Lecture 16 - Flu Flashcards
(52 cards)
Influenza viruses are members of what virus family?
Orthomyxovirus family
Identify Influenza virus characteristics
- Envelope or No envelope
- Genetic material
- Required enzyme
- Envelope
- (-)ssRNA
- RNA-dependent RNA-polymerases
What must Influenza bring with it for replication of its genetic material to occur?
RNA-dependent RNA-polymerase to provide mRNA for protein production and to replicate the RNA genome
T or F, Influenza virus has a segmented, (-)ssRNA genome which does not have the ability to mutate frequently
False, It does have the ability to mutate frequently
What is significant about the influenza viral genome other than being (-)ssRNA
It is segmented, being found in 8 different pieces associated with 8 separate nucleocapsids within each viral particle.
What does influenza’s segmented genome allow it to do?
It allows for genome mixing when two different influenza strains infect the same cell.
What are the two important spike proteins that are the main target of the adaptive immune response
Neuraminidase (N protein)
Hemagglutinin (H protein)
What happens if N protein and H protein get switched?
Antigenic shift. A virus with a brand new combination of spikes goes on to cause disease as a new strain
What is a pandemic?
Worldwide epidemics
Other than antigenic shift, how else can two spike protein genes be switched?
By a simple mistake during viral genome replication. Such minor point mutations can result in a new amino acid near region of spike protein that interacts with Ab
How does the host immune system respond to influenza viruses?
Antibody immunity to influenza viruses usually involves Abs binding and covering the key spike epitopes, blocking virus spike binding to the host cell and thus neutralizing the virus
What is Antigenic drift and how do viruses avoid the immune system of the host?
Antigenic drift is when a minor point mutation results in a new amino acid at or near the epitope of spike proteins that interact with antibodies. When this epitope is altered, it can prevent antibody from binding but still allow the virus to infect. Subsequent hosts are no longer immune to this new mutant and a new epidemic is on its way!
Make sure to understand the difference between Antigenic Shift and Antigenic Drift
Shift - Proteins are switched during genome mixing of two different influenza strains infect the same cell.
Drift - A viral point mutation occurs at a spike site, disallowing the antibody to bind and neutralize the virus
What is a common feature of viruses that use RNA-dependent RNA-polymerases?
Antigenic drift because of the lack to spell-check which is a feature of DNA-dependent polymerases
When was the last worldwide pandemic and what was it?
Swine Flu (H1N1) in 2009 emerged in Mexico
What occurs in the nucleus of the cell in Influenza that is unique among human RNA viruses (except retro viruses)
It replicates in the nucleus of the cell.
For antigenic shift to occur, what is required?
Normally requires that the viruses have a segmented genome and more than one host species
Hemagglutinin (H protein) has what specific function?
Facilitates viral attachment and fusion with the cell membrane
Nuraminidase (N protein) has what specific function?
helps viral release by cleaving neuraminic acid on the cell surface
Drift mutations can lead to what? Shift mutations can lead to what?
Drift mutations: Epidemics
Shift mutations: Pandemics
What can be done to determine and diagnose if an influenza virus is the cause of infection?
Influenza viruses agglutinate RBCs. A key technique is based on the fact that influenza viruses can grow in eggs and that they bind sialic acids, which are found on some RBC
How do we determine if a patient has developed neutralizing antibodies to a certain influenza strain?
Hemagglutination Inhibition Assay. Antibodies to spikes of each viral strain can block the RBC agglutination by neutralizing just like they do in vivo. If the antibody is present, RBCs will not agglutinate
What is the innate immunity that hosts use against viral infections?
Interferons (IFN-alpha and IFN-beta) that are pro-inflammatory and inhibit viral replication “hold the fort” until influenza specific lymphocytes can clone
Describe the process when Specific immune system kicks in responding to the influenza virus that replicates too fast or host immunity is inadequate
- Ab neutralizes the free viruses and Tc cells destroy infected cells (viral factories)
- Unfortunately, Tc cell killing can leave lung epithelial cells significantly denuded and susceptible to inhaled normal bacterial flora
