CNS Infections- Viral Encephalitis Flashcards
During encephalitis, viral replication occurs in ______, leading to severe CNS dysfunction which causes manifestations.
brain parenchyma
The brain is not a ____ for viral infection. Infections in the CNS are usually a secondary infections, occurring weeks, months, years after the initial infection.
POE
Few survive viral encephalitis, and those who do have ___________
serious emotional disorders and learning deficits
The most frequent etiologic agents are
- Arboviruses
2. Herpes simplex virus-1 (HSV-1)
The etiologic agents that can cause BOTH focal and diffuse encephalitis:
- Non-polio enterovirus
- Herpes simplex virus 1 (HSV-1)
- Arbovirus
The etiologic agents of FOCAL encephalitis only:
rarely polio virus or rabies
Describe Arbovirus
- Arthropod-borne viruses (arboviruses)
- Zoonotic agents
- Association with chronic infection in the reservoir host.
- Humans are generally the dead end host.
- Disease in the reservoir, if it occurs, is similar to human disease if POE is same
Togaviridae group comprises most arthropod-borne viruses and Rubella, also includes:
Alphavirus and Flavivirus
Alphavirus includes
- Eastern equine encephalitis (EEE) is caused by EEEVirus.
- Western equine encephalitis (WEE) is caused by WEEVirus.
- Venezuelan equine encephalitis (VEE) is caused by VEEVirus.
* *equine viruses**
Flavivirus (flavi = Latin for yellow, includes yellow fever, dengue, hepatitis C agents, also Japanese encephalitis virus and Nipah virus which are an important disease agents in Asia; includes:
- St. Louis encephalitis (SLE) is caused by SLEVirus.
- West Nile Encephalitis (WNE) is caused by WNVirus.
- Powassan encephalitis (POW) is caused by POWVirus
Bunyaviridae - bunyavirus includes:
- California virus
- Jamestown canyon virus
- La Cross viruses (LAC) virus
(called the California encephalitis group, highest incidence in California, Midwest and southeast US)
Reoviridae group (respiratory, enteric orphans) includes:
- Rotaviruses
2. Coltiviruses–> Colorado tick fever is caused by CTFVirus (rare in US)
Arboviruses cause two primary syndromes in humans:
- hemorrhagic fever
2. encephalitis/meningitis
Arboviruses are the primary cause of _________, but also cause _________.
epidemic encephalitis
benign, aseptic meningitis
Seasonality
summer months when humans are outdoors.
Vectors are primarily
mosquitoes and ticks
- Colorado tick fever and Powassan fever virus are spread by ticks
- The rest of the arboviruses are spread by mosquitoes
Reservoir
Zoonosis (many animals, but primarily birds and small mammals in US)
Survival of virus by alternating between vertebrate host (reservoir) and arthropod host (vector)
Primary virus replication (viremia) occurs with each arbovirus having specific target cells, such as endothelial cells of the capillaries, macrophages, monocytes, erythrocytes, and the reticuloendothelial system (liver, spleen, lymph nodes) → symptoms are _________
either no or mild symptoms
A second round of replication in reticuloendothelial cells can occur immediately after the primary round, producing a second viremia, which may yield sufficient virus to attack___________, depending upon the specific virus → symptoms are __________
brain, liver, skin, vasculature, kidney
symptoms are severe
In humans, during the first and second rounds of replication, the viremia is usually low, resulting in mostly ______________
asymptomatic infections and humans being incidental hosts.
Asymptomatic infections are the most common*
S/S
Mild, self-limiting flu-like illness (1 of 5 persons infected) lasting about 1 week, URT symptoms (coryza), fever, chills, sore throat, headache, nausea, vomiting, muscle weakness &/or myalgias, arthralgias, maculopapular rash.
CNS disease may manifest as
- Mild, self-limiting aseptic meningitis.
- acute, fulminant, diffuse, encephalitis (can be focal) and death.
- +/- acute flaccid paralysis
will see signs of meningoencephalitis: lethargy, irritability, drowsiness, acute flaccid paralysis, seizures, may evolve into coma, then death due to immunopathology (brain edema) and/or myocarditis
Differential
- Arboviruses
2. enteroviruses
3. herpes viruses.
4. rabies virus (dumb rabies)
CSF sample will show
protein and glucose levels as per viral infection and mononuclear pleocytosis.
Treatment/Prevention
Treatment is supportive
Prevention goal: limiting the vector population
US military has human vaccines for Eastern Equine Encephalitis and Western Equine Encephalitis
Eastern Equine Encephalitis (EEE):
- vectors are mosquitos
- This disease has worst mortality rate; survivors are more likely to manifest with serious neurological sequelae
- *Of all arbovirus agents of encephalitis, EEEV is unique in that infection often (not always) causes EEE. Asymptomatic infection is NOT the norm!!**
Western Equine Encephalitis (WEE):
- vectors are mosquitos
- rural residence is highest risk factor
- Most benign form of encephalitis*
St. Louis Encephalitis (SEE):
- vectors are mosquitos
- Midwest
- Leading cause of epidemic arboviral encephalitis in US before West Nile Virus epidemic in 2002
West Nile Encephalitis (WNE):
IMPORTANT
- Closely related to St. Louis encephalitis (cross-reacts serologically with SLE)
- *Most common arbovirus infection in the US today**
Transmission of west nile besides mosquitoes
- Transfusions (4 cases)
- in utero
- case of a women with WNE passed infection to child via breast milk
- Organ transplants
S&S of WNE
- flu-like symptoms (moderate to high fever or chills, anorexia, malaise, muscle aches, joint pain, respiratory symptoms)
- nausea, vomiting, diarrhea
- maculopapular rash spreading from the trunk to head and limbs
- frontal headaches of >7days duration
- eye pain
West Nile Encephalitis is West Nile fever with S/S of one or more of the following
- meningitis
- encephalitis
- parkinsonism – tremors (obviously not in limb(s) with flaccid paralysis)
- Focal symptoms of muscle weakness/ascending, asymmetrical diffuse flaccid paralysis:
- diminished deep-tendon reflexes/areflexic leg weakness,
- EMG velocity studies demonstrate axonal-type polyneuropathy affecting anterior horn cells or their axons vs. demyelination
- No muscle or sensory pain/loss is noted
Treatment for WNE
Ribavirin is efficacious in vitro (in cell culture) studies
During WNE in CSF you’ll see
plasma cells
California (CAL) Encephalitis Serogroup
- La Cross (LAC; Midwestern, Southeastern US) is the most important cause of arboviral pediatric encephalitis in the USA
- Jamestown canyon and other CAL groups rarely cause disease in humans
- Seizures may occur during illness, some patients who recover from illness will experience seizures as sequelae
