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KMMS FHD > Virus > Flashcards

Virus Flashcards

1
Q

What is viral latency?

A

Virus lies dormant (latent) within a cell

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2
Q

What are the 7 stages of viral replication?

A
  1. Attachment
  2. Penetration (endocytosis)
  3. Uncoating ( viral contents released)
  4. Transcription/ mRNA production
  5. Synthesis of virus components
  6. Virion assembly
  7. Release (liberation stage)
  8. Absorption
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3
Q

What are the four types of viruses?

A
  1. Icosahedral
  2. Helical
  3. Helical and icosahedral (bacteriophage)
  4. Enveloped (Virion, Extracellular)
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4
Q

Viruses can be categorised dependent on their shape or sizes. What are the 4 groups?

A
  1. filamentous
  2. isometric (or icosahedral)
  3. enveloped
  4. head and tail (icosahedral and helical)
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5
Q
  • dsDNA and ssDNA

- genome must be transcribed into mRNA prior to viral replication

A

DNA viruses

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6
Q

What are the (7) Baltimore groups?

A
  1. DNA viruses
  2. RNA viruses
  3. Retroviruses
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7
Q

This is defined as processes by which viral infection results in a disease

A

Viral pathogenesis

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8
Q

What are the three requirements for successful infection?

A
  1. Sufficient virus
  2. Cells accessible, susceptible, permissive
  3. Local antiviral defence absent or overcome
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9
Q

What are the 6 ways of transmission

A
  1. Horizontal
  2. Zoonotic
  3. Latrogenic
  4. Nosocomial
  5. Vertical
  6. Germ Line
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10
Q

transmission between members of the same species

A

Horizontal transmission

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11
Q

transmission between members of different species (animals to humans)

A

zoonotic transmission

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12
Q

Transmission by which an individual is infected while in hospital or health care facility

A

Nosocomial Transmission

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13
Q

Activity of healthcare workers leads to infection of the patient (transmission)

A

Latrogenic Transmission

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14
Q

Transmission by which transfer of infection between parent and offspring

A

Vertical Transmission

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15
Q

agent transmitted as part of the genome

A

Germ line Transmission

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16
Q
  • 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​
  • Absorptive area of lung: 140 m2; –Ventilation rate 6 L/min (0.5 L per breath)q
A

Infiltration by Respiratory Tract

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17
Q

What are the barriers of infection in the respiratory tract?

A
  1. swallowing
  2. ciliary action from lower tract
  3. macrophages in alveoli
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18
Q

Why there is good chance of viral/cell interaction in the alimentary tract?

A

The alimentary tract is designed to mix, digest, absorb food, so contents are always in motion – great for viral/cell interactions​

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19
Q

What are the barriers of infection in the alimentary tract? What makes it a hostile environment?

A

Hostile environment: stomach is acidic, intestine is alkaline; presence of digestive enzymes, bile detergents, mucus, antibodies, phagocytic cells​

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20
Q
  • 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)​
A

Urogenital Tract

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21
Q

How virus can enter the eye?

A

By the sclera and conjunctiva route

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22
Q

Hoe does infection in the ye usually occur?

A

Infection usually occurs after injury and/or ophthalmologic procedures.​

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23
Q

What are disseminated infections in the eye?

A

enterovirus 70 spread to CNS

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24
Q

Virus HSV-1, target, result?

A

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

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25
Q

How does virally entry usually occur in the skin?

A

Viral entry usually occurs by breaks or punctures in the skin or skin abrasions; insect or animal bites; needle punctures.​

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26
Q

Why does infection occur in the skin?

A

Outer layer of dead cells cannot support infection ​

Epidermis is devoid of blood or lymphatics - so local replication only.​

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27
Q

Hoe does viral infection in the skin spread?

A

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

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28
Q

Some viruses spread beyond the primary site

A

Disseminated viral spread

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29
Q

many organs are infected by virus

A

Systemic viral spread

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30
Q

How the integrity of the basement membrane can be compromised?

A

Below the epithelium is the basement membrane; integrity can be compromised by epithelial inflammation and destruction​

Below basement membrane are subepithelial tissues, where virus encounters tissue fluids​

Role of directional release of virus from polarized cells e.g. epithelial cells, neurons etc.​

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31
Q
  • 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)​

​

A

Hematogenous spread​

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32
Q

How can viruses enter blood directly through capillaries?

A

by replicating in endothelial cells, or through vector bite

33
Q

How can the virus easily spread to the blood?

A

Virus enters lymphatic system, as it is more permeable that circulatory capillaries. Viruses can replicate in immune cells (in lymph nodes) and spread infection to distant tissues.

34
Q

Presence of infectious virus in the blood

A

Viremia

35
Q

This results from virus replication (measles)​

A

Active viremia

36
Q

This results from virus introduced into the blood without replication (Dengue Virus)​

A

Passive Viremia

37
Q

An antibody that defends a cell from a pathogen or infectious particle by neutralizing any effect it has biologically.

A

Neutralizing antibody (NAb)

38
Q

How does an NAb recognise viruses?

A

NAb recognize proteins or glycoproteins on the virion surface of enveloped viruses or non-enveloped viruses- so blocking these proteins which enable the entry of the virus into the cell

39
Q
  • Viral entry to local nerve endings​
  • Definitive characteristic of pathogenesis​
  • For other viruses invasion of the CNS is an infrequent diversion from normal replication​
A

Neural Spread

40
Q

Examples of viruses that infect neural tissue

A

rabies, alpha herpesviruses

41
Q

Examples of non-primary CNS replication

A

Poliovirus, reovirus

42
Q

What are the three ways viruses can spread to the CNS?

A
  1. Neural
  2. Olfactory
  3. Hematogenous
43
Q

Poliovirus, yellow fever virus, mouse hepatitis virus, Venezuelan encephalitis virus, rabies virus, reovirus (type 3 only; type 1 spread by viremia), herpes simplex virus types 1 and 2, pseudorabies virus​

(Poliovirus, rabies virus)

A

Neural virus spreading to CNS

44
Q

Poliovirus, herpes simplex virus, coronavirus​

Coronavirus

A

Olfactory virus spreading to the CNS

45
Q

Poliovirus, coxsackievirus, arenavirus, mumps virus, measles virus, herpes simplex virus, cytomegalovirus​

(Measles virus)

A

Hematogenous virus spreading to the CNS

46
Q

(Infections of the CNS)

A ______ virus can infect neural cells (infection may occur by neural or hematogenous spread from a peripheral site)​

A

Neurotropic

47
Q

(Infections of the CNS)

A _______ virus can enter the CNS after infection of a peripheral site​

A

Neuroinvasive

48
Q

(Infections of the CNS)

A _________ virus can cause disease of nervous tissue​

A

Neurovirulent

49
Q

(Infections of the CNS)

HSV: ___ neuroinvasiveness, ____neurovirulence​

A

HSV: low neuroinvasiveness, high neurovirulence​

50
Q

(Infections of the CNS)

Mumps: ____ neuroinvasiveness, _____ neurovirulence

A

Mumps: high neuroinvasiveness, low neurovirulence

51
Q

(Infections of the CNS)

Rabies: _____ neuroinvasiveness, _______ neurovirulence​

A

Rabies: high neuroinvasiveness, high neurovirulence​

52
Q

The spectrum of tissues infected by a virus​.
An enteric virus replicates in the gut and not in the lung; a neurotropic virus replicates in cells of the nervous system and not in hematopoietic cells

A

Tissue Tropism

53
Q

The tropism of some viruses is limited while other viruses are ________ (can replicate in many organs- e.g. Ebola)​

A

Pantropic

54
Q

What are the 3 determinants of viral tropism?​

A
  1. Cell receptors for viruses​
  2. Cellular proteins that regulate viral transcription​
  3. Cellular proteases involved in the maturation of virions​
55
Q

The capacity of a virus to cause disease in an infected host. How badly virus can affect

A

Viral virulence​

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

56
Q

How is virulence quantitated?

A

–LD50 (Lethal Dose 50%; amount of virus needed to kill 50% of infected hosts)

–the mean time to death​
–the mean time to appearance of symptoms​
–measurement of fever, or weight loss​

–measurement of pathological lesions (poliovirus); reduction in blood CD4+ lymphocytes (HIV-1)

57
Q

What makes viruses virulent?

A

Virulence genes are usually identified by mutation: deletion or disruption of one of these genes results in a virus that causes reduced or no disease in a specified system​

58
Q

Viral genes affecting virulence fall into four classes. What are the four 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

59
Q

What are some genes that modify the host’s defence mechanisms?

A

Virokines and viroceptors​

60
Q

Mimic normal cellular molecules critical to host defense​
– sabotage the body’s innate and adaptive defenses​
– not required for growth in cell culture​

A

Virokines and viroceptors

61
Q

Examples of virokines and viroceptors

A

– soluble cytokine receptor - bind cytokines, block action​
– proteins that bind key proteins in complement cascade​
– proteins that affect MHC-1 antigen presentation​

62
Q

Give an example of a toxic viral protein

A

NSP4

63
Q

-Nonstructural glycoprotein of rotaviruses: a viral enterotoxin​
When expressed in cells, causes increase in intracellular calcium.​

  • When fed to young mice, causes diarrhea by potentiating chloride secretion.
  • Triggers a signal transduction pathway in intestinal mucosa​
A

NSP4

64
Q

How the virus is shed (virus shedding)

A
  1. Respiratory secretions (aerosols produced by coughing, sneezing, speaking​
  2. Nasal secretions contaminating hands, tissues
  3. Mucosal shedding
  4. Urine
  5. Semen
  6. Faeces
65
Q

How have host cells evolved to eradicate intruding viruses?

A
  • developed intricate signaling networks to detect, control
  • E.g. Interferons are signaling proteins released by host cells in response to viruses (to increase anti-viral response)​
66
Q

A disease caused by bacteria, viruses or parasites, that can spread from animals to humans​.
-Examples – Ebola, Bird Flu, SARS-CoV2​

A

Zoonosis

Zoonotic viruses are often RNA based – which accounts for their adaptability.

67
Q

What types of specimens are collected to diagnose ? ​

A
  1. Respiratory tract: Nasal and bronchial washings, throat and nasal swabs, sputum​
  2. Eye: throat and eye swab/scraping​
  3. Gastrointestinal tract: stool and rectal swabs​
  4. Vesicular rash: vesicle fluid, skin scrapings​
  5. Maculopapular rash: throat, stool, and rectal swabs​
  6. CNS: stool, tissue, saliva, brain biopsy, cerebrospinal fluid​
  7. Genital: vesicle fluid or swab​
  8. Urinary tract: urine​
  9. Blood borne: blood
68
Q

How are viruses tested?

A
  • Detection of antibody mounted against the virus​
  • Detection of viral protein (antigen)​
  • Detection of viral nucleic acid
69
Q

How is viral antigen detected?

A
  • Immunofluorescence​
  • sputum sample
  • quick test, but needs manufacturing of specific monoclonal antibodies
  • need expert personnel and fluorescent microscope set up
70
Q

How is viral antibody detected?

A
  • Commonest test used is the enzyme-linked immunosorbent assay (ELISA
  • The coupled enzyme is usually HRP that causes a chemical reaction in the presence of dye – allowing visualization of the result. ​
71
Q

How does ELISA work?

A
  1. Substrate changes colour when cleaved by the enzyme attached to the second antibody
  2. Anti-human immunoglobulin (2nd antibody) coupled to an enzyme​
  3. Patient serum contains antibodies​
  4. Purified antigens pre-coated onto an ELISA plate​
72
Q

Automation and random access analyser​

A

Can run multiple serological tests for different viruses simultaneously​

73
Q

What’s the Commonest test used is polymerase chain reaction (PCR)?

A

Viral nucleic acid detection​

-quantify virus/viral load

74
Q

What viruses is the Viral nucleic acid detection for?

A
  • All viruses especially non-cultivable viruses

- Viruses in low copy numbers

75
Q

What is the SARS-CoV2 PCR testingmethod?

A

Viral nucleic acid detection​

76
Q

General Methods by which virus infections or spread can be limited

A
  • Medical mask
  • Gloves
  • Overalls
  • goggles
  • surgical cap
  • apron
77
Q

What are some long-term and short term specific measures for viral prevention?

A

vaccines, chemoprophylaxis, immunoprophylaxis​

78
Q

Give some examples of Germ Line Transmission

A

*

KMMS FHD (30 decks)

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