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Infection 2023 > Influenza > Flashcards

Influenza Flashcards

1
Q

What are viruses?

A

Simple structures
Delivery and Payload system

Delivery system protects virus and binds to target cells

Payload contains genome and enzymes needed to initiate replication

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2
Q

Influenza summary

A 
Infection of respiratory tract (nose, mouth, throat, bronchial tubes and lungs)
Highly infectious (closed communities especially)
Most 8-10 week period in winter
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3
Q

Structure influenza

A

Orthomyxovirus - spherical
enveloped
segmented -ve ssRNA

  • 3 RNA polymerases (high error rate)
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4
Q

Outside structure influenza

A

Haemagglutinin (H) antigen - binds to cells of infected person

Neuraminidase (N) antigen - releases virus from host cell surface

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5
Q

1 segment of influenza =

A

1 polypeptide

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6
Q

Types of influenza and what species

A

A - humans, swine, equine, birds, marine mammals
B - humans
C - humans and swine

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7
Q

Influenza A involves

A

Antigenic shift AND drift
May cause large pandemics
Significant mortality for young people

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8
Q

Influenza B involves

A

Antigenic drift ONLY

Severe disease = old adults or high risk (no pandemics)

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9
Q

Influenza C involves

A

Antigenic drift ONLY

Mild disease, no seasonality

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10
Q

Most concern influenza type

A

Influenza A -
outbreaks most years
epidemics and pandemics
live and multiply in many animals (wildfowl in particular)

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11
Q

Second concern influenza type

A

Influenza B
Smaller outbreaks, less disease
Humans only
Mostly children affected

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12
Q

How does influenza replicate

A

-ve ssRNA –> +ve ssRNA
via RNA dependent RNA polymerase
–>
this produce mRNA which can make viral proteins

-ve —> +ve —> -ve produces multiple -ve ssRNA copies

these then assemble in nucleocapsid = replicated

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13
Q

How is influenza virus transmitted? 3 modes

A

Respiratory route (cough sneeze inhale)

  • small particle aerosols <10micrometre (remain in air)
  • larger particle/droplets
  • viral particles (land on surface, indirect)
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14
Q

Barriers to influenza

A

Resp epithelium = thick glycocalyx and mucus
Trap virus particles

Ciliated epithelium sweep mucus up to be swallowed (mucociliary escalator)

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15
Q

Immunological defences lung

A

Secretory IgA
Natural killer cells
Macrophages

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16
Q

How does virus enter cell?

A

Neu5Ac (NANA) residues act as receptor for Hemagglutinin antigen on virus
Invagination of virus
into Endocytosis vesicle
release virion into cytoplasm

(RECEPTOR MEDIATED ENDOCYTOSIS)

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17
Q

What is a NANA residue?

A

Sialic acid on glycoprotein/glycolipid which acts as receptor for influenza virus

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18
Q

How does virus leave cells?

A

Hemogglutinin is already attached to NANA sialic acid receptor
Neuraminidase cleaves glycoprotein + sialic receptor NANA off and allows virus to leave

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19
Q

Complications of influenza

A

Meningitis/encephalitis
Otitis media (ear infection)
Croup (young children usually)
Pneumonia

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20
Q

Time course influenza

A

Incubation - 1-5 days

Recovery time - 2-7 days

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21
Q

When can virus be found in resp secretions after initial infection?

A

As soon as 24 hours after infection

22
Q

Those at risk of serious influenza complications

A 
Children under 6 months
Older people (65+)
Underlying health conditions (resp, cardiac)
Pregnant women 
Obesity (morbid >40BMI)
23
Q

Flu during pregnancy

A

Perinatal mortality
Prematurity
Smaller neonatal size/lower birth weight

24
Q

Diagnosing infuenza

A

usually from symptoms and clinical assessment
BUT can do:
Rapid influenza diagnostic tests
PCR

25
Q

Treatments influenza

A

Antivirals
Neuraminidase inhibitors

prevention: Vaccines

26
Q

Antivirals example and explain

A

Rimantadine & Amantadine

Inhibit viral uncoating after uptake through M2 protein
for Influenza A

27
Q

Neuraminidase inhibitors example and explain

A

Oseltamivir (Tamiflu) & Zanamivir (Relenza)

Inhibit viral release from cells (cant cleave off) and cause aggregation of particles
for influenza A AND B

28
Q

Vaccines for flu

A

Both for Influenza A AND B:
Formalin inactivated vaccine injection (quadri/trivalent)

Live, attenuated, cold adapted vaccine NASAL SPRAY (quadrivalent, for children)

29
Q

What does cold-adapted vaccine mean?

A

Will only stay in upper resp tract

Cannot survive in lungs as too warm

30
Q

What does trivalent and quadrivalent mean?

A

Trivalent - contains 2 Influenza A strains and 1 B strain

Quadrivalent - contains 2 influenza A strains and 2 influenza B strains

31
Q

Neuraminidase inhibitors (TAMIFLU) come from

A

Chinese Star anise:

Shikimic acid

32
Q

Genetic changes influenza (antigenic drift)

A

Life cycle = 6 hours
Constantly replicating
Viral RNA polymerase =
high error rate, lack of proofreading = mutations

33
Q

What happens as a result of these mutations?

A

Genetic resistance and variation

34
Q

What is antigenic drift?

A 
Minor changes (natural mutations) in genes of flu virus that occur gradually over time 
Minor antigenic changes in H and N
Cause seasonal epidemics

NO VIRAL SUBTYPE CHANGE

35
Q

How does antigenic drift affect vaccines?

A

WHO monitors epidemiology and makes recommendations about strains likely to be circulating
Results in composition of virus vaccines

36
Q

How do PHE help with flu?

A

Send letters to GP’s with updates (strains, no. of cases) and details of WHO recommendations

37
Q

Other genetic changes influenza (antigenic shift)

A 
Dramatic changes in antigenic H and N properties 
Infrequent (10-20 years)
ONLY Influenza A
Change subtype (H1N1 --> H3N2)
Surface antigens from different species
38
Q

Antigenic shift defined

A

Major changes in genes that occur suddenly when two or more different strains combine
This results in NEW subtype
= widespread epidemics/pandemics

39
Q

How can antigenic shift happen?

A

Influenza viruses from different species combine in same host at same time

Reassortment of RNA segments from each species into new capsid

40
Q

Why can antigenic shift occur in Influenza A?

A

Can infect many animals - horses, pigs, waterfowl

Host infected with two different subtypes influenza (eg pig can be infected by human and avian specific viruses)

Reassortment of 2 different specie virus in one host

Has potential to spread among humans, birds and pigs

41
Q

Consequences antigenic shift

A

New subtype not seen before
= no immunity defence
Pandemics and epidemics

42
Q

Epidemic

A

Widespread occurrence of infectious disease in a community at particular time

43
Q

Pandemic

A

Epidemic over a very large area; populations all over the world

44
Q

Major Influenza type A outbreaks

A

Spanish influenza (1918 - human and avian H1N1)

Asian influenza (1957 - human and avian reassortment H2N2)

Hong kong influenza (1968 - human and avian components H3N2)

2009 Novel H1N1 (human swine and avian reassortment)

45
Q

Spanish influenza truth

A

Was actually from Kansas

But spain only place neutral in WW1 and was able to report news on flu and not on war

46
Q

Spanish flu size

A

50 million

more people died (1 year) than in 4 years of black death

47
Q

How does flu kill people? (2 methods)

A

1:
Immune system overreacts
T cells attack and destroy tissue of virus - particularly lungs

2: Opportunistic secondary infection (eg streptococcus/staphylococcus) in lungs usually

48
Q

Why do we get symptoms?

A

body’s immune response to viral invasion
Antibodies triggered and immune cells move to site of infection
Release cytokines = local inflammation

49
Q

What can occur when encountering new subtype of infleunza?

A

Cytokine storm (bird flu jumped species)

50
Q

Who does WHO recommend flu vaccine for?

A 
Pregnant women
children 6months - 5 years
elderly (>65)
people with chronic medical condition 
healthcare workers

Infection 2023 (29 decks)

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