Micro: Viral CNS Infections

Question 1

What are the ways in which viruses can access the CNS?

Answer 1

1. Olfactory route
2. Neuronal
3. Hematogenous

Question 2

Meningitis definition

Answer 2

Inflammation of the lining of the brain. Aseptic meningitis is NOT caused by bacteria

Question 3

Encephalitis defitinition

Answer 3

Inflammation of the brain tissues

Question 4

Meningoencephalitis definition

Answer 4

Widespread infection of the meninges and brain

Question 5

Cause of aseptic meningitis

Answer 5

Viruses, fungi, TB, infections near the CNS

- 80% enteroviruses, 10% HSV 1 and 2, 10% arboviruses

Question 6

Symptoms of aseptic meningitis

Answer 6

Mental status is normal, this can distinguish from encephalitis
- Headache, fever, chills, stiff neck, malaise, sore throut, N/V, abd pain, rash, myalgias, photophobia

Question 7

Diagnosis of aseptic meningitis

Answer 7

Elevated WBC count in spinal fluid, no bacteria

Virus may be detected in CSF

Question 8

Treatment of aseptic meningitis

Answer 8

Supportive care

Drugs exist for herpesvirus, fungal, and mycobacteria infections

Question 9

Prognosis of aseptic meningitis

Answer 9

Usually benign, resolves in 2 weeks.

Rare complication: encephalitis

Question 10

Brudzinski’s sign

Answer 10

Indicative of meningitis

- Neck is so stiff that the knees flex when the neck is flexed

Question 11

Encephalitis incidence

Answer 11

Rare, ~20,000 cases/year, mainly infants/elderly

Question 12

Causes of encephalitis

Answer 12

Exposure to virus –> influx in immune cells in brain –> cerebral edema destroys neurons –> intracerebral hemorrhage (distinguishing feature from meningitis)

Question 13

Symptoms of encephalitis

Answer 13

Altered mental status, fever, headache, vomiting, photophobia, stiff neck, confusion, sleepiness, irritability, stumbling
Urgent: unresponsiveness, coma, seizures, muscle weakness, paralysis, memory loss, flat affect, withdrawal, poor judgment

Question 14

Diagnosis of encephalitis

Answer 14

Spinal tap indicates inflammation in CSF, may be blood or virus. PCR is gold standard.

• EEG for seizures
• Brain MRI or CT may show foci of inflammation or hemorrhage

Question 15

Treatment of encephalitis

Answer 15

Supportive care and symptom relief

Antivirals for herpes, antiseizures, anti-inflammatories, sedatives

Question 16

Prognosis of encephalitis

Answer 16

Ranges from benign with full recovery to severe, fatal

Question 17

Pathogenesis of viral CNS disease

Answer 17

1. Death of neurons – cytolytic viruses can directly kill tissues
2. Host factors: age - infants/elderly. Immune status, genetics, activity
3. Acute disseminated encephalomyselitis (ADEM) - postinfectious encephalitis follows viral infection by 1-2 weeks. Associated w/ measles, mumps, VZV, influenza, parainfluenza viruses. Autoimmune.

Question 18

Herpesviruses

Answer 18

HSV2&raquo_space; HSV1

• also VZV, CMV, EMV in immunocompromised
• in weak host, CNS infections progress to severe encephalitis
• treat HSV and VZV aggressively with acyclovir

Question 19

HSV1 encephalitis prevalence

Answer 19

The most common cause of sporadic viral encephalitis (10-20% of all cases)

Question 20

HSV1 encephalitis routes of infection

Answer 20

Primary HSV1 in oropharynx –> trigem –> CNS

Recurrent HSV1 –> trigem –> CNS

Reactivation “in situ” HSV1 –> CNS

Question 21

HSV1 encephalitis symptoms

Answer 21

altered mental status, focal cranial nerve deficits, hemiparesis, slurred speech, stumbling, seizures, fever

Question 22

HSV1 encephalitis Dx

Answer 22

Gold standard: PCR of CSF for HSV and other viruses

MRI shows predominantly unilateral temporal lobe abnormalities

Question 23

Pathogenesis of rabies

Answer 23

• Transmitted by saliva via bite from rabid animal or by aerosols in caves populated by infected bats
• Replicates in muscle at bite site
• Incubation weeks-months
• Infects peripheral nerves, travels to brain
• Replication in brain causes hydrophobia, seizures, hallucinations, paralysis, coma, death
• Spreads to salivary glands from where it is transmitted
• Postexposure immunization can prevent disease due to long incubation period

Question 24

Picornaviruses transmission

Answer 24

enteroviruses are fecal-oral

Question 25

Picornavirus risk factors

Answer 25

Poliovirus –> young kids asymptomatic/mild disease, older kids + adults asymptomatic to paralytic.
Coxsackievirus and enterovirus–> neonates

Question 26

Distribution of picornaviruses

Answer 26

• Ubiquitous, poliovirus nearly eradicated

- Enteroviruses more common in SUMMER

Question 27

Vaccines or antivirals for picornaviruses

Answer 27

Poliovirus: live oral or inactivated polio vaccine

- No vaccines/antivirals for other enteroviruses, rhinoviruses

Question 28

Picornavirus dissemination

Answer 28

Replication in oropharynx and intestine –> lymph node –> blood –> skin, muscle, brain, meninges

Question 29

Togavirus examples

Answer 29

VEE, EEE, WEE, Chikungunya, Rubella

Question 30

Togavirus dissemination

Answer 30

Skin –> blood –> macrophages + spleen, lymphnodes –> brain

Question 31

Flaviviruses that cause encephalitis

Answer 31

Japanese encephalitis, West Nile, St. Louis encephalitis, Russian spring-summer encephalitis, Powassan virus

Question 32

Flavivirus dissemination

Answer 32

Mucosal surface –> lymph node –> primary viremia in blood –> vascular endothelium, macrophage, liver, spleen, lymph node –> secondary viremia causing encephalitis, yellow fever hepatitis, hemorrhagic fever

Question 33

Flavivirus transmission

Answer 33

Mosquitos, ticks

Question 34

Flavivirus distribution

Answer 34

Determined by habitat of vector: Aedes mosquito is urban, Culex is forest and urban
More common in SUMMER

Question 35

Flavivirus vaccines/antivirals

Answer 35

• Live attenuated vaccine for yellow fever and Japanese encephalitis
• No antivirals

Question 36

West Nile meningoencephalitis

Answer 36

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