42. Viral Disease Outbreak 2 Flashcards
1
Q
Define ‘outbreak’
A
occurrence of large number of cases of disease in short period of time
2
Q
Define ‘epidemic’
A
- occurrence of disease in unusually high numbers in localised population
3
Q
Define ‘pandemic’
A
when disease is prevalent throughout world
4
Q
Explain influenza
A
- acute respiratory infection caused by influenza viruses
- very contagious
- seasonal infection - peaks October -May
- varies in impact due to circulating strains and vaccine composition
5
Q
Transmission of influenza
A
- air droplet secretions
- aerosol
- direct contact with respiratory secretions of infected
6
Q
Structure of influenza
A
- orthomyxoviridae
- enveloped virus
- segmented genome - RNA virus
- non-geometric capsid
7
Q
Key proteins in influenza
A
- haemagglutinin - facilitates attachment and entry of virus to host cells
- neuraminidase - facilitates release and exit of virus from host cells
8
Q
How is influenza classified?
A
- on haemagglutinin and neuraminidase subtypes
- H1N1 - spanish flu
- H5N1 - bird flu
for example
9
Q
Viral replication of influenza
A
- synthesis of virus mRNAs and replication of viral genome occurs in nucleus
- viral mRNAs made and translated
- replication of 8 genomic segments and progeny nucleocapsids assembled
- nucloecapsids move from nucelus to cytosol
- release by budding, giving rise to extracellular viral particles
- viral release by N proteinv
10
Q
2 phenomena responsible for variation in flu over time
A
- antigenic drift
- antigenic shift
11
Q
What is antigenic drift?
A
- minor antigenic changes in H and N proteins that occur each year
12
Q
What is antigenic shift?
A
- more dramatic change in antigenic properties of H and N proteins and changes in subtype from H1N1 to H3N2 for example
- infrequent and can lead to new, more virulent virus
- impacts outbreaks either epidemic or pandemic
13
Q
Consequences of antigenic variation in flu
A
- appearance of new subtypes of virus or subtypes that havent circulated for years
- individuals in pop have not encountered this subtype
- individuals in pop are immunologically unprotected
14
Q
Molecular basis of antigenic variation
A
- reassortment of viral RNA segments
- new viruses can be generated from ‘parent’ viruses
- all 8 of influenza RNA genome segments can undergo this
- antigenic shift - RNA segments responsible for H and N proteins
- reassortment across species
15
Q
Human flu pandemics occur every … years due to …
A
- 10-40
- major genetic changes in influenza A virus genome
16
Q
Overview of Spanish flu
A
- 1918-1919
- appearance of new, very virulent H1N1 virus - antigenic shift
- 50 million deaths worldwide
- infected over half a billion
17
Q
Overview of swine flu
A
- H1N1
- rapid spread around globe 2009-10
- mild disease in most
- severe disease and death in significant number of people
18
Q
Future threats regarding influenza
A
- wild bird resevoir for influenza A - genetic diversity
- threat of emergence of new influenza A virus
19
Q
Criteria for establishment of a new influenza pandemic in humans
A
- a novel virus - with new haemagglutinin (HA) shape - antigenic shift
- association with disease
- susceptible population
- ability of virus to transmit from person to person
20
Q
Why do we need flu vaccines?
A
- to contain specific subtypes of influenza virus in circulation at that time
21
Q
What do the year’s flu vaccine contain?
A
- principal strains recovered during previous year
- usually one type B influenza and two type A influenza strains
