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MICR3320 > 11 - Acute Viral Infections > Flashcards

11 - Acute Viral Infections Flashcards

1
Q

Patterns of viral infection

A
  • Acute
  • Latent
  • Persistent asymptomatic
  • Persistent pathogenic
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2
Q

Example of acute virus

A
  • Rhinovirus
  • Rotavirus
  • Influenza
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3
Q

example of latent virus

A

HSV

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4
Q

Example of persistent asymptomatic virus

A
  • Lymphocytic choriomeningitis virus
  • JC virus
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5
Q

Example of persistent pathogenic virus

A
  • HIV
  • Human T lymphotropic virus
  • Measles
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6
Q

Acute viral infections

A
  • Rapid and self limiting
  • Rapid onset of infectious virions, followed by resolution and elimination of of the infection by the host (‘clearance”)
  • Only occur when intrinsic and innate immune responses are transiently bypassed
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7
Q

Acute infections present in common public health problems

A
  • Often associated with serious epidemics affecting millions of people
  • Infected host often infectious before symptoms manifest
  • Difficult to control as by the time host is sick enough to stay home, transmission has already occured
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8
Q

Measles

A
  • Enveloped
  • Family Paramyxoviridae
  • (-) sense ssRNA, non segmented genome
  • Highly contagious disease transmitted by respiratory aerosols that triggers a temporary but severe immunosuppression
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9
Q

Symptoms of measles

A
  • Fever
  • Cough
  • Conjunctivitis
  • Maculopapular, erythematous rash
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10
Q

Complications of measles

A
  • Encephalitis
  • Ear infection
  • Pneumonia
  • Diarrhoea
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11
Q

Pathogenesis of measles

A
  • Infects alveolar macrophages and memory T and B cells
  • Clearance of MV infected cells requires destruction of these immune cells
  • Result is immunosuppression followed by loss of memory to other pathogens
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12
Q

What can maculopapular skin rash lead to

A

Severe desquamation

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13
Q

MeV infection and lymphocytes

A
  • Suppresses the proliferation of lymphocytes
  • Lymphocytes isolated from patients proliferate poorly upon ex vivo stimulation
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14
Q

Immune evasion by MeV (SSPE)

A

By cell to cell spread in neurons

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15
Q

Cell to cell spread of MEV in neurons

A
  • Transport of measles virus RNP complexes from infected neuron to uninfected cell is mediated by microfusion events at cell membrane where F proteins bind neurokinin-1 receptors (facilitates membrane fusion)
  • Viral RNP complexes accumulate at cell membrane and pass through
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16
Q

What prevents antibody detection of free Mev virus in neurons, thus promotes latency in brain

A

In neurons there is incomplete assembly of virus particles at the membrane and budding of virus does not occur

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17
Q

What is the most contagious infectious disease known

A

Measles

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18
Q

SARS-CoV-2

A
  • Linear (+) ssRNA genome
  • Family Coronaviridae
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19
Q

R0 value

A

Refers to the contagiousness and transmissibility of infectious pathogens

20
Q

R0 value of SARS-CoV-2

A
  • 4.9
  • Twice as transmissible as influenza
21
Q

Viral dissemination into body organs

A
  • Initial replication takes place in upper respiratory tract, followed by migration of virus to lungs
  • Primary viremia occurs after establishment of infection and replication in lung pneumocytes
  • This viremia disseminates the virus throughout the body via blood stream where another cycle of viral replication takes place, thus leading to further dissemination
22
Q

Respiratory Syncytial Virus

A
  • Orthopneumovirus (group 5)
  • (-)ssRNA, non segmented
  • Filamentous, enveloped virion
  • Close contact and aerosol transmission
  • Infects nearly all children by 2 years of age
  • ~60,000 deaths p.a under <5yo
23
Q

RSV initial replication

A

In nasopharynx and upper respiratory tract and may spread to small bronchioles or alveoli of lower resipratory tract

24
Q

RSV infection of epithelial cells

A
  • Elicits widespread transcriptomic and proteomic changes, which both mediate the host immune responses
  • RSV can circumvent the host stress responses, including apoptosis
  • Result is to severely impact human lungs, resulting in airway remodeling and pathophysiology.
25
Q

Antigenic groups of RSV

A

GRoups A and B

26
Q

Anti-RSV antigenicity and immunity

A
  • Neutralising antibodies to
    F and G proteins develop soon after infection with RSV groups A and B
  • Duration of immunity is
    short-lived (re-infection
    upon challenge with the heterologous subtype occurs within 2 months)
  • Within 26 months 73% experience two or more, and 47% experience three or more infections
27
Q

RSV pathogenesis

A
  • Restricted to superficial cells of respiratory epithelium
  • Giant cells with round, pink intracytoplasmic inclusions seen in tissues
  • Tropism largely limited to humans (transmission
    between animals and in populations does not
    occur - semi-permissive)
  • However, infection of and transmission among chimpanzees is sustained
28
Q

Cells infected by RSV

A

Cells from trachea, bronchi, and bronchioles

29
Q

Viral factors of RSV

A
  • G protein
  • F protein
  • NS1 and NS2
  • Viral strains and isolates
  • Viral load
30
Q

G protein

A

Glycosylation, sG neutralising antibodies avoidance

31
Q

F protein

A

Conformational change, infectivity and protection

32
Q

NS1 and NS2

A

IFN-1 inhibition

33
Q

Host factors of RSV

A
  • Male
  • Lung and heart anomalies
  • Low vit D level
  • Inadequate immune system
  • ?Genetic polymorphism
34
Q

Environmental factors of RSV

A
  • Exposure to smoke
  • Air pollution
  • Winter
35
Q

Patients who develop severe RSV infections

A

Undergo exaggerated cell mediated immune response (e.g. increased granzyme B and cytokine release) and/or improper immune regulation

36
Q

Hemophagocytic lymphohistiocytosis
(HLH)

A

Fail to undergo normal immune contraction and require immunosuppression to prevent death

37
Q

Dengue virus genus and family

A

Orthoflavivirus genus of Flaviviridae family

38
Q

Mosquito that carries dengue

A

Aedes aegypti infected by feeding on a person in viraemic phase of infection

39
Q

Dengue lifecycle

A
  • During the extrinsic phase of the cycle, dengue viruses first infect mosquito midgut cells and other tissues before
    disseminating to the salivary glands
  • An infected mosquito can then transmit the dengue virus to several humans as it
    feeds or attempts to feed
  • Once infected, it takes an average of 4–7 days for the onset of symptoms and for a
    person to become capable of transmitting dengue virus to a new mosquito
  • Both symptomatic and asymptomatic individuals can transmit dengue virus to mosquitoes
40
Q

Four distinct dengue viruses

A

DENV 1-4

41
Q

Dengue Virus

A
  • Linear (+) ssRNA genome (group 4)
  • Each serotype includes several genotypes
  • Infection with one serotype is confers lifelong immunity to that serotype but not to the other three serotypes
  • People who live in dengue endemic areas can be infected up to four times
    in their lifetimes
  • Re-infection (with a different serotype) is associated with more severe disease
42
Q

What is clearance of DENV antigens and genome associated with

A

Development of adaptive immune response

43
Q

Diagnosis of DENV

A
  • Non-structural 1 (NS1) antigen and antibodies change over time
  • Thus different diagnostic tests will be appropriate depending on the stage of infection (e.g. ELISA, RT)
44
Q

Levels of IgM and IgG in primary dengue infection

A

IgM peaks first then IgG

45
Q

Levels of IgM and IgG in secondary dengue infection

A

IgG peaks first and much higher then IgM

46
Q

Factors involved in control of dengue

A
  • Immune status
  • Viral strain
  • Genetic status
  • Age

MICR3320 (14 decks)

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