low so are not important amplifiers
- WNV in birds feces and oral secretions
- Bird to bird transmission possible in lab
- Birds can be infected by eating infected mosquitoes, birds or odents but importance of oral spread in nature unclear
Epidemiology
- Found in Africa, Middle East, Russia, Australia
- First appeared in eastern US in 1999 but now found nationwide[1]
- Most human infections occur in August and Sept but can happen from May to Dec
- Human Transmission
- Most from mosquito bites
- Maternal fetal
- Breast milk
- Blood transfusion
- Percutaneous lab infection
Clinical Features
- Most people asymptomatic
- Severity increases with age
- 2-14 day incubation
- Illness for 3-6 days
- Malaise, anorexia, nausea/vomiting, eye pain, headache, myalgia, rash
- 20% of infected patients get West Nile fever
- <1% get severe neuro problem- encephalitis, meningitis, acute flaccid paralysis
- Can also get movement disorder- tremor, myoclonus, Parkinsonism, bradykinesia
- Can also have cranial nerve involvement, optic neuritis, seizure
- Myocarditis, pancreatitis, fulminant hepatitis
- Acute flaccid paralysis
Differential Diagnosis
- Meningitis
- SAH
- Lyme disease
- Brain abscess
- Bacterial endocarditis
- Toxic / metabolic encephalopathy
Altered mental status and fever
- Infectious
- Sepsis
- Meningitis
- Encephalitis
- Cerebral malaria
- Brain abscess
- Other
Evaluation
- WBC count normal or slightly elevated
- CSF - pleocytosis with lymphocyte predominance and elevated protein
- CT head- negative
- MRI brain usually negative but can show focal lesion in pons, basal gang, thal
- Confirmation by blood or CSF IgM
- IgM does not cross BBB so CSF IgM indicated CNS infc
- False positive is recently vaccinated for yellow fever, Jap enceph, or recently infected with relate flavivirus- St Louse, Dengue
- Confirmation by 4X increase of acute/ conv titres of antibodies
Management
- Supportive
- No studies to support ribavirin, interferon, gamma globulin, steroids, anticonvulsants, or osmotic agents
Prognosis
- 4- 18% fatality
- Older age greatest risk for death
- Risk for poor neuro outcome and death- encephalitis, severe muscle weakness, AMS, DM, immune suppression
- Can have significant morbidity and loss of function even in those patients that survive and are discharged to home
- Parkinsons, tremor, gait instability, balance problems are most common neuro findings after discharge to home
- Initial severe encephalopathy did not mean poor neuro outcome
- Acute flaccid paralysis typically has very poor recovery
Disposition
Admit
External Links
https://www.cdc.gov/westnile/index.html
See Also
References
- ↑ West Nile virus. Centers for Disease Control and Prevention website. Accessed January 15, 2021.