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respiratory Flashcards

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USMLE® Step 1 flashcards
1
Q

How many types of influenza are there?

A

4 types

A, B, C, D

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2
Q

Who can type A influenza infect?

A

humans, birds, pigs and other animals

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3
Q

What type can cause pandemics?

A

Type A only

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4
Q

What type can cause seasonal epidemics?

A

Type A and B

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5
Q

Who can type B infect?

A

humans and seals

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6
Q

Who can type C infect?

A

humans and dogs

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7
Q

Who can type D infect?

A

pigs and cattle

no known human infections

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8
Q

What does haemagglutinin (HA) bind to?

A

binds to cell surface (sialic acid in the host epithelial cells of the respiratory tract)

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9
Q

Role of haemagglutinin

A

Responsible for virus penetration, mediates fusion between virus and cell
Involved in immune response

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10
Q

Role of neuraminidase (NA)

A

Assist in virus release from cell

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11
Q

What is present on the lipid membrane of the influenza A virion

A

HA, NA and M2 protein

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12
Q

How many different types of HA and NA types of capsid proteins are there?

A

18 HA

11 NA

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13
Q

How are influenza A classified

A

Based on HA and NA
3 HA types
2 NA types

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14
Q

How are influenza B classified

A

Victoria and Yamagata

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15
Q

Full nomenclature for influenza classification

A

Group, Location, Year of isolation

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16
Q

What types of cells do influenza infect

A

Epithelial cells of respiratory tract

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17
Q

Transmission of influenza amongst human-human

A

direct contact-inhaling respiratory droplets

indirect contact with fomites (touch eyes, nose or mouth)

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18
Q

What is the incubation period for influenza

A

2 days (range 1-4)

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19
Q

When does the virus shed

A

Present before disease onset

Continues 2-5 days post resolution of symptoms

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20
Q

Natural reservoir of influenza

A

Wild waterfowl, domestic ducks, chickens, horses, pigs

21
Q

Source of influenza A viruses

A

Start as avian influenza viruses and then become endemic

22
Q

How does animal-animal transmission of influenza occur

A

Virus shed in saliva, nasal secretions and faeces

23
Q

How does transmission between animal-human occur

A

contact with infected livestock (poultry and pigs)

24
Q

What leads to evolution of new influenza strains (seasonal epidemic)?

A

Antigenic drift
Replication of RNA genome is error prone and leads to amino acid mutations
Mutations in antigenic regions allows virus to escape from neutralisation by antibodies from prior infections/vaccination
New variants results in seasonal epidemics

25
Q

What leads to the creation of pandemic viruses?

A

Antigenic shift
This is through reassortment (the exchange of RNA between viruses inside a host cell).
Two viruses co-infect a cell and pool their genetic material creating numerous, genetically diverse, progeny viruses

26
Q

Which population has the highest notifications and hospitalisations?

A

elderly and children <5 years

27
Q

Diagnosis

A

Nose or throat swab
Electron microscopy: morphological appearance
Isolate in culture and perform rapid antigen tests
PCR

28
Q

What diagnostic method allows us to type and subtupe the viral strain?

A

PCR
Type A or B
HA and NA subtypes
Test for resistance mutations

29
Q

What are the two classes of drugs that can be used to treat influenza?

A

Neuraminidase inhibitors

Adamantanes (M2 ion channel blockers)

30
Q

Name NA inhibitors

A

Tamiflu-Oseltamivir (oral)
Relenza-Zananmivir (oral inhalation)
Resistance developing to Tamiflu

31
Q

Are NA inhibitors active against type A and B

A

YEs

32
Q

Are Adamantanes active against type A and B

A

No only against influenza A

2 drugs” Amantadine and Rimantadine

33
Q

Vaccine composition for influenza

A

Annual vaccines that protect against currently circulating strains. Decision made by WHO committee.

34
Q

What is a key requirement for vaccine strains in

vaccine production?

A

Must grow well in eggs to meet the high demand for vaccine doses

35
Q

How are the desired HA and NA strains produced?

A

Strains with desired HA and NA genes undergo reassortment with egg-adapted strains, which are then
purified and inactivated

36
Q

What are the conditions required for a pandemic

A

Emergence of new subtype A strain
New virus infects and spreads efficiently in humans
New virus causes serious illness and death
Subtypes have not circulated for a long time, thus little to no immunity to new virus

37
Q

Spanish flu (1918-19) subtype

A

H1N1

38
Q

How much of the world’s population was affected by the Spanish flu

A

50% (40-50 million deaths)

39
Q

Did co-infections occur in people infected with Spanish flu

A

Yes in 95% of deaths during this pandemic

Bacterial (S. pneumoniae)

40
Q

What age group did the Spanish flu affect

A

20-40 years old

41
Q

Asian flu (1957-58) subtype

A

H2N2

42
Q

How did Asian flu subtype emerge?

A

Antigenic shift

H1 to H2

43
Q

What age group did Asian flu affect the most

A

Highest infection rates: School children (aged 5-19)

Highest death: elderly

44
Q

Hong Kong flu (1968-69) subtype

A

H3N2

45
Q

How did Hong Kong flu subtype emerge?

A 
Antigenic shift (reassortment between seasonal H2N2 and avian influenza viruses)
H2 to H3
46
Q

Swine flu (2009) subtype

A

H1N1

Started in Mexico and spread globally

47
Q

What age group did Swine flu affect the most

A

Children and young adults aged 12-22

48
Q

Co morbidity associated with swine flue

A

secondary bacterial pneumonia

49
Q

Why is transmission of avian strains to human rare?

A

sialic acid receptors are different
receptors for human viruses are alpha-2,6-linked sialic acid
receptors for avian viruses are alpha-2,3-linked sialic acids

medical micro (2 decks)

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