11.6 Viral Transmission and Pathogenesis Flashcards
Describe direct virus transmission. Through what can it occur?
- Occurs through direct body contact with tissues or fluids of infected individual
- Can occur through mucous membranes (e.g. eyes/mouth) and skin/wounds
Describe two mechanisms of indirect virus transmission
- Fomite transmission
- Vector mediated transmission (e.g. mosquitos)
Describe three kinds of transmissions of viruses between/within humans and other animals
- Enzootic (Within one animal species)
- Epizootic (between multiple animal species)
- Zoonotic (from animals to humans via any means)
Describe different modes of viral transmission across mucosal surfaces
- Respiratory (airborne)
- Enteric (oral)
- Sexual transmission
Describe different modes of viral transmission that involve skin penetration
- Bloodborne
- Vector-borne
- Cuts, scrapes, bites, needles
What is viraemia?
Virus existing in blood
What does it mean that viruses are obligate intracelllular parasites?
They must enter a host cell in order to replicate
What is the only situation in which the genome of a virus can serve its function?
Inside a living cell
What are four important aspects of viral pathogenesis?
- Transmission
- Viral Replication (effect on infected cells?)
- Spread within the body (areas?)
- Evasion of host defense systems
Transient vs persistent infection
Transient: successful clearance
Persistent: unsuccessful clearance
What is a single viral particle called?
Virion
List five possible effects of viral infection at the cellular level
- Cytopathic effect (cell death/cytoskeletal changes)
- Giant cell formation
- Malignant transformation
- Inclusion bodies
- No change
What is the opposite of a localised infection?
Systemic infection
What factors can influence the effectiveness of an antiviral immune response?
- Rate of virus replication & antigen presentation
- Size of dose of virus
- Route of infection/host age
- Ability of virus to evade the immune system
Which two concepts underlie the clinical presentation of viral infection?
- Effects of viral replication on host
- Symptoms caused by the antiviral immune response itself
What are the four classifications of viral infections in terms of permutations?
- Transient localised
- Transient systemic
- Persistent localised
- Persistent systemic
List five different regions in which infection can occur
- Respiratory tract
- Gastrointestinal tract
- Liver
- Nervous system
- Skin
Give an example of a viral respiratory infection
Influenza
Give an example of a viral GI infection
Gastroenteritis
Give an example of a viral Liver infection
Hep A/B/C
Give an example of a viral nervous infection
Encephalitis
Give an example of a viral skin infection
Chickenpox
Effect of tumour necrosis factor alpha
- Promotes systemic inflammation
- Inflammatory chemokines production and leukocyte recruitment
Effect of interleukin 1 beta
- Mediates inflammatory response
- Promotes inflammatory chemokine response and leukocyte recruitment
Effects of type 1 interferon
- Induces cellular resistance to viral infection
- Inhibits viral replication/dissemination
What are PAMPs?
Pathogen associated molecular patterns
What are DAMPs?
Damage associated molecular patterns
What receptors detect viral infection in the innate immune system?
Pattern recognition receptors
Which antigen presenting cells in the innate immune response detect viral infection?
- Dendritic cells
- Macrophages
What can PRRs detect?
PAMPs and DAMPs
What are the two types of PRRs?
- Cytosolic receptors
- Toll-like receptors
What do cytosolic recptors detect?
DNA and RNA in the cell
Where are cytosolic receptors present?
In the cytoplasm
How can nucleic acid be a PAMP if our own cells have DNA and RNA?
- Viral RNAs lack the methyl cap on the 5’ end, which our own cells have. Therefore, such RNA is detected as a PAMP, and an immune response is mounted.
- Presence of dsRNA in cytoplasm due to genomic replication (doesn’t usually occur)
- Presence of dsDNA in cytoplasm
Where are TLRs located? How does this influence the importance of various cells?
- Located in endosome
- Makes the role of phagocytes very important, as these form endosomes
What does TLR3 detect?
dsRNA
What do TLR7/8 detect?
ssRNA
What do TLR9 detect?
Unmethylated CpG-DNA
What does “pyrogenic” mean?
Causing fever
What are the three outcomes of interferon type 1?
- mRNA degradation
- Inhibition of transcription
- Inhibition of translation
What are some common clinical symptoms of viral infection, and what causes them?
- Fever
- Tiredness
- Muscle ache
Caused by host antiviral response
