Viral pathogenesis Flashcards
What are the 4 epidemiological patterns of viral infections?
Sporadic => occasional disease only
Endemic => disease constantly present in a community, population
Epidemic => disease has a greater no of cases than normal in an area within a short period of time
Pandemic => epidemic worldwide
What are the distinguishing characteristics of viruses
Obligate intracellular parasites
- contain DNA/RNA genomes => structural, functional proteins
- assembled using host cell proteins
What are the 6 families of DNA viruses
- which have an envelope
- what is their symmetry
- what type of genome do they have
- what are some important examples and their presentation
Parvoviridae (Erythrovirus B19, rash)
- naked
- icosahedral
- ss
Papovaviridae (HPV, polyomas)
- naked
- icosahedral
- ds
Adenoviridae (adenoviruses, resp/GI transmission/symptoms)
- naked
- icosahedral
- ds
Hepadnaviridae (HepB, hepatitis)
- envelope
- icosahedral
- ds
Herpesviridae (HSV, VZV, EBV, rash)
- envelope
- icosahedral
- ds
Poxviridae (smallpox)
- envelope
- complex
- ds
What are the names of the icosahedral RNA virus families
- do they have an envelope
- what type of genome do they have
- what are some important examples and their presentations
Reoviridae (rota=GI)
- naked
- ds segmented
Picornaviridae (entero=resp/GI symptoms/transmission)(rhino=resp)(HepA=hepatitis)
- naked
- ss+
Caliciviridae (noro=GI)
- naked
- ss+
Togaviridae (rubella=rash)(chikungunya)
- enveloped
- ss+
What are the names of the 6 helical RNA virus families
- do they have an envelope
- what type of genome do they have
- what are some important examples and their presentations
Coronaviridae (seasonal, MERS, SARS, COV1, 2=resp/GI symptoms/transmission)
- enveloped
- ss+
Rhabdoviridae (rabies)
- enveloped
- ss+
Orthomyxoviridae (flu=resp)
- enveloped
- ss- segmented
Arenaviridae (lassa)
- enveloped
- ss- segmented
Paramyxoviridae (measles=rash)(mumps)(paraflu, RSV=resp)
- enveloped
- ss-
Bunyaviridae (hantavirus, Crimean-Congo)
- enveloped
- ss-
What are the names of the 2 complex/mystery RNA virus families
- do they have an envelope
- what type of genome do they have
- what are some important examples an their presentations
Flaviviridae (HepC, Yellow fever=hepatitis)(Dengue, West Nile)
- enveloped
- ss+
Filoviridae (ebola, Marburg)
- enveloped
- ss-
What is the function of the capsid
Made up from a small no of virally encoded protein subunits => capsomeres
Nucleocapsid => viral genome enclosed by capsid protein coat
Protects genetic material
What is the function of the viral envelope
-how do the characteristics of the virus change
Lipid bilayer => derived from host cell membranes
Naked => stable in environment, can be transmitted by food, water
Enveloped => cannot persist in environment
Less immunogenic
- phospholipid bilayer appears as host cells
- glycosylated proteins => AGs less exposed
- can bud from host cells without killing it
- increases tolerance to mutations in nucleocapsid
What is the function of viral surface proteins
- what is a tropism
- what makes a cell permissive
How can this be exploited by the immune system
Attach to specific ligands on surface of host cell
Tropism => tissues within a given host that are infected by the pathogen
Permissive cells => allows for pathogen replication
Also targets for AB in neutralisation
Describe how different viruses undergo gene expression and replication
- DNA (large and small)
- RNA
- retroviruses
DNA, large => have own DNA dependent RNA polymerase
DNA, small => use host cell enzymes
RNA => encode own RNA dependent RNA polymerase with complementary RNA as template
-lack proofreading mech => error prone replication
Retroviruses and hepadna => reverse transcriptase
What are the 4 key steps in viral infection
Entry and spread into body
Evasion of hosts immune system
Multiplication
Transmission from body into new host
What are the most common nosocomial viral infections
Why do they happen
Infection easily transmitted by staff, patients, visitors. Cannot always be prevented by proper hand washing -RSV -noro -flu -chickenpox -measles -COVID19
What is immunopathogenesis
-what are the 4 mechanisms
Main cause of cell death in infections due to killing of infected cells by immune system
- innate, TLR response
- CD8 attack
- AB damage to host
- AB mediated complement fixing
What is the difference between pathogenicity and virulence
-how can virulence be measured
Pathogenicity => ability of microbe to cause disease
Virulence => degree of pathogenicity in a microbe
LD50 => no of pathogens that will kill 50% of hosts
ID50 => no of pathogens that will infect 50% of hosts
What are viral virulence factors
-what are the 4 ways they can cause disease
Genes that give the virus an advantage
- alter replication ability
- modify host defences (infected cell secretes viral proteins that mimic cytokines)
- enable spread in host
- act as toxic proteins
