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Microbiology > Evolution and emergence of new viruses > Flashcards

Evolution and emergence of new viruses Flashcards

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Biology 101 flashcards
1
Q

Virus evolution

A

viral polymerases make a lot of errors, so each copy of genome may contain errors and be different to others

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2
Q

Quasispecies

A

virus doesn’t exist in host as constant, homogenous species, and drug/environmental effects will exert selective pressures to influence alleles present

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3
Q

When may viruses face a bottleneck?

A

At transmission or during replication under limiting conditions
Those with advantageous mutations survive

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4
Q

Antiviral drug resistance

A

High mutation rate, large progeny numbers and short replication time make viral evolution in response to selective pressure very fast.

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5
Q

How does Anti Retroviral Therapy avoid resistance?

A

ART targets many HIV genes at many different points in replication cycle.
>1 drug targeting each point with different approach, so mutation doesn’t effect efficacy of all drugs

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6
Q

Why should a patient not be treated with a single drug?

A

Resistance is more likely to develop

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7
Q

Why is combination therapy essential?

E.g. HAART for HIV

A

As long as there’s drugs that target different genes in virus, if 1 virus gets a resistant mutation in 1 place, it is still susceptible to drugs targeting other genes.

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8
Q

Antibody selective pressure applied by neutralising antibodies

A

Can prevent viruses entering cells

But also select for those in the quasispecies that have antigen mutations unsusceptible to antibodies

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9
Q

Antigenic drift

A

gradual evolution of virus driven by antibody selective pressure

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10
Q

What does antigenic drift necessitate?

A

Yearly update to vaccine

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11
Q

What does antigenic drift allow?

A

Re-emergence of virus

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12
Q

Zoonosis

A

Virus emerges from animals, crosses into humans

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13
Q

Example of zoonotic virus

A

Ebola

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14
Q

How do new viruses emerge?

A 
Zoonosis
Genetic variation (Antigenic drift)
Increased exposure- travel or world population
Increased exposure- spread of vector
New discoveries
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15
Q

Host range

A

Range of cells that can act as a host to a virus or bacteriophage

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16
Q

Examples of ‘New’ viruses that have only recently been discovered or detected

A

‘Non A non B’ hepatitis caused by hepatitis C virus
HPV 16 and 18 as cause of cervical cancer
HHV8 as cause of Kaposi’s Sarcoma noticed during AIDS pandemic
Merkel cell polyoma virus identified in tumours as non-human sequence

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17
Q

Global influences on emerging infections

A 
Environmental modification
World population
Climate change
Travel
Farming practises; monocultures
Immunosuppressed humans
Medical progress
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18
Q

Arboviruses

A

Transmitted by insects

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19
Q

5 Examples of arboviruses

A 
Yellow fever
Dengue
West Nile
Zika
Chikingunya
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20
Q

What type of viruses are arboviruses?

A

Flaviviruses

Alphaviruses

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21
Q

What kind of genome do arboviruses have?

A

Positive sense RNA genome

22
Q

Why is there an increasing prevalence of arboviruses?

A 
Global warming
Decrease in mosquito control
Imports
Stagnant water in large cities
Dams
23
Q

What is the vector for west nile virus?

A

Mosquito (Culex tarsalis)

24
Q

What are dead end hosts for west nile virus?

A

Humans

Horses

25
Q

What type of virus is west nile virus?

A

Flavavirus

26
Q

What does Dengue Haemorrhagic fever result from?

A

2nd exposure to different serotype of Dengue

27
Q

How many types of cross reactivity are there in dengue virus?

A

4

28
Q

Risk factors for dengue haemorrhagic fever

A 
Virus strain
Pre-existing anti-dengue antibody
Previous infection
Maternal antibodies in infants
Age
29
Q

Dengue antibodies can either

A

neutralise infection
or
enhance infection

30
Q

What would happen if you had antibodies against Dengue Type 1
But now being infected with Type 2

A

Type 1 antibody binds to Type 2 virus
By Fc portion of antibody, virus gets taken into cells e.g. Macrophage
Kicks off immune response:
Macrophage creates cytokine storm causing endothelial leakage and haemorrhage

31
Q

What type of virus is Chikingunya?

A

Alphavirus

32
Q

What symptoms are associated with Chikingunya?

A

Arthralgia:
Rashes
Headaches
Joint pain

33
Q

What is the vector for Dengue, Zika and Chikingunya?

A

Mosquito

34
Q

What symptoms are associated with Zika?

A 
Headache
Pale skin, rash
Fever
Muscle pain
Diarrhoea
Red eyes
35
Q

Which human viruses recently emerged from animal sources?

A 
SARS-CoV (Bats)
HIV (Chimpanzees)
Ebola
Hendra
Nipah
36
Q

Where did SARS emerge and where has it crossed to?

A

Emerged from bats

Crossed to humans

37
Q

Severe acute respiratory syndrome (SARS) virus

A

Large (30kb)
Positive sense RNA genome.
Envelope spike protein.
Receptor is human ACE-2 protein.

38
Q

What type of virus is SARS?

A

Coronavirus

39
Q

What allows SARS to overcome host range barriers?

A

S protein is highly plastic and can adapt to different receptors

40
Q

How was the outbreak of SARS controlled?

A

By isolation

After discovery that patients only contagious when symptomatic

41
Q

What can SARS lead to?

A

Destruction of lung tissue from overexuberant immune response

42
Q

What type of virus is MERS?

A

Coronavirus

43
Q

How did MERS emerge?

A

It is a zoonosis from camels

44
Q

Recombination of 2 or more viruses

A

Gives rise to a new virus with new properties

45
Q

Pandemic

A

worldwide spread of a new disease

46
Q

Could MERS be the next pandemic?

A

Limited transmission
Diverse clinical signs
No vaccine, no antiviral

47
Q

Could H7N9 be the next pandemic?

A

Limited transmission
No vaccine but technology to make one is known
Antivirals but resistance tolerated.

48
Q

What caused MERS to be spread beyond the Middle East?

A

Health tourism and business travel

49
Q

What amplified the spread of SARS in hospitals?

A

Use of nebulizers

50
Q

Give 2 examples where man’s intervention has been the cause of emerging viruses

A

Myxoma Virus released for rabbit control is Australia

GM created a transmissible H5N1 influenza virus

Microbiology (9 decks)

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