Viral Infections of CNS Flashcards
Viral meningitis
a viral infection associated with acute onset of meningeal symptoms (classic triad)
aseptic meningitis
short lived, self limited, CNS syndrome characterized by meningeal symptoms and a sterile CSF
What are the most common cause of aseptic meningitis cases
viruses
Viral encephalitis
inflammation of brain parenchyma caused by a virus
- usually a complication of viral meningitis
Viral encephalitis accounts for what percent of confirmed encephalitis cases?
70%
viral myelitis
inflammation of the spinal cord due to a virus that can be diffused or localized to a specific region
- usually acute
- involvement with spinal nerve roots or PNS is referred as myeloradiculitis
Viral infections of CNS, 7 forms of infection
- Viruses are either inhaled (Mumps), ingested (non-polio Enteroviruses), or injected (arboviruses)
- Infect the oropharyngeal, gastrointestinal, or skin-associated lymphoid tissues
- Viruses gain entry to CNS by directly infecting BMECs, through infected immune cells that cross into the brain, or migration through peripheral sensory or motor neurons
- Usually meningeal cells are infected first= results in inflammation and meningeal syndrome of symptoms?
- Intact adaptive response is required to control and clear the infection
- Without proper immune control can spread to parenchyma of brain and spinal cord
- Treat the symptoms =antiviral treatment only if effective drug exists
Viral meningitis facts
Most common cause of meningitis - incidence unknown given that most cases are self-limited and go unreported
Enteroviruses cause vast majority of cases—(Coxsackie viruses 🡪 hand-foot-and-mouth disease)
Other common ones: Arboviruses (arthropod-borne viruses), and HIV
Less common: lymphocytic choriomeningitis virus (LCV), Cytomegalovirus (CMV), type II herpesvirus (HSV-2), Measles virus, Mumps virus, Epstein-Barr (EBV), and influenza viruses
Usually preceded by flu-like respiratory, gastrointestinal, or joint/muscle pain symptoms (depending on the viral route of
infection)
Non-polio enteroviruses
- up to 61% of cases (90% in countries with mumps vaccinations)
- > 110 genetically distinct enteroviruses have been identified
- Seasonal - tend to manifest in late summer and early autumn
- No specific antiviral therapy exists
- ~99% of cases is self-limiting and involves complete recovery
- In the < 1% that results in death, brainstem inflammation is almost always involved
Risk factors: neonates and infants, summer months, day care setting
Routes of CNS entry similar to all: direct interactions with BMECs, Trojan horse transit, inflammation-induced
Most common identified cause (except in places without Mumps immunization programs)
Name derived from site of entry and replication: oral-fecal route
Seasonality in temperate regions; year-around in tropics
~60% of all identified cases
How do non-polio enteroviruses enter CNS
- Target multiple receptor for entry, including ones in BMECs
- Trojan horse transit is possible
- Neurons (and neural stem cells) highly susceptible to infection
- Latency and reactivation!
- Depending area of entry=meningitis or encephalitis
Arboviruses
viral meningitis
< 1% of cases (healthy individuals will restrict infection to meninges)
Immunosuppressed individuals cannot, will disseminate= encephalitis
WNV, zika, chikgunya, dengue
Routes of CNS entry similar to all: direct interactions with BMECs, Trojan horse transit, inflammation-induced
Show seasonality but also specific
geographical areas
Transmitted by mosquitoes
Mumps, HIV and others
viral meningitis
Mumps, HIV, herpesviruses
Various routes of transmission: airborne, sexual, direct contact with infected fluid
Worldwide, year-round
~15% mumps, ~7% HIV
Routes of CNS entry similar to all: direct interactions with BMECs, Trojan horse transit, inflammation-induced
Complication of viral meningitis
clinically encephalitic syndrome
- progressive impairment of consciousness, seizures, mood and behavioral changes and focal neurologic signs (memory and orientation)
causative agents of viral encephalitis
hundreds of them
usually arboviruses are epidemics, while other are sporadic
- many etiology unknown
At risk groups for viral encephalitis (6)
- extreme ages
- immunosuppression
- direct animal contact
- recreational activities that put you in contact with insects
- vaccination status
- geographical area and season
Why is molecular diagnosis imp for viral encephalitis
- Molecular diagnosis is important=PCR and multiplex PCR
- Multiplexing allows for screening of multiple pathogens simultaneously
- Usually indicative of the infection, but other studies need to be considered
- CSF analysis: ↑ lymphocytes, normal glucose, moderate to ↑ protein
- Neuroimaging: cerebellar lesions, focal lesions in basal ganglia, subependymal, temporal and/or frontal lobe enhancement, white matter abnormalities
Treatment for viral encephalitis
- treatments are primarily supportive
- one exception is HSV encephalitis (acyclovir)
- if viral encephalitis is suspected, acyclovir should be started empirically
what is the most common cause of nonepidemic encephalitis
herpes viruses
acyclovir
Acyclovir only works on viruses of the Herpes family, mostly used for Herpes simplex infections
Viral myelitis characteristics
- Usually there is involvement of meninges or brain parenchyma, but for a few myelitic syndrome is the dominant feature
- Most viruses will cause acute myelitis, a few transverse myelitis
- Acute =grey matter only, more diffuse area affected
- Transverse (TVM) = grey and white matter, usually restricted to a whole cross-section of the spinal cord, hence dysfunction below the level affected while function above such level is normal
- Clinical features are mostly determined by the location and extent of the injury rather than by the viral agent
- Laboratory tests to identify agent are critical
Examples of Viral Myelitis
HSV, varicella zoster virus, chicken pox, CMV, EBV, poliovirus
Best treatment for viral infections of CNS
vaccines
- very few antivirals
- herd immunity helps to prevent outbreaks and protects susceptible groups
