PRIS 2 > Pathogenesis 1 > Flashcards

Pathogenesis 1 Flashcards

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1
Q

What are viruses?

A
  • small parasite/particle/agents that are obligate intracellular parasites
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2
Q

Viruses are inert outside the host - what do they use the host for?

A
  • utilise the host cell processes to produce proteins and nucleic acid to reproduce
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3
Q

What does a virion consist of?

A
  • consists of nucleic acid and protein capsule
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4
Q

Which virus is most susceptible to spread and why?

A
  • RNA as there is lots of drift, they are segmented, not stable and there is massive spread
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5
Q

What is the capsid?
Where is it present?
What is it comprised of?

A
  • the protective layer surrounding the nucleic acid
  • present in both enveloped and naked viruses
  • composed of capsomeres (proteinaceous)
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6
Q

What are the 3 forms of symmetry?

A
  • icosahedral
  • helical
  • complex
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7
Q

How can you classify a virus?

A
  • nature of the genome
  • presence of an envelope
  • morphology
  • genome configuration
  • genome size
  • virion size
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8
Q

What is the gene arrangement like in DNA viruses and RNA viruses?

A
  • In DNA viruses all genes are om a single molecule
  • In RNA viruses genes are on different molecules (segmented)
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9
Q

Where do DNA viruses replicate?
Where do RNA viruses replicate?

A
  • DNA replication in the nucleus
  • RNA replication in the cytoplasm
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10
Q

What is the definition of pathogenesis?

A
  • the flow of the virus and the damage it causes
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11
Q

A successful virus doesn’t want to do what to the host?

A
  • doesn’t want to kill the host as the virus will die with it
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12
Q

Viral infection doesn’t mean disease - there is a spectrum - what is this?

A
  • exposure without infection
  • subclinical infection
  • mild disease
  • moderate disease
  • severe disease
  • death
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13
Q

What must a virus do to cause a disease?

A
  • must infect susceptible host
  • spread within the host
  • damage target tissues
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14
Q

What does virulence mean?

A
  • the measure of pathogenicity = capacity to cause disease
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15
Q

What is virulence unrelated to?

A
  • infectivity
  • transmissibility
    = contagiousness
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16
Q

What must happen for a virus to propagate?

A
  • must be shed
  • taken up by other susceptible hosts
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17
Q

What are host factors?

A
  • species
  • age, gender
  • immune status
  • nutritional status
  • co-infections
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18
Q

What are environmental factors?

A
  • climate/substrate
  • stocking/population density
  • management (feeding, health, vaccination)
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19
Q

What are virus factors?

A
  • strain (can change as virus is passed on)
  • replication/infective dose (how many viral particles are taken up)
  • rate of adaptation (immune evasion/infection/transmission)
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20
Q

What are the obligatory steps for viral infection?

A
  1. entry into host and primary virus replication = multiples locally
  2. local or general spread in the host (defined by cell and tissue tropism) with secondary virus replication
  3. shedding from host
  4. clearance from host
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21
Q

Describe what is happening when a virus has to enter a host:

A
  • evade hosts natural protective/cleansing mechanisms at a cellular level
  • the viruses takes over necessary host-cell functions for its own replications
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22
Q

What must the virus do for local or generalised spread in the host and what can happen to the host?

A
  • evade host defences (innate immune and inflammatory responses) and natural barriers to spread
  • damage to the host may occur at this time
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23
Q

When viruses shed from the host what do they need to ensure in order for it to be successful?

A
  • ensure they leave at a concentration needed to infect the next host
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24
Q

What is clearance from the host mediated by and is it always complete clearance?

A
  • adaptive immune responses mediate clearance
  • not always complete, viruses may persist and contribute to long-term shedding or chronic disease
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25
What does FMD have a tropism for?
- epithelial mucous membranes
26
Why do we need stamping out policies?
- because viruses can incubate and spread
27
What is an alternative to the stamping out policy?
- vaccination
28
To infect how must obligate intracellular viruses attach to infect cells?
- attach to integument - attach to mucosa
29
What is the integument like as a barrier?
- it has keratinised cells = difficult to penetrate unless broken
30
Mucosal surfaces are easier to penetrate where can these be found?
- GIT - Respiratory - Conjunctiva
31
Once a viruses has entered a host what can where can it infect?
- localisation at the site of entry or dissemination in host
32
Where are the routes of entry for the respiratory tract?
- mucosal surfaces (epithelial cells)
33
How can the respiratory tract defend against viruses?
- mucociliary blanket has a mucous layer which traps viruses and carries them out (such as coughing) - innate and adaptive immune mechanisms such as lymphoid aggregates (B-cells and T-cells)
34
What is primary viremia?
- initial stage of viral infection where virus enters the bloodstream from the first site of infection
35
How can viruses enter the GIT?
- ingestion of contaminated food/drink
36
What parts of the GIT are more resistant then the mucosal epithelium of the stomach and intestines?
- the oral cavity and oesophagus
37
What are the defences for the GIT?
- stomach acidity - mucous layer on mucosa - antimicrobial activity = digestive enzymes, bile secretions - innate and adaptive immunity especially defensins and IgA
38
Viruses targeting the GI system can be acid and bile resistant - give examples of these?
- rota virus - entero virus
39
What virus is liable to the defences of the GIT but is protected?
- TGE is liable but is protected in sucking piglet milk in stomach
40
What are the protective barriers of the skin?
- keratin = mechanical barrier - low pH - fatty acids in the skin - innate and adaptive immunity e.g., migratory dendritic cells
41
What can allow viruses to enter through the skin?
- deeper trauma (rupture) - generalised skin infection - insect bites - vertebrate bites
42
How can deep trauma get viruses past the skins barrier?
- introduces viruses into dermis/subcutis which can then go onto haematogenous dissemination
43
How can generalised skin infections such as LSD and sheep pox introduce viruses through the skin?
- usually due to systemic infection than localised cutaneous infection
44
What insects can introduce viruses? How do they get through the skin?
- culicoides , mosquitos, ticks - act like a needle and inject it in
45
What are the two ways insects can infect hosts with viruses?
- may be solely mechanical vectors = equine anaemia, fowl pox - if virus replicates in vector = biological vector - viruses transmitted by, and replicate in arthropod vectors = arboviruses , dengue, west Nile virus
46
What as example of a virus spread by vertebrate bites?
- rabies
47
What viruses are spread by venereal transmission?
- herpes - papillomavirus
48
What viruses can get in through the conjunctiva?
- adenoviruses - enteroviruses
49
What is a tropism?
- capacity of virus to infect specific cells in particular organ
50
For a tropism it requires interaction between what?
- requires interaction between viral attachment proteins and cell receptors
51
What are the receptors like for some viruses such as canine distemper?
- different receptors on different cells
52
How do receptors lead to tropisms?
- due to receptors for particular viruses being located in certain cell types and organs
53
What must a cell be like for a virus to successful take over?
- require cells to support viral entry and viral genome must be present with factors required for transcription and genome replication
54
What are the different mechanisms of spread?
- local spread - epithelial surfaces - sub-epithelial spread - lymphatic spread - spread via blood-stream - spread via nerves
55
How is local spread usually caused?
- usually by infecting neighbouring cells
56
What is local spread like in the skin - such as orf?
- confined to epidermis - local lesions
57
What is local spread like in the respiratory/GIT systems?
- extensive infection of mucosal epithelium - disease progresses rapidly - short incubation period
58
What is spread like for the influenza virus in mammals?
- restricted to epithelial surface (little sub-epithelial spread) - no receptors/cellular factors - extensive damage to lungs
59
If a virus is restricted to the epithelium is doesn't mean its low severity if its affecting the GIT mucosa what can this cause in neonates?
- often fatal diarrhoea
60
Some viruses breach the epithelial barrier and invade subepithelial tissues how do they do this?
- By targeted migration within phagocytic leukocytes especially dendritic cells and macrophages
61
How do dendritic cells respond to a virus?
- first appear as immature cells > survey for antigens > ingest > mature (= antigen presenting cells) > pass to lymph node > present antigen to T-lymphocytes > produce antibody
62
Where are dendritic cells abundant and what are they critical for?
- abundant in skin cells and all mucosal surfaces - critical in line of defence
63
How can viruses use dendritic cells for sub-epithelial invasion?
- viruses move via dendritic cells to lymphoid organs e.g., tonsils, lymph nodes, the may be inactive or may replicate in macrophages
64
Viruses that spread by dendritic cells are important in what viruses?
- bluetongue - AHS - HIV
65
Other than targeting migrating within phagocytic leukocytes what's another way viruses can invade sub-epithelially?
- directional shedding from epithelium into lumen of respiratory or GI tracts and leads to immediate shedding into environment
66
If viruses replicate in macrophages in lymph nodes how do they spread?
- spread via bloodstream throughout body, either within cells or as cell-free virions
67
What do disseminated infections often target?
- often target blood filtering organs such as lungs, liver and spleen
68
What is the most effective means of spread?
- spread via the bloodstream
69
Initial entry into the blood is called what?
- primary viraemia - usually subclinical
70
What viruses can be free in plasma?
- parvoviruses - enteroviruses - togaviruses
71
Viruses can be spread in the bloodstream and carried by cells - what cells are theses and why do they survive better this way than when free in plasma?
- mostly carried by lymphocytes and monocytes - survive better than when in plasma as they are protected from antibodies
72
What virus is carried by monocytes?
- canine distemper
73
What viruses are carried by lymphocytes?
- mareks disease - bovine leukosis
74
What viruses are carried by erythrocytes?
- ASF - BT
75
What viruses are carried by platelets?
- EIA - BVD
76
When may viruses spread by nerves occur?
- may occur after haematogenous spread or invasion of peripheral nerves
77
How can herpesvirus be spread via nerves?
- it can travel to CNS in axon cytoplasm
78
What nerves are involved in virus spread?
- sensory - motor - automimic * most viruses cross cell-cell junctions
79
What type of virus is more resistant in the environment than respiratory?
- enteric viruses = more resistant
80
Where are enteric viruses shed?
- in the faeces
81
How can viruses in the skin be shed?
- via direct contact
82
What are other ways that viruses can be shed?
- urine - semen - milk - slaughtered animals
PRIS 2
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