West Nile virus: Difference between revisions

Revision as of 09:41, 29 August 2023

Background

Virology

Single-stranded positive-sense enveloped virus in the family Flaviviridae and genus Flavivirus, within the Japanese encephalitis serocomplex
Five lineages, of which only lineage 1 and 2 cause outbreaks in humans

Epidemiology

Essentially worldwide distribution
Vector is mosquitoes, particularly Culex mosquitoes
Main reservoir is birds, particularly crows, jays, magpies, and ravens; also horses
- Humans are an incidental host and not generally involved in transmission
Disease in humans is seasonal, with most cases July through September
As well as being vector-borne, can also be transmitted by blood transfusion, solid organ transplantation, and vertically

Clinical Manifestations

Incubation period of 3 to 14 days, with range of 2 to 21 days
Up to 80% of infections are asymptomatic
Of the 20% with symptoms, fever is most common
- Other common symptoms include headaches, generalized weakness, morbilliform or maculopapular rash (often occuring at defervescence), and myalgias
- Less common symptoms include arthralgias, chills, eye pain, vomiting, diarrhea, and lymphadenopathy
- Generally self-resolves within days to weeks with complete recovery, though fatigue may linger

West Nile Neuroinvasive Disease

Some form of CNS disease develops in 1:150 people
Meningoencephalitis
- Meningitis with usual presentation (nuchal rigidity, headache, photophobia, phonophobia, fever)
- Encephalitis with altered level of consciousness, lethargy, personality changes
Acute flaccid paralysis with acute onset and rapidly-progressive limb weakness
- Usually asymmetry, areflexic/hyporeflexic, with preserved sensation
- Usually but not always in the context of meningoencephalitis
Also may have nausea/vomiting, myalgias, arthralgias, chills, rash, ataxia, visual disturbance, tremors, myoclonus, bulbar dysfunction
Usually self-resolves over weeks to months, but half have neuropsychiatric sequelae (including function/cognitive dysfunction and paralysis)
- 10% mortality

Differential Diagnosis

Other causes of meningitis, encephalitis, and acute flaccid paralysis

Diagnosis

Serology
- Serum or CSF for IgM antibodies is the standard test; usually positive by 3 to 8 days, and persist for 2 to 3 months
  - If submitted CSF, must also submit serum
- May cross-react with other flaviviruses
- Can be seronegative if immunosuppressed (e.g. rituximab), therefore may need to do PCR
PCR
- RNA virus, therefore needs reverse transcriptase step (RT-PCR)
- Can be done on serum, CSF, and tissue
On MRI, may have a slight preference for thalamus

Management

Supportive care

@@ Line 1: / Line 1: @@
 == Background ==
+=== Virology ===
-* Single-stranded positive-sense enveloped virus in the family [[Flaviviridae]] and genus [[Flavivirus]]
+* Single-stranded positive-sense enveloped virus in the family [[Family::Flaviviridae]] and genus [[Genus::Flavivirus]], within the Japanese encephalitis serocomplex
+* Five lineages, of which only lineage 1 and 2 cause outbreaks in humans
+=== Epidemiology ===
 * Essentially worldwide distribution
-* Vector is [[Vector::mosquitoes]]
+* Vector is [[Vector::mosquitoes]], particularly [[Culex]] mosquitoes
-* Main reservoir is birds
+* Main reservoir is birds, particularly crows, jays, magpies, and ravens; also horses
+** Humans are an incidental host and not generally involved in transmission
+* Disease in humans is seasonal, with most cases July through September
 * As well as being vector-borne, can also be transmitted by blood transfusion, solid organ transplantation, and vertically
 == Clinical Manifestations ==
-* Incubation period of [[Usual incubation period::3 to 14 days]]
+* Incubation period of [[Usual incubation period::3 to 14 days]], with range of [[Incubation period range::2 to 21 days]]
-* Up to 80% of infections are asymptomatic; of those with symptoms, [[fever]] is most common
+* Up to 80% of infections are asymptomatic
+* Of the 20% with symptoms, [[fever]] is most common
+** Other common symptoms include headaches, generalized weakness, morbilliform or maculopapular rash (often occuring at defervescence), and myalgias
+** Less common symptoms include arthralgias, chills, eye pain, vomiting, diarrhea, and lymphadenopathy
+** Generally self-resolves within days to weeks with complete recovery, though fatigue may linger
+=== West Nile Neuroinvasive Disease ===
 * Some form of CNS disease develops in 1:150 people
-** [[Meningoencephalitis]]
+* [[Meningoencephalitis]]
+** [[Meningitis]] with usual presentation (nuchal rigidity, headache, photophobia, phonophobia, fever)
-** [[Acute flaccid paralysis]]
+** [[Encephalitis]] with altered level of consciousness, lethargy, personality changes
-** 10% mortality, with about half of survivors having neuropsychiatric sequelae
+* [[Acute flaccid paralysis]] with acute onset and rapidly-progressive limb weakness
+** Usually asymmetry, areflexic/hyporeflexic, with preserved sensation
+** Usually but not always in the context of meningoencephalitis
+* Also may have nausea/vomiting, myalgias, arthralgias, chills, rash, ataxia, visual disturbance, tremors, myoclonus, bulbar dysfunction
+* Usually self-resolves over weeks to months, but half have neuropsychiatric sequelae (including function/cognitive dysfunction and paralysis)
+** 10% mortality
 == Differential Diagnosis ==
@@ Line 35: / Line 53: @@
 * Supportive care
+== Further Reading ==
+* West Nile Virus: Review of the Literature. ''JAMA.'' 2013;310(3):308–315. doi:[https://doi.org/10.1001/jama.2013.8042 10.1001/jama.2013.8042]
 [[Category:Flaviviridae]]