19.2 Flashcards
arbovirus encephalitis is most commonly caused by
flaviviruses
most important flaviviruses causing encephalitis are
japanese encephalitis virus
murray valley encephalitis vrus
west nile virus
murray valley encephalits virus is closely related to
japanese encephalitis virus
infection with murray valley encephalitis vrus
most ifections are asymptomatic - only a small proportin develop encephalitis
japanese encephalitis transmitted by
mosquitos - culex and aedes
mnatural cycel of tranmsision primarly involves pigs, also birds, bats, reptiles
man is not preferred host, transmission to hu,ans usually only occurs when mosquito populations are large
japanese encephalitis distribution
asia, south east asia, india subcontinent
has been detected on torres strait island, north queensland
manly a disease of rural areas
japanese encephalitis prevention
vaccine available
japanese encephalitis clinical signs
> 99% infections are subclinical
in areas of endemic transmission >80% adults are immune
mainly a disease affecting children 2-10 years, can also affect the elderly
occasionally seen in returned travellers
encephalitis usually severe
may present with high fever, altered consciousness, mild disorientation to severe confusion, delirium or coma
cranial nerve palsies are common
incubation period of japanese encephalitis
4-21 days
sequelae of JE
multiple seizures and status elipticus associated with poor outcome
long term neurological sequelae are common
JE MRI appearance
often diffuse white matter oedema, abnormal signals in thalamus, basal ganglia, cerebellum, midbrain, spinal cord
murray valley encephalitis
endemic in australia, top end and northern WA
- mosquito vector, Culex sp.
belongs to the JE complex of flvaivirus along with JE, WNV, and Kunjin virus
natural cycle involves mosquitos and waterbirds
vector of murray vellay encephalitis
culex sp.
monitoring of murray valley encephalitis
sentinel chickens
used to monitor flavivirus activity in an area
incubation period of murray valley encephalitis
1-4 weeks
clincial symptoms of murray valley encephalitis
can affect patients of any age broud spectrum of disease prodrome of 2-5 days fever and headache initial neurological features can include lethargy, irritability, confusion siezures common in children
4 main patterns of progression of murray valley encaphlaitis
- progression to death
- spinal cord involvement and flaccid paralysis
- cranial nerve and brainstem involvement with tremor
- encephalitis and complete recovery
MRI changes in murray valley encephalitis
may be visible within a week of symptom onset
changes include
- hyperintensity of deep grey matter, especially thalamus
- changes may also involve temporal lobe and cervical spinal cord
west nile virus distribution
most common cause of epidemic encephalitis in US
epidemic and endemic transmission in africa, asia, mediterranean
related to kunjin virus - found in australia
west nile virus vetor
culex sp.
natural cycle between mosquitos and birds
west nile virus incubation period
2-14 day
symptoms of west nile virus
80% infectious symptomatic
approx 20% develop acute, febrile, flu-like illness
<1% develop maningitis or encephalitis
neuroinvasive disease more common in patients >60 years
febrile prodrome
severe acute flaccid paralysis may occur, can resemble polio
MRI changes in west nile virus
can appear normal in 30-50%
changes usually involve the thaalamus, basal gnaglia and brainstem
sequelea of west nile virus
mortality fo around 12% in neuro-nvasive disease
long term neurological sequelae are common
laboratory diagnosis of arbovirus encephalitis
CSF
serology on CSF
serology
PCR
CSF for abrovirus encephalitis
elevated white cell count with lymphocytic pleocytosis
WCC may be normal, particularly when collected early in disease
glucose typically normal, protein typically raised
serology on CSF for arbovirus diagnosis
detection of specific IgM
serology for arbovirus diagnosis
patient serum for IgM and IgG
demonstration seroconversion
PCR arbovirus encephalitis
plasma and CSF
negative result does not exclude flavivirus encephalitis
are flavivirus infections notifiable
yes
