Viral Encephalitis Flashcards
Define encephalitis
Encephalitis – inflammation in the brain + neurological dysfunction
Viruses that cause encephalitis are ___
Viruses that cause encephalitis are neurotropic, meaning that are able to infect neural cells
Contrast neuroinvasiveness and neurovirulence
What is an example of a virus with low NI but high NV?
Neuroinvasiveness - ability to cross the BBB and enter the CNS
vs
Neurovirulence - ability to cause disease once in the CNS
HSV: low neuroinvasiveness but high neurovirulence (even if a little bit of it can get into the CNS, it’ll cause damage pretty much)
Two general methods of diagnosing encephalitis are ___
CSF evaluation via lumbar puncture
Brain imaging (MRI or CT +/- EEG)
What is the hallmark of encephalitis?
Altered mental status
**note: can present typically with non specific acute fever, headache, and focal neurological issues like seizures, weakness, speech disturbances**
What are the expected lab findings for viral encephalitis? (i.e. white count and glucose levels)
CSF: high WBC count, early PMNs, normal glucose
(vs meningitis where white count is much higher and glucose is lower)
What are the expected brain imaging findings for viral encephalitis? (abnormal/normal)
Neuroimaging is typically abnormal but there’s generally no typical pattern for individual infections
In general, Dx of viral encephalitis includes what 4 criteria?
Non specific: clinical findings, CSF eval, imaging
Specific: usually serology (IgM in peripheral blood), PCR tends not to work well b/c not enough virus to amplify and work with
With the exception of Herpes, most of the Rx of arbovirus is __
With the exception of Herpes, most of the Rx of arbovirus is supportive
What are the flavi viruses discussed?
West Nile virus
St Louis encephalitis virus
What are the Bunya virus members that cause encephalitis?
La Crosse (for this lecture but there’s also hanta virus)
Rhabdovirus members that cause encephalitis include __
Rabies virus
Togavirus members that cause encephalitis include ___ and ___
Eastern & Western Equine Encephalitis viruses
Describe the structure of WNV (envelope or no, shape of virion etc)
What type of sense/genome virus is it?
West Nile Virus:
Flavivirus
Enveloped icosahedral capsid
(+) sense single stranded RNA
Describe the transmission cycle of West Nile Virus
vector - culex mosquito
amplifier - birds (Passerine type, like crows and blue jays)
humans and horses - dead end hosts
**see below for cycle**
West Nile Virus replicates in ___ cells
Describe the viral replication cycle in these cells. Where does the virus go following replication?
West Nile Virus replicates in skin dendritic cells
Replication cycle (see image below):
viral attachment >> receptor-mediated endocytosis >> fusion >> uncoating >> translation etc >> making -ve ssRNA intermediate >> making more +ve ssRNA >> virion assembly >> furin cleavage
Virus replicates then goes into the lymphatics, then the blood stream, then the CNS
Describe the characteristics of EEEV and WEEV
Togavirus/alphavirus
Have enveloped icosahedral capsid and (+) ssRNA genome
**replication cycle is pretty much the same as that of WNV**
___ is a -ve sense segmented ssRNA Bunyavirus with an enveloped helical capsid that causes encephalitis
La Crosse virus
What is Powassan virus?
Flavivirus transmitted by ticks (Ixodes scapularis, Ixodes cookei)
*see below for everything else*
___ is a -ve sense ssRNA , enveloped helical capsid virus in the Rhabdovirus family
Rabies
**note that it makes the proteins below:
Glycoprotein
Matrix protein
Nucleoprotein
Phosphoprotein
L-polymerase
Describe the rabies replication cycle
- G protein attaches to receptors on nerve and muscle cells
- Entry via endocytosis
- Membrane fusion with lysosome, release of nucleocapsid into cytoplasm
- Transcription of mRNA, translation of 5 structural peptides
- Accumulation of N alters N:RNA ratio, switch to replication of genome
- Coating of (-) strand with N,L, and P to form nucleocapsid
- Coating with M, G added as virus is processed through golgi apparatus
- Budding
Describe the pathogenesis of rabies
Enters ms cells and replicates very slowly
Motor nerves >> retrograde axonal transport >> CNS >> variable neuronal necrosis etc >> dissemination
Incubation time: long
Has eosinophilic inclusion bodies called negri bodies
How do you Dx/Rx rabies infection?
Dx:
CSF or saliva PCR
DFA staining of skin biopsy in the nape of the neck
Rx: none once neuro sysmptoms start
What is the post exposure prophylaxis protocol for rabies and who would you give it to?
PEP:
IG given at site of infection; vaccine @ diff site
Who: (see slide below)
