Viral Encephalitis Flashcards
What is on your differential for fever/HA/confusion?
Works for any pathological process
Vitamin D
Vascular/ischemic
Infectious
Trauma
Autoimmune/inflammatory
Metabolic/systemic
Inherited/congenital
Neoplasm
Drug/toxic
What is the difference between viral meningitis and viral encephalitis?
Viral meningitis: viral infection of subarachnoid space
Symptoms = fever, HA, n/v, malaise, stiff neck, photophobia
Self-limited illness
Causes = enteroviruses, arboviruses, herpesviruses, acute HIV infecition, mumps
Viral encephalitis: viral infection of brain parenchyma
Symptoms = fever, HA, altered mental status, decreased consciousness, focal neurological findings
Causes = HSV-1, Arboviruses, enteroviruses
How do you distinguish the cause of meningitis?
CSF findings:
Bacterial = high protein (>100), low glucose (<40), neutrophilic pleocytosis
Viral = normal glucose, slightly elevated proteins, lymphocytic pleocytosis
Harder to distinguish viral/TB/cryptococcal meningitis
What is meninvoencephalitis?
When meningitis and encephalitis occur simultaneously
What is myelitis?
Inflammation of the spinal cord
Polio can cause poliomyelitis
West Nile Virus can also cause myelitis
Who is susceptible to viral encephalitis?
Very young, very elderly, immunocompromised
What viruses are more common in the summer?
Arboviruses, bc mosquito vector
How do neurotropic viruses enter the body/spread to nervous system?
- Enter host (respiratory trat, GI, GU, skin/subcutaneous tissue, ocular conjunctiva, direct inoculation to blood, transplant)
- Then adhere to M cells & transport to undelrying lymphoid tissue
- Hematogenous spread through BBB (where tight junctions aren’t so tight i.e. chorid plexus or through diapedesis
OR
- Neural spread i.e. Herpes 1/2, rabies, polio: retrograde transport
How do viruses cause neurovirulence?
Mostly direct effect of viral DNA: on cellular functions, cell death via apoptosis or necrosis
Some (JC virus) can infect oligodendroglial cells –> demyelination –> progressive multifocal leukoencephalopathy (PML)
Pathology is alsu due to host response to infection
How do you diagnose viral encephalitis?
Complete history including travel/exposures/sex/ immunization status
Signs: rash, lymphadenopathy, stiff neck,
Lab: PCR, serology, culture
- CSF profile: normal glucose, slightly elevated protein
- Rule out other causes: bacterial, fungal, parasitic, syphilis
Neuroimaging- MRI
How do you treat viral encephalitis?
Supportive care only
EXCEPT for HSV – treat with acycolvir
What features are indicative of HSV-1 viral encephalitis?
Reactivation from latency
Personality changes/bizarre behavior
Temporal lobe involvement: edema, enhancement, hemorrhage, mass effect
Hemorrhagic: find RBC in CSF
What strain of herpes virus is responsible for most herpes viral encephalitis?
HSV-1, 96%
What is the treatment for HSV-1 viral encephalitis?
Acyclovir- IV
Treat asap!! Even before you confirm diagnosis
What are common examples of arboviruses?
Togaviridae:
Eastern equine encephalitis- EEE
Western equine encephalitis
Flaviviridae:
Japanese encephalitis
St. Louis encephalitis
West Nile encephalitis
Bunyaviridae:
California serogroup – LaCrosse virus
What’s unique about the mode of transmission/life cycle of arboviruses?
Mosquito vector
Bite –> replicatoin in local tissue –> viremia/ hematogenous dissemination
Nonhuman animal host
Humans are dead end hosts
This means they are more common during the summer!
How do you diagnose arbovirus encephalitis?
CSF serology or PCR
Note that West Nile Virus is diagnosed with serology, not PCR, bc viral load is usually too low
What’s unique about the clinical presentation of West Nile virus?
Incubation period of 2-15 days
3-5 day flu-like fever, lymphadenopathy, maculopapular rash
1/150 develop encephalitis + myelitis (acute flaccid paralysis syndrome, asymetric weakness, decreased tendon reflexes, localized damage to anterior horn cells of spinal cord
Seizures, CN abnormalities, ataxia (lack of voluntary control of muscles), movement disorders
What does rabies virus look like?
Bullet shaped
Nonsegmented -RNA
How is rabies transmitted?
Saliva of infected animals - bite/break in skin –> virus replication in muslce cells –> infects a nerve, spreads throughout CNS
BATS, dogs in developing countries
What is indicative of rabies in histology?
Negri bodies: cytoplasmic inclusions containing lots of viral antigen
What are the 5 proteins important in rabies & what do they do?
GLMNP
G=Glycoprotein, target for antibodies
L/P = RNA polymerase (“Lumbar Puncture” of polymerase)
N= wraps RNA (Nests the RNA)
M = viral assembly (Makes the virus)
Why can you give postexposure prophylaxis for a long time with rabies?
Bc the incubation period is long (up to 1 year) and it can help, as long as the patient has not yet developed symptoms
What is the fatality rate for patients who have symptoms due to rabies?
100%s
Except one girl from Wisconsin
What’s the clinical presentation of rabies?
Asymptomatic incubation period
Flu-like prodrome of up to 2 weeks
Then you get anxiety, agitation, delerium, hypersalivation, hydrophobia (spasm of pharyngeal muscles at sound, sight, or taste of water), paralysis, seizures, coma
How do you diagnose rabies?
RTPCR of saliva
Viral antigen (i.e. biopsy of hairline of neck, CSF, cornea)
How can you prevent rabies?
Preexposure prophylaxis: 3 doses or rabies vaccine for high risk individuals
Postexposure prophylaxis: clean the bite with iodine, passive vaccination with immune globulin injected at the bite, and rabies vaccine
