Lec 4: Transmission Flashcards

1
Q

if the virus does not produce enough visions it will

A

die out

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2
Q

another possibility for viral survival…

which are…

A

to be maintained in cells as nucleic acids

which are replicated and passed on to daughter cells when they divide

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3
Q

Viruses of bacteria and other microbial hosts are…

A

…released from infected cells into the environment

- dependent upon chance encounters with susceptible cells.

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4
Q

Viruses of multicellular animals and plants — may…

A

…spread to adjacent cells, or to cells in a distant part of the host.

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5
Q

Some virus infections modify the…

& ex:

A

…behaviour of their hosts in order to increase the probability of transmission.
& ex: Mammals infected with rabies virus often become aggressive or rabid.

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6
Q

some viruses can be transmitted to new hosts without…

A

…seeing the light of day , (without exposure to the outside environment) — transmitted by kissing, sex, birth, vectors, etc.

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7
Q

Classical route of journey between hosts:

A

Cell free virions bind to permissive host cell with receptor-ligand interactions, followed by fusion to enter the cytoplasm and then replicative events.

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8
Q

Cell to cell transmission:

A

An actively infected cell can directly infect a second cell, without requirement for releasing cell-free virions into the local environment.

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9
Q

Why is cell to cell transmission advantageous? (2)

A
  • Bypasses the need for virus diffusion into the local enviroment.
  • Minimizes exposure to harsh environment, and viral neutralization defenses such as antibodies and complement.
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10
Q

some viruses travel ____ _________, through: (3)

A

long distances, through:

  1. ) bird migration
  2. ) human travel
  3. ) animal export
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11
Q

In a multicellular organism, viruses must survive…

In theory,…

A

…host defense mechanisms before suitable host cells are encountered.
…a single virion can initiate an infection, but in practice a host must be inoculated with a minimum number of virions in order for that host to become infected.

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12
Q

most vectors are

and sometimes referred to as

A

arthropods

“arboviruses”

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13
Q

Some viruses replicate in…

- There are viruses that can…

A

…one or more tissues and organs of their vectors.

- …replicate in both invertebrates and plants, and viruses that can replicate in both invertebrates and vertebrates.

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14
Q

Many (but not all) of the invertebrates suffer…

A

little or no harm when they are infected.

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15
Q

It’s possible that many of the modern plant viruses and vertebrate viruses are descended from…

A

…viruses of invertebrates that later extended their host ranges to plants or vertebrates.

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16
Q

high degree of specificity between…

A

most vectors and the viruses that they transmit

17
Q

Plant cells have thick cell walls =

tf most viruses are carried…

A

significant barriers to virus entry.

…across these barriers by vectors

18
Q

Some plant virus-vector specificity depends on…

A

specific amino acid sequences in capsid proteins.

19
Q

Some plant-parasitic fungi can also act as

A

virus vectors.

20
Q

~20% of plant viruses can be

many can be transmitted by…

A

vertically via seeds

…artificial means (ex: grafting)

21
Q

Transmission of vertebrate viruses: (3)

A
  • Non-vector transmission of vertebrate viruses
  • Vector transmission of vertebrate viruses
  • Virus survival in the vertebrate host
22
Q

(Non-vector transmission of vertebrate viruses) can happen via: (3)

A
  • via mucous membranes of upper respiratory tract, (e.g. flu virus)
  • Release from lesions and by direct contact, (e.g. foot and mouth disease virus, herpes simplex virus (lips))
  • Some infections (e.g. common cold, rotavirus) remain limited to these tissues, while others (e.g. measles, polio, HIV) cross the epithelial surface and spread to other organs and tissues.
23
Q

(Vector transmission of vertebrate viruses) can happen via: (2)

A
  • Mainly blood-feeding arthropods that acquire their viruses when they take blood meals from infected animals.
  • Transmitted during medical procedures by inanimate vectors (needles)
24
Q

(Virus survival in the vertebrate host)
Viruses must…

& ex.’s:

A

…evade several defense systems

  • removal by the mucociliary escalator in airways.
  • Inactivation by extremes of pH in the gastro-intestinal tract .
  • The surfaces fluids of respiratory, intestinal and urinogenital tracts which contain antiviral substances.
  • The antiviral substances such as complement proteins, which can undergo modifications and damage enveloped virions by insertion into their membranes.
  • Viruses may be phagocytosed by a range of cells such as macrophages.
  • Antibodies
  • Vaccines
25
Q

(Transmission of INVERTEBRATE viruses)
• Invertebrates are hosts…
• Many of these viruses have evolved…

A
  • …to many other viruses that replicate only in invertebrates.
  • …occlusion bodies, (large protein structures in which virions become embedded in the infected cell)
26
Q

(Transmission of INVERTEBRATE viruses)

Putrefaction of insects that have been killed by virus infection results in…

A

…the deposit of occlusion bodies on leaves. Occlusion bodies ingested by insects are dissolved in the midgut, releasing virions.

27
Q

Permissive cells support…,

- leading to…

A

…complete DNA and protein synthesis,

- …the production of infectious progeny and lysis of the host cell.

28
Q

Semipermissive cells support…

A

limited viral replication.

29
Q

Nonpermissive cells survive…

A

…viral challenge because if the virus enters the host, viral replication does not occur.

30
Q

Permissive cells must have…

A

…appropriate receptors that the virus can bind to.

Must be inducible; cell proteins, such as transcription factors and enzymes.

31
Q

(Permissive cells)

Some viruses of eukaryotes need…

A

…the host cell to be in a particular phase of the cell cycle

32
Q

Permissive cells must lack…

A

…defenses against the virus, or the virus must have the ability to overcome the defences of the cell.