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 | *RNA virus | ||
*Virus family | *Virus family associated with St Louise encephalitis, Japanese encephalitis, Murray Vallen enceph, and Kunjin enceph | ||
*2 lineage of WNV - only lineage 1 | *2 lineage of WNV - only lineage 1 associated with human disease originating in Middle East/Israel | ||
===Ecology=== | ===Ecology=== | ||
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*Starts in spring, ends in fall when mosquitos dormant | *Starts in spring, ends in fall when mosquitos dormant | ||
*Culex mosquitos | *Culex mosquitos | ||
*Unclear if human infection from culex bite or other bridge vector | *Unclear if human infection from culex bite or other bridge vector mosquito species | ||
*House sparrows have high level of viremia and are amplifiers | *House sparrows have high level of viremia and are amplifiers | ||
*Humans and horses also but viremia is low so are not important amplifiers | *Humans and horses also but viremia is low so are not important amplifiers | ||
*WNV in birds feces and oral secretions | *WNV in birds feces and oral secretions | ||
*Bird to bird | *Bird to bird transmission possible in lab | ||
*Birds can be infected by eating | *Birds can be infected by eating infected mosquitoes, birds or odents but importance of oral spread in nature unclear | ||
===Epidemiology=== | ===Epidemiology=== | ||
*Found in Africa, | [[File: Global_distribution_of_West_Nile_virus-CDC.gif|thumb|Global Distribution of West Nile Virus. Source: CDC]] | ||
*Most human | *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 | *Human Transmission | ||
**Most from | **Most from mosquito bites | ||
**Maternal fetal | **Maternal fetal | ||
**Breast milk | **Breast milk | ||
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*2-14 day incubation | *2-14 day incubation | ||
*Illness for 3-6 days | *Illness for 3-6 days | ||
*Malaise, anorexia, | *Malaise, anorexia, nausea/[[vomiting]], [[eye pain]], [[headache]], [[myalgia]], [[rash]] | ||
*20% of | *20% of infected patients get West Nile fever | ||
*<1% get severe neuro problem- encephalitis, meningitis, acute flaccid paralysis | *<1% get severe neuro problem- [[encephalitis]], [[meningitis]], acute flaccid [[weakness|paralysis]] | ||
*Can also get movement disorder- tremor, myoclonus, Parkinsonism, bradykinesia | *Can also get movement disorder- [[tremor]], myoclonus, Parkinsonism, bradykinesia | ||
*Can also have cranial nerve, optic neuritis, | *Can also have [[cranial nerve palsies|cranial nerve involvement]], [[optic neuritis]], [[seizure]] | ||
*Myocarditis, pancreatitis, fulminant hepatitis | *[[Myocarditis]], [[pancreatitis]], fulminant hepatitis | ||
*Acute flaccid paralysis | *Acute flaccid [[paralysis]] | ||
**Weakness can affect upper or lower limbs and can happen without meningitis | **Weakness can affect upper or lower limbs and can happen without meningitis | ||
**Can become hypo/areflexic, acute bowel and bladder | **Can become hypo/areflexic, acute bowel and bladder dysfunction, absence of pain, or sensory changes | ||
**CSF has increased protein and pleocytosis | **[[LP|CSF]] has increased protein and pleocytosis | ||
**Similar polio with destruction of spinal anterior horn cells as | **Similar to [[polio]] with destruction of spinal anterior horn cells as opposed to GBS | ||
==Differential Diagnosis== | ==Differential Diagnosis== | ||
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*[[SAH]] | *[[SAH]] | ||
*[[Lyme disease]] | *[[Lyme disease]] | ||
*Brain abscess | *[[Brain abscess]] | ||
*Bacterial [[endocarditis]] | *Bacterial [[endocarditis]] | ||
*Toxic / metabolic encephalopathy | *Toxic / metabolic encephalopathy | ||
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{{AMS and fever DDX}} | {{AMS and fever DDX}} | ||
== | ==Evaluation== | ||
* | *WBC count normal or slightly elevated | ||
*CSF - pleocytosis with lymphocyte predominance and elevated protein | *[[LP|CSF]] - pleocytosis with lymphocyte predominance and elevated protein | ||
*CT head | *[[CT head]]- negative | ||
*MRI brain usually | *[[brain MRI|MRI brain]] usually negative but can show focal lesion in pons, basal gang, thal | ||
*Confirmation by blood or CSF IgM | *Confirmation by blood or [[LP|CSF]] IgM | ||
**IgM does not cross BBB so CSF IgM indicated CNS infc | **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 | *False positive is recently vaccinated for yellow fever, Jap enceph, or recently infected with relate flavivirus- St Louse, Dengue | ||
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*4- 18% fatality | *4- 18% fatality | ||
*Older age greatest risk for death | *Older age greatest risk for death | ||
*Risk for poor neuro outcome and death- encephalitis, severe muscle weakness, | *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 | *Can have significant morbidity and loss of function even in those patients that survive and are discharged to home | ||
*Parkinsons, tremor, gait, balance | *[[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 | *Initial severe encephalopathy did not mean poor neuro outcome | ||
*Acute flaccid paralysis typically has very poor recovery | *Acute flaccid paralysis typically has very poor recovery | ||
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==Disposition== | ==Disposition== | ||
Admit | Admit | ||
==External Links== | |||
https://www.cdc.gov/westnile/index.html | |||
==See Also== | ==See Also== | ||
*[[Encephalitis]] | *[[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.