Virology Flashcards
Name 3 routes of pathogen entry
Respiratory tract, skin, urogenital tract (also conjunctiva and mouth)
What are 3 barriers of the GI tract against viral infection
pH 2, proteases and mucus (also bile salts)
Name 3 viruses that infect GI epithelial cells after bypassing host defense mechanisms
Rotavirus, parvovirus and adenovirus
What are 3 barriers of the respiratory tract against viral infection
Mucous, ciliated epithelia and secreted IgA
What happens to airborne droplets smaller than 5um
They remain airborne for long periods
What happens to airborne droplets larger than 5um
They are subject to gravity and get caught in nasal turbinates
Define viremia
The presence of virus in the blood after they bypass the lymphatics
Name 2 cell types virions can encounter in the blood
Cells of the reticuloendothelial system and vascular endothelial cells
Describe 3 outcomes of virions interacting with reticuloendothelial cells
- Virus is phagocytosed and presented to the immune system
- Virus resists phagocytosis and there is prolonged viremia
- Virus replicates after being phagocytosed and causes an increased secondary viremia
At what point/where can viral particles infect vascular endothelial cells
If they are localized in the endothelial cells of capillaries and venules at the point where the vascular endothelial barrier is the thinnest
What is intra-axonal spread
When a virus enters sensory and motor neurons and travels through them to the CNS
What is a virus, and what makes it different from a bacteria?
A small obligate intracellular parasite
The largest viral genome is smaller than the smallest bacterial genome
Capsid + genome =
Nucleocapsid
Influenza: genome, enveloped/non-enveloped
-ssRNA segmented genome
Enveloped
Rinderpest: genome, enveloped/non-enveloped
-ssRNA non-segmented genome
Enveloped
Coronavirus: genome, enveloped/non-enveloped
+ssRNA non-segmented genome
Enveloped
What is the smallest virus known to infect birds/mammals and what are its features
Porcine circovirus
ssDNA genome (3 genes), non-enveloped
What are anti-receptors on the virus particle called?
Virus attachment protein
Define an attachment factor
It doesn’t cause a conformational change in an anti-receptor
Speaking broadly, which types of viruses use endocytosis for cell entry
All non-enveloped and some enveloped (flu)
Nucleic acid is always read…
3’ to 5’
Nucleic acid is always synthesized…
5’ to 3’
What are the 7 classes of viruses
dsDNA, ssDNA, dsRNA, +ssRNA, -ssRNA, retroviridae, reversiviruses
What causes virus-induced cell lysis
Viroporins
What are the 3 things required for virus budding
- One or more viral membrane proteins
- One or more viral matrix proteins
- The viral genome
What do viruses use to help with membrane fission
The cell ESCRT pathway
List 5 viral spread mechanisms
- Exit then re-entry
- Fusion of PM of infected and uninfected cells
- Virus surfing (stays bound to cell membrane)
- Induced migration of infected cell
- Actin “comet” formation
Define cytopathic effect
Any cell abnormality induced by virus infection
How do viruses cause CPE?
Shutdown host protein synthesis (cap snatching in influenza virus), apoptosis, permeability changes
Define inclusion body
Non-membrane bound organelle comprised of virus components
Define syncytium
Cell surface fusion of multiple cells to an infected cell
How do you detect viral genome for DNA viruses vs RNA viruses
PCR for DNA
RT-PCR for RNA
How do you quantify virus infectivity
Assay CPE from titrated samples
Which cell types/effectors are seen most immediately after infection with a virus
IFN a/b (type I IFN) and NK cells
What are 2 type I IFNs
Alpha and beta
What is a type II IFN
Gamma
Are IFNs virus specific?
No
What is the role of IFNs
They react with uninfected cells to make them resistant to infection from other viruses
What are the main producers of IFN alpha
Macrophages
What are the main producers of IFN beta
Fibroblasts
Which viral genome is best at inducing IFNs
RNA viruses
What do macrophages produce to prevent viral infection
IFN-alpha, TNF-alpha and IL-12
What do NK cells majorly produce
IFN-gamma (also TNF-alpha)
Which cells do NK cells recognize
Those which have down regulated MHCI expression and those which have IgG attached
List 3 ways antibodies can neutralize virus infectivity
- Block attachment to a receptor
- block virus fusion and entry
- block uncoating of virus
How does the innate immune response contribute to immune-mediated viral disease
IFN/inflammatory response can cause minor symptoms
Cytokine storm
How does the cell-mediated immune response contribute to immune-mediated viral disease
Cell-mediated immunity contributes to cellular infiltrates and oedema, and in cases where this does not stop once the pathogen is cleared it will cause issues
What are poxvirus virulence genes mainly linked to
To subverting host defenses - not necessarily essential for replication
Which Sialic acid linkage does avian influenza target?
alpha 2,3
Name 3 genetic basis’s for host resistance to viral infection
- host range variation
- variation in innate genes
- variation in host genes needed for replication
What host gene is involved in resistance to influenza
Mx gene
What is different about low and high pathogenic influenza
High pathogenic strains are able to have HA cleaved by ubiquitous proteases, whereas low pathogenic HA can only be cleaved by a few
Where are Ag/Ab complexes likely to localize in cases where they are present in excess
Kidney glomeruli, brain, spleen, lymph nodes
Virus persistence in the population is ___ from persistence in the host
Independent
R0 is defined as….
The average number of new cases arising from one infection in a totally susceptible population
Which influenza species majorly affects animals and humans
Influenza A
Explain the basis of antigenic drift in influenza
The viral RdRp is very error prone which means there can be a lot of small mutations, this creates sequence variations in HA and NA and makes a strain you were previously infected with pathogenic again
Describe the influenza genome and how it contributes to antigenic drift/shift
It is a -ssRNA genome that requires and RdRp (antigenic drift) and is segmented (antigenic shift)
How is measles virus persistent
It relies on new susceptible hosts
How does EIAV persist
Antigenic variation within the initial infecting population creates new populations to which the host does not have an immune response to
List 3 forms of immune evasion
- antigenic variation
- hiding (immune privileged site, latency)
- immunosuppression
What is an immune privileged site
Regions in the body that are naturally less subject to immune responses than other areas
What are the two disease syndromes cause by BVDV
BVD and mucosal disease
When does a calf need to be infected with BVDV for persistent infection to develop
Between 80-125 days in utero
When can mucosal disease develop in BVDV
When the non-cytopathic type mutates to cytopathic or the animal is exposed to cytopathic biotype in persistently infected animals
What are some stimuli known to reactivate herpesvirus
U.V light, immunosuppression or general stress to the body
