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Clinical Micro > Viral CNS infections > Flashcards

Viral CNS infections Flashcards

1
Q

What is encephalitis and how is it different from meningitis? What are some symptoms?

A

inflammation of the brain itself - meningitis symptoms + mental status changes

seizures, decreased consciousness, confusion

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2
Q

What is myelitis?

A

focal neurological signs localized to spinal cord

- inflammation of the white/grey matter of the spinal cord

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3
Q

What are some results from a CSF sample that would indicate that you have a viral meningitis case? (4)

A
  1. Gram stain negative
  2. Lymphocytic pleocytosis (increase) (WBC 100 to 1,000)
  3. Occasionally increased red blood cells (RBC) (ex: HSV)
  4. Increased protein, normal glucose
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4
Q

What is the typical presentation of a viral meningitis infection?

A
  1. typically acute (except with rabies but that’s more encephalitis)
  2. healthy people are affected but it is more common in immunocompromised individuals
  3. Frequently occurs as meningoencephalitis
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5
Q

What is meningoencephalitis?

A

condition that simultaneously resembles both meningitis and encephalitis

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6
Q

What are 4 main viral causes of CNS infections?

A
  1. Enterovirus
  2. HSV-1 and HSV-2
  3. Arbovirus
  4. Rabies
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7
Q

What are 4 (less common) viral causes of CNS infections

A
  1. Other herpes viruses like EBV, VZV, CMV
  2. Measles virus
  3. Lymphocytic choriomeningitis virus (LCMV)
  4. Human immunodeficiency virus (HIV)
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8
Q

What family does Enterovirus belong to? what are 2 other members of this family?

A

Picornaviridae

Other members: rhinovirus and hepatitis A

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9
Q

What is the genome/structure of Enterovirus

A

ssRNA (+ sense) and non enveloped

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10
Q

What kind of virus is enterovirus

A

A respiratory virus

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11
Q

What % of viral meningitis is caused by Enterovirus?

A

30-50%

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12
Q

What are the typical clinical manifestations of a CNS infection by Enterovirus? How long? Is the infection widespread or tissue localized?

A

Usually respiratory symptoms with severe headaches and photophobia that can last for over a week

Can infect lots of different tissues

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13
Q

are there antivirals/ a vaccine for Enterovirus?

A

no

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14
Q

What are the steps of diagnosing someone with a CNS infection with Enterovirus?

A
  1. Clinical suspicion/epidemiology
  2. CSF specimen profile (normal glucose and high protein)
  3. do RT-PCR on the CSF specimen
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15
Q

What is the treatment for someone with a CNS infection with Enterovirus?

A

just symptom management - pain control and hydration

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16
Q

What family of virus do HSV-1 and HSV-2 belong to?

A

Herpesviridae

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17
Q

What type of genome/structure do HSV1 and 2 have?

A

dsDNA and enveloped

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18
Q

HSV-1 and HSV-2 are the most common cause of..?

A

sporadic viral encephalitis in North America

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19
Q

do HSV 1 and 2 show seasonal distribution?

A

no, sporadic

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20
Q

What is the mortality rate of encephalitis infections with HSV (without treatment)

A

high, around 70%

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21
Q

What is most commonly the cause of the encephalitis pathogenicity of HSV?

A

not usually the primary exposure (mucocutaneous, oral/genital) but reactivation (from latency in sensory ganglion)

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22
Q

What are some symptoms of HSV caused encephalitis? (4)

A
  1. Fever/headache
  2. Neurological changes/ focal symptoms (ie. temporal lobe will light up on examination)
  3. Seizures and mental status changes frequent
  4. Long-term neurological sequelae possible
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23
Q

What can result in a fatal dissemination of HSV throughout the body?

A

Immunodeficiency

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24
Q

Temporal lobe activation on an MRI is consistent with…

A

HSV encephalitis

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25
Q

Where does HSV establish a latent/dormant stage?

A

in the trigeminal ganglion

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26
Q

At what stage: primary infection, latency, and reactivation, is a CNS infection likely to occur?

A

Reactivation

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27
Q

HSV-2 (genital herpes) establishes a latent infection where?

A

in the dorsal root ganglia

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28
Q

How does HSV-2 cause encephalitis?

A

Because the dorsal root ganglia are so closely associated with the spinal cord, HSV can infect there and travel up to the brain

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29
Q

What are some rough diagnostic steps in determining a CNS infection with HSV?

A
  1. Clinical suspicions
  2. Diagnostic imaging –> MRI looking for temporal lobe activation
  3. CSF profile
  4. PCR of the CSF
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30
Q

What is useless in terms of tests for determining a CNS infection with HSV? why?

A

Serology because the patient will already have circulating antibody from the initial infection

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31
Q

What would the CSF profile of someone with an HSV CNS infection look like? (what 3 things is it high in)

A

High lymphocytes, increased RBCs common, high protein

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32
Q

What is the treatment for a suspected HSV CNS infection?

A

antivirals (acyclovir)

- given empirically if infection suspected

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33
Q

What is the first step in the activation of acyclovir?

A

Phosphorylation by viral kinase ( thymidine kinase)

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34
Q

What are the next two activation steps of acyclovir? what does them? what is the end product?

A

phosphorylation by two host kinases, end product is a triphosphate (nucleotide analogue).

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35
Q

What happens once the acyclovir is in the active form?

A

incorporated into the growing nucleic acid and halts elongation process

36
Q

What are two points of resistance that viruses can develop to acyclovir?

A

HSV thymidine kinase or HSV DNA polymerase mutations

37
Q

What are two alternate drugs to acyclovir? why is either of them used?

A
  1. cidofovir (TK not required)

2. foscarnet (pyrophosphate analog)

38
Q

What does Arbovirus mean?

A

arthropod borne virus

39
Q

What are two major vectors of arboviruses?

A

Mosquitos and ticks

40
Q

How many registered arboviruses are there? how many of them are human pathogens?

A

over 500 registered

over 130 are pathogenic to humans

41
Q

What is a vector?

A

biting insect or tick (usually) that transmits a disease/parasite from one animal to another

42
Q

How many virus families are there in the Arboviruses?

A

6

43
Q

What were the 3 families of arboviruses we mentioned in lecture? What type of genome do they each have?

A
  1. Flaviviruses (ssRNA +)
  2. Togaviruses (ssRNA -)
  3. Bunyaviruses (ssRNA -)
44
Q

What are 6 important members of the Flavivirus family?

A

Zika, Dengue fever, Yellow Fever, West Nile, St. Louis encephalitis, Japanese encephalitis virus

45
Q

What are 3 important members of the Togavirus family?

A
  1. Eastern equine encephalitis virus (EEE)
  2. Western equine encephalitis virus (WEE)
  3. Chikungunya virus
46
Q

What are 2 important members of the Bunyavirus family?

A

La Cross Virus

Rift Valley Fever Virus

47
Q

What 4 arboviruses cause Encephalitis in humans ?

A

West Nile virus (WNV)
Japanese encephalitis virus
Eastern equine encephalitis virus
La Crosse virus

48
Q

What are 2 primary symptoms/clinical manifestations of an Arbovirus infection

A
  1. typically starts of with vague “viral syndrome”

2. Can progress to fever, headache, seizures

49
Q

What kind of CNS inflammation is common with Arboviruses?

A

Typically presents as a meningoencephalitis

50
Q

What impacts the severity and incidence of arbovirus CNS infection?

A

depends on both the virus and the host

51
Q

What kind of distribution do arboviruses have? What controls this?

A

Both seasonal and geographical

Based on distribution of both host and reservoir

52
Q

What is a reservoir?

A

An organism or population that directly or indirectly transmits a pathogen while being virtually immune to its effects

53
Q

During what season do you tend to see high instances of arbovirus infection?

A

Seasons with lots of rain b/c more rain = more mosquitos

54
Q

In the Epidemic (or urban) cycle, who acts as the reservoir?

A

humans

55
Q

In the Epidemic (or urban) cycle, who acts as the vector? What are 2 examples of viruses

A

mosquito: A. aegypti for dengue and yellow fevers

56
Q

In the Ezoonotic (sylvatic or jungle cycle), who acts as the reservoir?

A

tend to be a vertebrate - harbours the virus with no ill effects

57
Q

In the Ezoonotic (sylvatic or jungle cycle), who acts as the vector? What effect does this have?

A

Mosquito: A. aegypti

tends to amplify the virus as the reservoir hosts are not affected

58
Q

In the Ezoonotic cycle, how do humans fit in?

A

Incidental hosts

59
Q

When humans are acting as incidental hosts, can there be human to human spread? Can it be passed to vectors again?

A

No person-to-person spread

Viremia not sufficient in humans to be picked up by the insect vectors

60
Q

What is an example of a virus spread through an ezoonotic cycle?

A

West nile virus

61
Q

What is the reservoir for WNV?

A

birds

62
Q

In the Epizoonitic (rural) cycle, who acts as the reservoir?

A

wild birds

63
Q

In the Epizoonitic (rural) cycle, who acts as the vector?

A

Culex sp. mosquito

64
Q

In the Epizoonitic (rural) cycle, where is the virus normally being passed between?

A

Between the domestic animals and the vector

65
Q

in the Epizoonotic cycle, where do outbreaks normally occur?

A

in the animals

66
Q

In the Epizoonotic cycle, who acts as the amplifying host?

A

humans

67
Q

What are 3 examples of viruses spread through an Epizoonotic cycle?

A
  1. Japanese Encephalitis Virus (JEV)
  2. Western Encephalitis Virus (WEV)
  3. St. Louis Encephalitis Virus
68
Q

What 3 factors are considered in making a diagnosis of an arbovirus infection? What testing can be useful?

A
  1. Clinical suspicion - social history/exposure/travel
  2. CSF profile
  3. CSF PCR and serology can be useful
69
Q

What would be expected from a CSF sample of someone infected with an arbovirus?

A

High WBC count and high protein

70
Q

What treatment is given to someone with an arbovirus CNS infection?

A

Largely supportive, pretty much always fatal

71
Q

What two arboviruses are there vaccines for? what type of vaccine are they?

A
  1. JEV - inactivated vaccine

2. Yellow Fever Virus - live attenuated

72
Q

What are two forms of more large scale prevention of arboviruses?

A
  1. Control of vector (mosquito)

2. Personal protection: Insect repellent/nets/clothing

73
Q

What family of viruses does Rabies belong to? What type of genome and structure does it have?

A

Family: Rhabdoviridae

Large enveloped virus, ssRNA (-)

74
Q

Rabies is most common in…?

A

developing nations - poor rural communities, mostly in Africa and Asia

75
Q

What is the mode of transmission of rabies

A

Through the bite of an infected animal, the virus is in the saliva

76
Q

What are common vectors of Rabies in North America

A

bats, skunks, raccoons, and foxes

77
Q

What is a behavioural trait of rabies infected animals?

A

Show no fear to humans, act very agitated

Also are scared of water

78
Q

What does rabies virus have a high affinity for? What is the term for this ?

A

neurotropic – has affinity for nerve cells or tissue

79
Q

What tissues are infected following an bite from a rabid animal ?

A

brain (eventually), salivary glands and sensory nerves to skin are infected

80
Q

What is the progression of Rabies virus like in humans?

A

Long incubation period (weeks)
Temporal pattern of presentation
- ie. time it takes to develop severe neurological symptoms will be dependent on how far away the bite site is from the brain

81
Q

What are 4 symptoms of a rabies infection?

A
  1. Fever
  2. Agitation
  3. Hydrophobia = fear of water
  4. Painful spasms followed by excessive saliva
82
Q

Where is the best place to take a biopsy for a rabies test?

A

the skin at the back of the neck

83
Q

What two types of tests are done on rabies test specimens?

A

PCR and DFA

84
Q

When is serology useful for rabies testing?

A

to test and see if someone is immune or not

85
Q

What is the treatment for a suspected rabies infection?

A

washing of the wound site and injection of preformed anti-rabies antibodies

Clinical Micro (28 decks)

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