West Nile virus: Difference between revisions
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==Background== | ==Background== | ||
===Virolgy=== | ===Virolgy=== | ||
[[File:Westnile.jpg|thumb|Micrograph of west nile virus. Source: https://pixnio.com/science/microscopy-images/west-nile-disease/micrograph-of-the-west-nile-virus]] | |||
*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=== | ===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=== | ===Epidemiology=== | ||
[[File: Global_distribution_of_West_Nile_virus-CDC.gif|thumb|Global Distribution of West Nile Virus. Source: CDC]] | |||
*Found in Africa, Middle East, Russia, Australia | |||
*First appeared in eastern US in 1999 but now found nationwide<ref>West Nile virus. Centers for Disease Control and Prevention website. Accessed January 15, 2021.</ref> | |||
*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 [[weakness|paralysis]] | |||
*Can also get movement disorder- [[tremor]], myoclonus, Parkinsonism, bradykinesia | |||
*Can also have [[cranial nerve palsies|cranial nerve involvement]], [[optic neuritis]], [[seizure]] | |||
*[[Myocarditis]], [[pancreatitis]], fulminant hepatitis | |||
*Acute flaccid [[paralysis]] | |||
**Weakness can affect upper or lower limbs and can happen without meningitis | |||
**Can become hypo/areflexic, acute bowel and bladder dysfunction, absence of pain, or sensory changes | |||
**[[LP|CSF]] has increased protein and pleocytosis | |||
**Similar to [[polio]] with destruction of spinal anterior horn cells as opposed to GBS | |||
==Diagnosis== | ==Differential Diagnosis== | ||
*[[Meningitis]] | |||
*[[SAH]] | |||
*[[Lyme disease]] | |||
*[[Brain abscess]] | |||
*Bacterial [[endocarditis]] | |||
*Toxic / metabolic encephalopathy | |||
{{AMS and fever DDX}} | |||
== | ==Evaluation== | ||
*WBC count normal or slightly elevated | |||
*[[LP|CSF]] - pleocytosis with lymphocyte predominance and elevated protein | |||
*[[CT head]]- negative | |||
*[[brain MRI|MRI brain]] usually negative but can show focal lesion in pons, basal gang, thal | |||
*Confirmation by blood or [[LP|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 | |||
*[[parkinson's disease|Parkinsons]], [[tremor]], [[ataxia|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== | |||
*[[Encephalitis]] | |||
==References== | |||
[[Category:ID]] | [[Category:ID]] | ||
[[Category:Neurology]] |
Latest revision as of 08:06, 15 January 2021
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.