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Foundations of health and disease > viruses > Flashcards

viruses Flashcards

1
Q

what is viral pathogenesis

A

processes by which viral infection results in a disease.

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2
Q

7 stages of viral replication

A

Adsorption,

Entry,

Uncoating,

Transcription/mRNAproduction,

Synthesis ofviruscomponents,

Virionassembly

Release (Liberation Stage).

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3
Q

what is adsorption in viral replication

A

The virus becomes attached to the cell by specific cellular receptors which can be glycoproteins, phospholipids or glycolipids.

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4
Q

what is entry in viral replication?

A

Following adsorption, the virus can enter the cell, most commonly via receptor-mediated endocytosis. This is the same process by which many hormones enter the cell.

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5
Q

what is uncoating in viral replication

A

Once inside the host cell, the viral capsid must be uncoated to release the viral nucleic acid. Uncoating may be achieved by host or viral enzymes that will degrade the capsid.

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6
Q

what is Transcription/mRNAproduction, synthesis ofviruscomponents

A

Once uncoated, viruses (DNA or RNA) replicate by switching the host machinery from cellular protein synthesis to viral synthesis and viral proteins are produced.

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7
Q

what is Virionassembly in viral replication

A

Newly synthesised viral proteins are post-transcriptionally modified and packaged into virions that can be released from the infected host cell to infect other cells.

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8
Q

what is Release (Liberation Stage) in viral replication

A

Virions are released from the cell either by lysis or budding. In lysis, the infected cell dies and the virions are released. In budding, the virion takes some of the host cell’s membrane with it as it leaves – this normally does not kill the infected cell.

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9
Q

what is Horizontal transmission

A

between members of same species

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10
Q

what is Zoonotic transmission

A

between members of different species

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11
Q

what is Latrogenic

A

activity of health care worker leads to infection of patient

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12
Q

what is Nosocomial

A

when an individual is infected while in hospital or health care facility

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13
Q

what is Vertical transmission

A

transfer of infection between parent and offspring

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14
Q

what is Germ line transmission

A

agent is transmitted as part of the genome

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15
Q

how do you acquire an infection from the respiratory tract

A

Most common route of viral entry
Viruses enter by aerosolized droplets from cough or sneeze, or contact with saliva
Large droplets lodge in nose; smaller in airways or alveoli

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16
Q

how do you acquire an infection from the alimentary tract

A

Eating, drinking, social activities introduce viruses into the alimentary tract.

good opportunities for virus-cell interactions.

Extremely hostile environment.

Viruses that have evolved to infect are resistant to these factors.

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17
Q

how do you acquire an infection from the urogenital tract

A

Protected by mucus, low pH
Minute abrasions from sexual activity may allow viruses to enter
Some viruses produce local lesions (e.g. HPV)
Some viruses spread from urogenital tract (e.g. HIV)

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18
Q

how do you acquire an infection from the eye

A

Sclera and conjunctiva entry route.

Infection usually occurs after injury and/or ophthalmologic procedures.

Disseminated infection: e.g. enterovirus 70 spread to CNS

HSV-1 can infect cornea, blindness may result, virus spread to sensory ganglia

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19
Q

how do you acquire an infection from the skin

A

Outer layer of dead cells cannot support infection
Epidermis is devoid of blood or lymphatics - so local replication only.

Dermis and sub-dermal tissues are highly vascularized - infection may spread.

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20
Q

what is disseminated spread

A

when viruses spread beyond the primary sire

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21
Q

what is systemic spread

A

when viruses infect many organs

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22
Q

what is hematogenous spread?

A

Viruses that produce disseminated infection often do so by entering the blood

Virus in extracellular fluids are taken up by lymphatic capillaries

Once in blood, virus has access to almost every tissue

Other viruses spread freely in the blood
(viremia)

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23
Q

what is viremia

A

Presence of infectious virus in the blood

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24
Q

what is active viremia

A

results from virus replication

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25
Q

what is passive viremia

A

results from virus introduced into the blood without replication

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26
Q

what is neural spread of viruses

A

viral entry to local nerve endings

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27
Q

what is a neuroinvasive virus

A

a virus that can enter the CNS after infection of a peripheral site

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28
Q

what is a neurovirulent virus

A

a virus that can cause disease of nervous tissue

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29
Q

what is tissue tropism

A

the spectrum of tissues infected by a virus

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30
Q

what are pantopic viruses

A

a virus that can replicate in many organs

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31
Q

what is determines a virus

A

Cell receptors for viruses
Cellular proteins that regulate viral transcription

Cellular proteases involved in the maturation of virions

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32
Q

what is viral virulence

A

The capacity of a virus to cause disease in an infected host

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33
Q

what is the difference between a virulent, avirulent and attenuated virus

A

A virulent virus causes significant disease, while an avirulent or attenuated virus causes reduced or no disease

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34
Q

how is virulence quantified

A

LD50 (Lethal Dose 50%; the amount of virus needed to kill 50% of infected hosts)
the meantime to death
the meantime of symptoms
measurement of fever, or weight loss
measurement of pathological lesions (poliovirus); reduction in blood CD4+ lymphocytes (HIV-1)

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35
Q

what are the Viral genes affecting virulence classes

A

Those that affect the ability of the virus to replicate
Those that modify the host’s defense mechanisms
Those that enable the virus to spread in the host
Those which have intrinsic cell killing effects

36
Q

what are features of virokines and viroreceptors

A

Mimic normal cellular molecules critical to host defense

sabotage the body’s innate and adaptive defenses

not required for growth in cell culture

37
Q

how do you detect an antibodu in the plasma

A

via serolology

38
Q

explain the steps of ELISA

A

it is an enzyme-linked immunosorbent assay
substrate changes colour when enzyme is removed

39
Q

how do you detect a viral antigen

A

immunoflouresence
need manufacturing of specific monoclonal antibodies

40
Q

how do you collect specimens from respiratory tract

A

Nasal and bronchial washings, throat and nasal swabs, sputum

41
Q

how do you collect specimens from the eye

A

throat and eye swab/scraping

42
Q

how do you collect specimens from the gastrointestinal tract

A

stool and rectal swabs

43
Q

how do you collect specimens from the vesicular rash

A

vesicle fluid and skin scrapings

44
Q

how do you collect specimens from maculpapular

A

throat, stool and rectal swabs

45
Q

how do you collect specimens from the CNS

A

stool,tissue, saliva, brain biopsy and cerebrospinal fluid

46
Q

how do you collect specimens from the gentials

A

vesicle fluid or swab

47
Q

how do you collect specimens from urinary tract

A

urine

48
Q

how do you collect specimens from blood borne

A

blood

49
Q

what are measures to prevent viral infection

A

General measures e.g. gloves, masks, etc
Specific measures (long-term or short-term prevention) e.g. vaccines, chemoprophylaxis, immunoprophylaxis

50
Q

how long does it take to get any information from an infection

A

24 hours

51
Q

how long does it take to get definitive information about an infection

A

48 hours

52
Q

what information is required to treat an infection

A

A knowledge of what bacteria cause what syndromes of infection (UTI, pneumonia etc)
A knowledge of resistance rates
Diagnostic microbiology
Corrects your initial diagnosis
Allows you to focus your treatment
Informs the epidemiology

53
Q

what are the situations where you use a special stain

A

Other organisms eg TB
Electron microscopy for viruses
Direct visualisation of parasites and eggs

54
Q

what is an API test

A

API (analytical profile index) strips give accurate identifications based on extensive databases and are standardized, easy-to-use test systems.

55
Q

what are the advantages and disadvantages of API’s

A

Good for detecting bacteria you can stain and grow

Reliable identification and resistance testing

Can be slow and labour intensive

56
Q

what is PCR

A

PCR is a technique that takes a specific sequence of DNA of small amount and amplifies it to be used for further testing.

57
Q

what is the purpose of PCR

A

To amplify double-stranded DNA molecules with the same (identical) size and sequence by enzymatic method and cycling condition.

58
Q

what are the steps of PCR

A
  1. Denaturation of ds DNA template
  2. Annealing of primers
  3. Extension of ds DNA molecules
59
Q

Explain denaturation in PCR

A

Temperature: 92 – 95°C

Double-stranded DNA melts -> single stranded DNA

60
Q

explain annealing in PCR

A

Temperature: 50 – 70°C (depending on the melting temperature of the expected duplex)

Primers bind to their complementary sequences

61
Q

explain extension in PCR

A

Temperature: 72°C
Time: 0.5 – 3mins
DNA polymerase binds to the annealed primers and extends the DNA from the 3’ end of the chain

62
Q

why do you do whole genome sequencing

A

Sequencing entire DNA of bacteria and viruses
Compare strains to see how related they are/evolve
Interrogate for antibiotic resistance genes

63
Q

what are the advantages of whole genome sequencing

A

Set to revolutionise diagnosis of infection
Rapid (hours)
Cheap (comparable to culture)
Desktop Platforms

64
Q

what are you usually investigating using tissue cultures

A

Cytopathic effects on cells
Expression of viral proteins detected at the cell surface

65
Q

what is infection classified by

A

are classified by the causative agent as well as by the symptoms that are produced.

66
Q

what is an apparent infection

A

one that produces symptoms

67
Q

what can an infection that is active, but does not produce noticeable symptoms called

A

apparent, silent or subclinical

68
Q

what is a latent infection

A

an infection that is inactive or dormant

69
Q

what is the pathway of infection

A

mode of transmission
portal of entry
susceptible host
causative agent
reservoir
portal of exit

70
Q

how to break the chain of infection from a causative agent

A

Rapid and accurate identification of organism:
Routinely screen samples and equipment.

Control or eliminate infectious agents:
Proper cleaning with water/mechanical action with detergents
Disinfection
Sterilization

71
Q

what is a reservoir

A

A reservoir is the place where the agent survives, grows, and/or multiplies: human, animal or environment.

72
Q

how do you break the chain of infection from the reservoir

A

Occupational health:
Immunization and regular check ups.

Environmental disease:
Cleaning hospital with disinfectant
Clean bed/furniture between patients

73
Q

how do you break the chain of infection from the portal of exit

A

Practice aseptic precaution
Wearing masks
Careful handling of waste
Wear disposable gloves

74
Q

how do you break chain of infection from mode of transmission

A

Contact Precautions:

Single patient room
Good hand hygiene, PPE as appropriate.
Remove PPE when leaving.
Clean and disinfect non-disposable equipment and items

Droplet Precautions:
Single patient room
Surgical masks
Limit patient movement outside the room

Airborne Precautions:
Negative pressure
N95/P2 masks
Limit patient movement outside the room

75
Q

how do you break chain of infection from portal of entry

A

Maintain integrity of skin and mucous membranes
Turning and positioning of debilitated patients
Ensure personal hygiene of patients
Disposal of contaminated sharps
Handling of catheters and drainage

76
Q

how do you break chain of infection from susceptible host

A

Protecting the susceptible host:
Oral hygiene
Maintaining adequate intake
Encouraging exercise
Encouraging immunization

Maintaining healing process:
Balanced diet
Appetite of patient
Reduce stress

77
Q

what is an acute infection

A

sudden and rapid onset of a disease

78
Q

what is a chronic infection

A

continued infection by the primary agent for a long period- often following primary infection

79
Q

what is primary infection

A

the initial infection of a host by a pathogen

80
Q

what is a latent infection

A

a persistent infection that does not have any symptoms after the primary infection

81
Q

what are features of latent infections

A

DNA viruses or retroviruses
Persistence of viral DNA
Retrovirus infection may induce cellular transformation

82
Q

what are professional pathogens

A

almost always cause disease

83
Q

what are opportunitic pathogens

A

only cause disease in immunocompromised patients

84
Q

what is pathogenicity

A

the capacity of an organism to cause disease

85
Q

what is virulence

A

the degree of pathogenicity caused by an organism

86
Q

what is commensal

A

an organism that recieves benefit from the host without causing harm

87
Q

what does pathogenicity depend on

A

The organism’s virulence but also…
Where it is
Immune state of the patient

Foundations of health and disease (21 decks)

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