Respiratory Viruses - Influenza, RSV, Parainfluenza, hMPV Flashcards
What are the two main types of viruses?
DNA viruses
RNA viruses
What are some differences between RNA and DNA viuses?
RNA viruses replicate in the cytoplasm ,use RNA-dependent RNA polymerase
DNA viruses in the nucleus, uses host DNA replication machinery
RNA has a high mutation rate while DNA has a lower mutation rate as it has proofreading mechanisms
RNA undergoes rapid evolution and is less stable, DNA has a more consistent genome and is more stable
RNA only cause acute infections while DNA cause both acute and latent (think chickenpox)
Why do only DNA viruses cause latent infection?
RNA viruses tend to mutate quickly meaning you can repeatedly get RNA viruses but you never get the same one e.g. flu
DNA viruses dont mutate and have more stable genomes so you build immunity against them such as chickenpox
Give some examples of RNA viruse
Orthomyxoviridae -> influenza A, B, C
Paramyxoviridae -> Parainfluenza, RSV
Picornaviridae -> Rhinoviurs, Coxsackie virus, Enterovirus (echovirus), Parechovirus
Coronaviridae -> coronavirus, SARS CoV, MERS
Bunyaviridae -> hantavirus
What kind of infection does coxsackie A cause?
Hand foot and mouth
-> similar to chickenpox
Everyone has had this at some point -> its highly contagious and spreads rapidly in playschools etc
Give an example of a DNA virus
Adenovirus
When do we usually ID enterovirus in the lab?
Usually flags for meningitis
Usually the most common flag on the film array in the lab
What are othomyxoviridae, what viruses are in this family?
(4)
A family of RNA viruses primarily known for causing influenza, Influenza A, B, C and D
Characterised by their segmented, single stranded RNA genomes and unique surface proteins: Hemagglutinin and neuraminidase
They exhibit a remarkable ability to mutate and re-assort, this contributes to their virulence and emergence of new strains
Constatly pose ongoing challenges for public health, continuous surveillance and vaccine development to mitigate impact and control influenza outbreaks
What influenza strains are we concerned with?
A = most common strain, causes seasonal epidemics(not flu), can infect multiple different species such as birds and pigs
B = only affects humans, seasonal flu
C = causes mild illness, not much diagnostics done on this as it usually goes away on its own
D = doesnt infect humans so we dont care
What are the different components of an orthomyxoviridae?
Shape = spherical or filamentous
Size = 80-120 nm in diameter
Envelope = lipid bilayer derived from the host cell
Surface proteins:
- Hemagglutinin (HA)
- Neuraminidase (NA)
Nucleocapsid:
- Segmented RNA genome, 8 RNA segments encoding viral proteins
- Nucleoprotein (NP) encases the RNa forming a helical structure
Matrix proteins: M1 and M2
What does Haemagglutinin do, why is it significant?
HA binds to host cell receptors: key vaccine target
What does neuramidase do?
It facilitates the release of new vira particles
What makes up an RNA nucleocapsid?
A segmented RNA genome composed of eight RNA segment whic encode viral proteins
Surrounded by a nucleoprotein, forming a helical structure
What matix proteins are found in orthomyxoviridae, what do they do?
M1 proteins which maintain viral stucture and aid assembly
M2 proteins which facilitate viral uncoating in host cells
What are the structural components of influenzae
Lipid envelope
Surface glycoproteins: HA and NA
What are the structural components of influenzae
Lipid envelope
Surface glycoproteins: HA and NA
Talk about the lipid envelope of influenza
It has a protective outer layer made of lipids (fats) that encase the virus
Talk about the haemagglutinin of Influenza, how many on cell, what is the function
Approximately 500 spikes per virus particles
HA binds to receptors on host cells, allowing the virus to enter and initiate infection by fusing its envelope with the host cell’s plasma membrane
Allows virus to attach to and enter host cells
Talk about the neuraminidase of Influenza, how many on cell, what is the function
There are 100 spikes per virus particle
This helps release new virus particles from the surface of infected cells so that they can go on to infect other cells
How do we make use of HA and NA combinations?
(2)
We use specific combinations of these proteins to determine the subtype of the influenza virus e.g. H1N1 = swine flu
HA and NA are targetted by our immune system
How can influenza use HA and NA to evade our immune system?
(4)
Influenza can change its HA protein through mutations or genetic reassortent
This allows influenza to evade detection by the immune system
This variation can lead to new strains that the immune system may not recognise thus making it harder for the body to fight -> have to produce new antibodies now etc
The same concept applies to vaccines -> new vaccines needed yearly
What is an antigen found on group A, B and C influenza?
Internal ribonucleoprotein (RNP)
How do we name viruses, according to WHO
Virus type, geographic origin, strain number, year of isolation, virus subtype
Virus subtype (H3N2)
Talk about antigenic variability in influenza viruses, why does it happen and what is it?
(3)
Influenza is RNA based so they are dynamic and are continuously evolving
Antigenic variability refers to the ability of these viruses to change their surface proteins, HA and NA
This happens due to either antigenic drift or shift
What is the definition of antigenic drift?
A gradual process where minor mutations occur in the genes encoding HA and NA over time
What are the results of an antigenic drift?
Mutations alter the structure of the proteins, leading to changes in the virus’s antigens
As a result, the immune system may not recognize the virus, even if a person has been previously infected or vaccinated against an earlier strain
What are the impact of antigenic drift?
Antigenic drift is responsible for seasonal influenza epidemics and the need for annual updates to flu vaccines
What is the definition of antigenic shift?
this is a more dramatic change that occurs when two different strains of influenza viruses infectt the same host cell and exchange genetic material
2+ viruses that come together
What is the result of an antigenic shift?
This reassortment can lead to the emergence of a new influenza subtype with a novel combination of HA and NA proteins
This new strain may be significantly different from previous strains
This is how pandemics ocur as nobody has immunity
May confer increased pathogenicity and/or change the ability to spread rapidly from person to peron
When does shift usually occur
(2)
Usually occurs in pigs
This is because pigs can bi infected by both birds or humans
What is the impact of antigenic shift?
Leads to pandemics as the population mayhave little to no pre-existing immunity against the newly formed virus
Who does influenza A infect, why is this significant?
(3)
A subtype of the influenza virus that primarilyinfects humans and other animal species, including birds and pigs
Influenza A is known to cause antigenic drift and shift every 40 years, leads to seasonal epidemics and pandemics
Vaccination and antiviral treatments are crucial for prevention and management
What are the symptoms of Influenza A?
Fever, cough, sore throat, body aches, fatigue
Sever illness in vulnerable populations
Comment on the serotype of influenza A
There are 18 HA subtypes and 11 NA subtypes leading to a possible 198 possible HA and NA combinations
However only 3 subtypes, all derived from swine can infect and transmit among humans (H1N1, H1N2 and H3N2)
Comment on the trends of influenza A and B
A tends to predominate
B only most common in 2017-2018 and this was due to poor vaccination cover
B coverage went back up with 99% of cases being A in 2018-2019
Comment on the trend in influenza serotypes
Comment on the trend in influenza A serotypes (2017-2024)
The specific A serotype that is prevalent tends to vary year on year
In 2017-2018 H1N1 and H3N2 showed similar numbers
In 2018-2019 H1N1 prevailed over H3N2
In 2022-2023 H1N1 accounted for 91% and H3N2 for 9%
In 2023-2024 H3N2 prevailed
Why does prevalent influenza serotypes change year on year?
Its all down to coverage by the flu vaccine
Some years we do a better job at predicting strains then others
What are the two ways antigenic drift occurs?
Genetic reassortment
Change of species specificity
How can genetic reassortment cause antigenic drift?
Viruses from different species such as avian and swine viruses infect the same host and mix with human influenza viruses
This resulting hybrid virus can have new combinations of haemagglutinin (HA) and neuramidase (NA) proteins
How can a change of species specificity result in antigenic drift?
The reassorted virus can gain the ability to infect humans directly from animals, particularly from poultry, which is a common source of zoonotic transmission
How can antigenic drift cause a pandemic
(4)
New subtype means no protection from old vaccines
Little or no immunity to a novel virus, virus is efficently transmitted among humans -> no heard immunity
Pandemic can result in widespread morbidity and mortality worldwide
A good example is the 2009 H1N1 virus swsine flu
How can antigenic drift cause a pandemic
(4)
New subtype means no protection from old vaccines
Little or no immunity to a novel virus, virus is efficently transmitted among humans -> no heard immunity
Pandemic can result in widespread morbidity and mortality worldwide
A good example is the 2009 H1N1 virus swsine flu