Viral pathogenesis

Question 1

What are the 4 epidemiological patterns of viral infections?

Answer 1

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

Question 2

What are the distinguishing characteristics of viruses

Answer 2

Obligate intracellular parasites

• contain DNA/RNA genomes => structural, functional proteins
• assembled using host cell proteins

Question 3

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

Answer 3

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

Question 4

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

Answer 4

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+

Question 5

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

Answer 5

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-

Question 6

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

Answer 6

Flaviviridae (HepC, Yellow fever=hepatitis)(Dengue, West Nile)

• enveloped
• ss+

Filoviridae (ebola, Marburg)

• enveloped
• ss-

Question 7

What is the function of the capsid

Answer 7

Made up from a small no of virally encoded protein subunits => capsomeres

Nucleocapsid => viral genome enclosed by capsid protein coat

Protects genetic material

Question 8

What is the function of the viral envelope

-how do the characteristics of the virus change

Answer 8

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

Question 9

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

Answer 9

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

Question 10

Describe how different viruses undergo gene expression and replication

• DNA (large and small)
• RNA
• retroviruses

Answer 10

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

Question 11

What are the 4 key steps in viral infection

Answer 11

Entry and spread into body

Evasion of hosts immune system

Multiplication

Transmission from body into new host

Question 12

What are the most common nosocomial viral infections

Why do they happen

Answer 12

Infection easily transmitted by staff, patients, visitors. 
Cannot always be prevented by proper hand washing
-RSV
-noro
-flu
-chickenpox
-measles
-COVID19

Question 13

What is immunopathogenesis

-what are the 4 mechanisms

Answer 13

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

Question 14

What is the difference between pathogenicity and virulence

-how can virulence be measured

Answer 14

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

Question 15

What are viral virulence factors

-what are the 4 ways they can cause disease

Answer 15

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

Question 16

What are superantigens

Answer 16

Toxins that stimulate the immune system

-bind directly to MHCII non specifically => stimulate large no of T cells