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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
what is passive viremia
results from virus introduced into the blood without replication
26
what is neural spread of viruses
viral entry to local nerve endings
27
what is a neuroinvasive virus
a virus that can enter the CNS after infection of a peripheral site
28
what is a neurovirulent virus
a virus that can cause disease of nervous tissue
29
what is tissue tropism
the spectrum of tissues infected by a virus
30
what are pantopic viruses
a virus that can replicate in many organs
31
what is determines a virus
Cell receptors for viruses Cellular proteins that regulate viral transcription Cellular proteases involved in the maturation of virions
32
what is viral virulence
The capacity of a virus to cause disease in an infected host
33
what is the difference between a virulent, avirulent and attenuated virus
A virulent virus causes significant disease, while an avirulent or attenuated virus causes reduced or no disease
34
how is virulence quantified
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)
35
what are the Viral genes affecting virulence classes
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
what are features of virokines and viroreceptors
Mimic normal cellular molecules critical to host defense sabotage the body’s innate and adaptive defenses not required for growth in cell culture
37
how do you detect an antibodu in the plasma
via serolology
38
explain the steps of ELISA
it is an enzyme-linked immunosorbent assay substrate changes colour when enzyme is removed
39
how do you detect a viral antigen
immunoflouresence need manufacturing of specific monoclonal antibodies
40
how do you collect specimens from respiratory tract
Nasal and bronchial washings, throat and nasal swabs, sputum
41
how do you collect specimens from the eye
throat and eye swab/scraping
42
how do you collect specimens from the gastrointestinal tract
stool and rectal swabs
43
how do you collect specimens from the vesicular rash
vesicle fluid and skin scrapings
44
how do you collect specimens from maculpapular
throat, stool and rectal swabs
45
how do you collect specimens from the CNS
stool,tissue, saliva, brain biopsy and cerebrospinal fluid
46
how do you collect specimens from the gentials
vesicle fluid or swab
47
how do you collect specimens from urinary tract
urine
48
how do you collect specimens from blood borne
blood
49
what are measures to prevent viral infection
General measures e.g. gloves, masks, etc Specific measures (long-term or short-term prevention) e.g. vaccines, chemoprophylaxis, immunoprophylaxis
50
how long does it take to get any information from an infection
24 hours
51
how long does it take to get definitive information about an infection
48 hours
52
what information is required to treat an infection
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
what are the situations where you use a special stain
Other organisms eg TB Electron microscopy for viruses Direct visualisation of parasites and eggs
54
what is an API test
API (analytical profile index) strips give accurate identifications based on extensive databases and are standardized, easy-to-use test systems.
55
what are the advantages and disadvantages of API's
Good for detecting bacteria you can stain and grow Reliable identification and resistance testing Can be slow and labour intensive
56
what is PCR
PCR is a technique that takes a specific sequence of DNA of small amount and amplifies it to be used for further testing.
57
what is the purpose of PCR
To amplify double-stranded DNA molecules with the same (identical) size and sequence by enzymatic method and cycling condition.
58
what are the steps of PCR
1. Denaturation of ds DNA template 2. Annealing of primers 3. Extension of ds DNA molecules
59
Explain denaturation in PCR
Temperature: 92 – 95°C Double-stranded DNA melts -> single stranded DNA
60
explain annealing in PCR
Temperature: 50 – 70°C (depending on the melting temperature of the expected duplex) Primers bind to their complementary sequences
61
explain extension in PCR
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
why do you do whole genome sequencing
Sequencing entire DNA of bacteria and viruses Compare strains to see how related they are/evolve Interrogate for antibiotic resistance genes
63
what are the advantages of whole genome sequencing
Set to revolutionise diagnosis of infection Rapid (hours) Cheap (comparable to culture) Desktop Platforms
64
what are you usually investigating using tissue cultures
Cytopathic effects on cells Expression of viral proteins detected at the cell surface
65
what is infection classified by
are classified by the causative agent as well as by the symptoms that are produced.
66
what is an apparent infection
one that produces symptoms
67
what can an infection that is active, but does not produce noticeable symptoms called
apparent, silent or subclinical
68
what is a latent infection
an infection that is inactive or dormant
69
what is the pathway of infection
mode of transmission portal of entry susceptible host causative agent reservoir portal of exit
70
how to break the chain of infection from a causative agent
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
what is a reservoir
A reservoir is the place where the agent survives, grows, and/or multiplies: human, animal or environment.
72
how do you break the chain of infection from the reservoir
Occupational health: Immunization and regular check ups. Environmental disease: Cleaning hospital with disinfectant Clean bed/furniture between patients
73
how do you break the chain of infection from the portal of exit
Practice aseptic precaution Wearing masks Careful handling of waste Wear disposable gloves
74
how do you break chain of infection from mode of transmission
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
how do you break chain of infection from portal of entry
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
how do you break chain of infection from susceptible host
Protecting the susceptible host: Oral hygiene Maintaining adequate intake Encouraging exercise Encouraging immunization Maintaining healing process: Balanced diet Appetite of patient Reduce stress
77
what is an acute infection
sudden and rapid onset of a disease
78
what is a chronic infection
continued infection by the primary agent for a long period- often following primary infection
79
what is primary infection
the initial infection of a host by a pathogen
80
what is a latent infection
a persistent infection that does not have any symptoms after the primary infection
81
what are features of latent infections
DNA viruses or retroviruses Persistence of viral DNA Retrovirus infection may induce cellular transformation
82
what are professional pathogens
almost always cause disease
83
what are opportunitic pathogens
only cause disease in immunocompromised patients
84
what is pathogenicity
the capacity of an organism to cause disease
85
what is virulence
the degree of pathogenicity caused by an organism
86
what is commensal
an organism that recieves benefit from the host without causing harm
87
what does pathogenicity depend on
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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