 | Term | Definition |
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What is Encephalitis? |
Inflammation of brain parenchyma, leading to altered levels of consciousness |
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Symptoms of Encephalitis: |
Mild to profound lethargy to coma (and everything in b/w) |
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Associations w/ Encephalitis: |
Meningitis (meningoencephalitis); spinal cord involvement (encephalomyelitis) |
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Types of Encephalitis: |
Acute (viral; involves gray matter); Subacute (insidious onset; immunocompromised pats); Post-infectious (rare complication of viral infections; demyelinating); Slow (prion diseases) |
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Potential Sequelae of Encephalitis: |
Personality changes; Loss of physical sensations; Lack of initiative and motivation; Slowed response; Emotional problems and lack of insight; Inappropriate behavior; Poor perception, recognition and judgement; Epilepsy; Headaches; Inability to understand and communicate; Poor concentration, planning and problem solving skills; Memory problems; Physical difficulties |
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Infectious causes of Encephalitis: |
Viral (most common) - HSV1, Arboviruses, Enteroviruses; Rare - Rabies; Immunocomp pats - Toxo, HSV2, CMV, HIV, EBV (rare), JCV, VZV |
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Diagnosing Encephalitis: |
1. Imaging studies; 2. CSF findings- lympho pleocytosis, elevated protein, and normal glucose; IgM (w/ Arboviruses); PCR (for HSV) |
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What HSV1 infection can spread to the brain? |
Primary and/or Secondary infections (can often be asymptomatic) |
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How does HSV1 spread to the brain? |
Ascends the olfactory or trigeminal nerve to the brain |
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Within brain, HSV1 causes: |
Hemorrhagic necrotizing encephalitis w/ lesions in the temporal lobe, cingulate gyrus, or subfrontal region |
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To make the definitive diagnosis of HSV1: |
PCR of CSF (looking for HSV1 DNA) |
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Lab findings that point to HSV1 as cause of Encephalitis: |
MRI revealing temporal lobe involvement; CSF showing mild lymphocytic pleocytosis, mildly elevated protein, and normal glucose; PCR revealing HSV1 DNA in CSF |
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Treatment of HSV1 as cause of Encephalitis: |
IV acyclovir (70% mortality rate if untreated!!; 50% rate of sequelae occuring, even w/ tx) |
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What is an Arbovirus? |
Virus biologically transmitted by arthropod (mosquitoes [mainly in US] and ticks) |
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Pathogenesis/Manifestations of Arboviruses: |
Incubate 5-15 days; Virus replicates initially at bite site, then viremia to brain (crosses BBB), which causes rapid onset of fever and signs of encephalitis |
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What is the most common arbovirus in the US? |
West Nile Virus - characteristic to cause flaccid paralysis (myelitis) similar to polio |
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Why is WNV easily spread? |
Rapid spread occurs b/c its vector includes many mosquito species and has a broad focus range of infection |
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What are the most common symptoms of WNV? |
Fever and one other, such as weakness, nausea, vomiting, headache, change in mental status, fatigue, memory loss, difficulty walking, muscle weakness, depression |
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Factors for St. Louis Encephalitis Virus: |
Symptoms- range from febrile headache to meningoencephalitis; Vector- many species of mosquitos; Reservoir- birds!; Often occurs in outbreak fashion |
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What time of season poses the most risk of getting SLEV? |
Late summer, Early fall for humans (Birds are infected around Spring and Early summer) |
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What populations are usually infected with SLEV? |
Elderly (most seriously affected); Poor communities (live close to mosquito breeding sites; lack of air conditioning or screens on windows) |
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What is the arbovirus that causes serious infection and is first seen in horses of the area? |
Eastern Equine Encephalitis Virus (mortality 35% [70% in elderly!]) |
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What is the focus of infection for EEEV? |
East of the Mississippi river; swamps, marshes, forests (less # of mosquito species) |
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Factors for LaCrosse Virus |
aka- California Encephalitis Virus; Symptoms are mild in all ages (can cause seizures in young children); Vector is exclusively the 'tree hole mosquito' [Aedes] - stay in trees, so narrow focus of infection!; Rodents are the reservoir |
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To make definitive diagnosis of WNV: |
Detect antiviral IgM in CSF; cases occur in late summer and early fall |
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Rabies Virus - causing Encephalitis |
Most common reservoirs- raccoons, skunks, bats; Transmitted by biting |
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Pathogenesis of Rabies Virus |
Bite - Prolonged replication at bite site (~10 days) - Virus ascends sensory nerves - Fast replication in dorsal ganglia - Ascends to brain - Continued replication in salivary gland - Transmission in saliva |
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Diagnosis of Rabies Virus |
1. Index of suspicion; 2. RT-PCR, Ab in CSF, Antigen in nerve endings; 3. After death, antigen in brain and presence of Negri bodies |
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Decision for Rabies Prophylaxis |
Treat if bitten by reservior animal; consider tx if bitten by other potential reservior or unvaccinated domesticated animal (stray/pet); tx unnecessary if bitten by unlikely reservior or vaccinated domesticated animal (pet) |
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How long can one safely observe the questionable animal to determine if pat should receive Rabies Prophylaxis? |
Can safely observe for up to 10 days (b/c of slow progression at bite site!!!) |
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