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Foundations of health and disease > viruses > Flashcards

viruses Flashcards

1
Q

What is the structure of viral particles?

A

Viral particles are small, ranging in size from 20nm to 900nm. Examples include Atadenovirus and HIV retrovirus.

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2
Q

What is viral latency?

A

Viral latency refers to a state in which the virus lies dormant (latent) within a cell. Each step of viral replication is described in the slide note.

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3
Q

What is the significance of RNA-based viruses?

A

RNA-based viruses have a greater mutation rate and can adapt rapidly to their environment.

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4
Q

What is viral pathogenesis?

A

Viral pathogenesis refers to the processes by which viral infection leads to the development of a disease.

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5
Q

What are the two components of viral disease?

A

The two components of viral disease are the effects of virus replication on the host and the effects of the host response on the virus and the host.

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6
Q

What are the three requirements for a successful infection?

A

The three requirements for a successful infection are:

Sufficient virus
Cells that are accessible, susceptible, and permissive
Absence or overcoming of local antiviral defense mechanisms.

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7
Q

What is horizontal transmission?

A

Horizontal transmission refers to the transmission of a virus between members of the same species.

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8
Q

What is zoonotic transmission?

A

Zoonotic transmission refers to the transmission of a virus between members of different species, such as from animals to humans.

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9
Q

What is iatrogenic transmission?

A

Iatrogenic transmission occurs when the activities of a healthcare worker lead to the infection of a patient.

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10
Q

What is nosocomial transmission?

A

Nosocomial transmission refers to the transmission of an infection to an individual while they are in a hospital or healthcare facility.

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11
Q

What is vertical transmission?

A

Vertical transmission is the transfer of an infection from a parent to their offspring, typically occurring during pregnancy, childbirth, or breastfeeding.

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12
Q

What is germ line transmission?

A

Germ line transmission refers to the transmission of an infectious agent as part of the genome, typically inherited from one generation to the next.

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13
Q

What is the most common route of viral entry into the body?

A

The respiratory tract is the most common route of viral entry into the body.

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14
Q

How do viruses enter the respiratory tract?

A

Viruses can enter the respiratory tract through aerosolized droplets from coughing or sneezing, or through direct contact with saliva.

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15
Q

Where do large droplets typically lodge in the respiratory tract?

A

Large droplets tend to lodge in the nose.

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16
Q

Where do smaller droplets tend to lodge in the respiratory tract?

A

Smaller droplets can lodge in the airways or alveoli of the lungs.

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17
Q

How do viruses enter the alimentary tract?

A

Viruses can enter the alimentary tract through activities such as eating, drinking, and social interactions, providing good opportunities for virus-cell interactions.

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18
Q

What is the nature of the alimentary tract environment for viruses?

A

The alimentary tract is an extremely hostile environment for viruses.

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19
Q

Are there viruses that have evolved to infect the alimentary tract despite the hostile environment?

A

Yes, some viruses have evolved to infect the alimentary tract and are resistant to the factors present in this environment.

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20
Q

What protects the urogenital tract from viral infections?

A

The urogenital tract is protected by mucus and has a low pH, which helps prevent viral infections.

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21
Q

How can viruses enter the urogenital tract?

A

Minute abrasions from sexual activity may allow viruses to enter the urogenital tract.

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22
Q

What are some examples of viruses that can produce local lesions in the urogenital tract?

A

Human papillomavirus (HPV) is an example of a virus that can produce local lesions in the urogenital tract.

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23
Q

Can viruses spread from the urogenital tract to other parts of the body?

A

Yes, some viruses can spread from the urogenital tract to other parts of the body. An example is the human immunodeficiency virus (HIV).

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24
Q

How do viruses enter the eye?

A

The entry route for viruses into the eye is through the sclera and conjunctiva.

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25
Q

When does infection typically occur in the eye?

A

Infection in the eye usually occurs after injury and/or ophthalmologic procedures.

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26
Q

Can viruses cause disseminated infections and affect the central nervous system?

A

Yes, some viruses, such as enterovirus 70, can cause disseminated infections and spread to the central nervous system.

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27
Q

Can herpes simplex virus type 1 (HSV-1) infect the eye?

A

Yes, HSV-1 can infect the cornea, and if left untreated, it can lead to blindness. The virus can also spread to the sensory ganglia.

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28
Q

Can the outer layer of dead cells in the skin support viral infection?

A

No, the outer layer of dead cells in the skin cannot support viral infection

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29
Q

Which part of the skin is devoid of blood or lymphatics, allowing for local replication only?

A

The epidermis, which is the outermost layer of the skin, is devoid of blood or lymphatics, allowing for local replication of viruses.

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30
Q

In which layer of the skin can infection spread due to high vascularity?

A

: Infection can spread in the dermis and sub-dermal tissues of the skin, as these areas are highly vascularized.

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31
Q

How do some viruses spread beyond the primary site or infect multiple organs?

A

Some viruses can spread beyond the primary site of infection or infect multiple organs. This occurs when the viruses breach physical and immune barriers.

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32
Q

How do viruses that produce disseminated infection often spread?

A

Viruses that produce disseminated infection often enter the bloodstream, allowing them to spread to various organs and tissues.

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33
Q

How are viruses in extracellular fluids taken up by the lymphatic system?

A

Viruses in extracellular fluids are taken up by lymphatic capillaries, which helps facilitate their spread.

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34
Q

Once in the bloodstream, what access does the virus have?

A

Once in the bloodstream, the virus has access to almost every tissue in the body.

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35
Q

Do all viruses spread freely in the blood?

A

No, not all viruses spread freely in the blood. Some viruses can establish viremia, which means they circulate in the blood, while others may be contained or limited in their spread.

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36
Q

What is viremia?

A

Viremia refers to an infectious virus in the blood.

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37
Q

What is active viremia?

A

Active viremia results from virus replication within the body, such as measles.

38
Q

What is passive viremia?

A

Passive viremia occurs when the virus is introduced into the blood without replication, as seen with Dengue Virus.

39
Q

In terms of diagnosis, what does viremia help determine?

A

Viremia helps determine where the virus is located in the body. Examples include influenza and poliovirus.

40
Q

How does neural spread occur?

A

Neural spread occurs when the virus enters local nerve endings and spreads through the neural pathways.

41
Q

What can neural spread be considered in terms of pathogenesis?

A

Neural spread can be the definitive characteristic of pathogenesis for certain viruses.

42
Q

Is invasion of the central nervous system (CNS) common for all viruses?

A

No, for many viruses, invasion of the CNS is an infrequent diversion from their normal replication.

43
Q

What are some pathways through which viruses can spread to the CNS?

A

Some pathways for viral spread to the CNS include neural, olfactory, and hematogenous.

44
Q

Which viruses can spread to the CNS through neural pathways?

A

Viruses such as poliovirus, yellow fever virus, mouse hepatitis virus, Venezuelan encephalitis virus, rabies virus, reovirus (type 3 only; type 1 spreads by viremia), and herpes simplex virus types 1 and 2 can spread to the CNS through neural pathways.

45
Q

Which viruses can spread to the CNS through the olfactory pathway?

A

Viruses like poliovirus, herpes simplex, and coronavirus can spread to the CNS through the olfactory pathway.

46
Q

Which viruses can spread to the CNS through hematogenous spread?

A

Viruses, including poliovirus, coxsackievirus, arenavirus, mumps virus, measles virus, herpes simplex virus, and cytomegalovirus, can spread to the CNS through hematogenous spread.

47
Q

What is a neurotropic virus?

A

A neurotropic virus is a virus that can infect neural cells. Infection may occur by neural spread (directly targeting the CNS) or hematogenous spread from a peripheral site.

48
Q

What is a neuroinvasive virus?

A

A neuroinvasive virus is a virus that can enter the CNS after initially infecting a peripheral site outside the CNS.

49
Q

What is a neurovirulent virus?

A

A neurovirulent virus is a virus that can cause disease, specifically in nervous tissue.

50
Q

What is tissue tropism?

A

Tissue tropism refers to the spectrum of tissues infected by a virus.

51
Q

What is the difference between limited tropism and pantropism?

A

Some viruses have limited tropism, meaning they can only replicate in specific organs or tissues, while others are pantropic and can replicate in many organs. An example of a pantropic virus is Ebola.

52
Q

What are the determinants of viral tropism?

A

The determinants of viral tropism include:

Cell receptors for viruses
Cellular proteins that regulate viral transcription
Cellular proteases involved in the maturation of virions

53
Q

What is viral virulence?

A

Viral virulence refers to the capacity of a virus to cause disease in an infected host.

54
Q

What is the difference between virulent and avirulent or attenuated viruses?

A

A virulent virus causes significant disease in the infected host, while an avirulent or attenuated virus causes reduced or no disease.

55
Q

How can virulence be quantitated?

A

Virulence can be quantitated using various measurements, including:

LD50 (Lethal Dose 50%): the amount of virus needed to kill 50% of infected hosts
Mean time to death
Mean time to appearance of symptoms
Measurement of fever or weight loss
Measurement of pathological lesions (e.g., poliovirus)
Reduction in blood CD4+ lymphocytes (e.g., HIV-1)

56
Q

What is a major goal of virology in studying virulence?

A

A major goal of virology is to identify viral and host genes that determine virulence.

57
Q

How are virulence genes usually identified?

A

Mutations usually identify virulence genes. Deleting or disrupting one of these genes can result in a virus that causes reduced or no disease in a specified system.

58
Q

What are the four classes of viral genes affecting virulence?

A

The four classes of viral genes affecting virulence are:

Genes that affect the ability of the virus to replicate.
Genes that modify the host’s defence mechanisms.
Genes that enable the virus to spread in the host.
Genes that have intrinsic cell-killing effects.

59
Q

What are virokines and viroceptors?

A

Virokines and viroceptors are viral proteins that mimic normal cellular molecules critical to host defence. They sabotage the body’s innate and adaptive defences and are not required for viral growth in cell culture.

60
Q

Can you provide examples of viral proteins that modify host defence mechanisms?

A

Examples include soluble cytokine receptors that bind cytokines and block their action, proteins that bind key proteins in the complement cascade, and proteins that affect major histocompatibility complex class I (MHC-I) antigen presentation.

61
Q

What are some ways in which viruses are shed from an infected host?

A

Viruses can be shed through various routes, including respiratory secretions, mucosal shedding, urine, semen, faeces, skin lesions, and blood.

62
Q

What are some mechanisms of virus shedding?

A

Virus shedding can occur through respiratory secretions, mucosal shedding, urine, semen, faeces, skin lesions, blood, blood supply, insect vectors, germline (transmission from parent to offspring), and vertical transmission.

63
Q

How are respiratory secretions involved in virus shedding?

A

Virus shedding can occur through respiratory secretions, which are aerosols produced by coughing, sneezing, and speaking. Nasal secretions can also contaminate hands and tissues, contributing to virus transmission.

64
Q

How do viruses interact with host factors during replication?

A

Viruses have evolved to hijack host factors to facilitate their replication. They exploit the cellular machinery of host cells for their reproduction and survival.

65
Q

What is the role of interferons in host-virus interactions?

A

Interferons are signalling proteins host cells release in response to viruses. They play a crucial role in increasing the host’s antiviral response, helping to control and eradicate invading viruses.

66
Q

What is the nature of the relationship between viruses and hosts at the molecular and cellular level?

A

The interaction between viruses and hosts is an ongoing evolutionary arms race at the molecular and cellular levels. Viruses constantly evolve strategies to evade host defences, while hosts develop intricate signalling networks to detect, control, and eliminate invading viruses.

67
Q

What are zoonotic viruses?

A

Zoonotic viruses are pathogens that can spread from animals to humans, causing diseases. They include bacteria, viruses, and parasites.

68
Q

Can you provide examples of zoonotic viruses?

A

Examples of zoonotic viruses include Ebola virus, Bird Flu (avian influenza), and SARS-CoV-2 (the virus causing COVID-19).

69
Q

What is the adaptability of zoonotic viruses attributed to?

A

Zoonotic viruses are often RNA-based, which accounts for their adaptability. RNA viruses tend to have a higher mutation rate, allowing them to adapt more readily to new environments and potentially cross species barriers.

70
Q

What types of specimens are commonly collected for diagnostic testing?

A

Specimens collected for diagnostic testing can vary depending on the suspected site of infection. Examples include respiratory tract specimens (nasal and bronchial washings, throat and nasal swabs, sputum), eye specimens (throat and eye swabs/scrapings), gastrointestinal tract specimens (stool and rectal swabs), vesicular rash specimens (vesicle fluid, skin scrapings), maculopapular rash specimens (throat, stool, and rectal swabs), CNS specimens (stool, tissue, saliva, brain biopsy, cerebrospinal fluid), genital specimens (vesicle fluid or swab), urinary tract specimens (urine), and blood specimens.

71
Q

What are some old methods used for viral testing?

A

Some old methods for viral testing include microscopy and culture, where the virus is observed directly under a microscope or cultured in specific laboratory conditions.

72
Q

What are some current methods used for viral testing?

A

Current methods for viral testing include:

Detection of antibodies mounted against the virus
Detection of viral protein (antigen)
Detection of viral nucleic acid (genetic material)

73
Q

How is viral antigen detected using immunofluorescence?

A

Viral antigens can be detected using immunofluorescence, where specific monoclonal antibodies are used. This method requires a fluorescent microscope setup and expert personnel.

74
Q

What are some advantages of immunofluorescence for detecting viral antigens?

A

Immunofluorescence allows for quick testing. However, it may not be applicable to all viruses, as specific monoclonal antibodies need to be manufactured for each virus.

75
Q

Can you provide an example of a sample for which immunofluorescence can be used?

A

Sputum samples can be tested using immunofluorescence to detect viral antigens.

76
Q

Why is expertise required for interpreting immunofluorescence results?

A

Expert personnel are needed to interpret immunofluorescence results, as they require specialised training and experience in using the fluorescent microscope and analysing the fluorescent patterns.

77
Q

What is the importance of cluster analysis in sample testing?

A

Cluster analysis helps identify patterns and relationships between samples, aiding in identifying and tracking viral outbreaks or transmission clusters.

78
Q

What is the common test for detecting antibodies or antigens in serum or plasma?

A

The enzyme-linked immunosorbent assay (ELISA) is the common test for detecting antibodies or antigens in serum or plasma.

79
Q

What is the process of ELISA?

A

Purified antigens are pre-coated onto an ELISA plate. Patient serum, which contains antibodies, is added. An anti-human immunoglobulin 2nd antibody coupled with an enzyme is added. The substrate, which changes colour when cleaved by the enzyme attached to the second antibody, is added.

80
Q

How is serology testing made more efficient?

A

Automation and random access analysers can run multiple serological tests for different viruses simultaneously, allowing for more efficient testing.

81
Q

What is the common test used for viral nucleic acid detection?

A

Polymerase chain reaction (PCR) is the common viral nucleic acid detection test.

82
Q

What are the advantages of PCR testing?

A

PCR testing is quick, with results available within 24 hours. It is particularly helpful for non-cultivable viruses and quantifies the viral load.

83
Q

Can you provide an example of PCR testing in use?

A

PCR testing for SARS-CoV-2 (the virus causing COVID-19) is widely used for diagnosis and surveillance during the current pandemic.

84
Q

How can viral infections/diseases be prevented?

A

Viral prevention measures include general measures such as wearing gloves and masks and specific measures like vaccines, chemoprophylaxis, and immunoprophylaxis.

85
Q

What are some examples of specific measures for viral prevention?

A

Examples of specific measures for viral prevention include vaccines, which provide long-term prevention, and chemoprophylaxis or immunoprophylaxis, which offer short-term prevention.

86
Q

What measures were taken for viral prevention during the current SARS-CoV-2 pandemic?

A

Measures during the SARS-CoV-2 pandemic include social interventions, physical distancing, wearing masks, and maintaining hygiene practices to prevent viral transmission.

87
Q

What is the role of personal protective equipment (PPE)?

A

Personal protective equipment protects individuals from exposure to infectious agents, including viruses like Ebola. It includes garments, masks, gloves, goggles, and other items.

88
Q

How do vaccines work against viral infections?

A

Vaccines stimulate the immune system to recognise and mount a response against specific viral antigens, inhibiting the virus and reducing symptoms in individuals affected by viral infections.

89
Q

What are the different types of vaccines available?

A

Vaccines can be made from live viruses (e.g., oral polio vaccine), killed viruses, or molecular subunits of the virus. Examples of vaccines available include MMR (measles, mumps, and rubella), HBV (hepatitis B), HPV (human papillomavirus), Varicella Zoster Virus (chickenpox and shingles), Rotavirus, and SARS-CoV-2 vaccines.

90
Q

Why does the influenza vaccine need to be updated annually?

A

The influenza virus undergoes frequent changes, leading to the need for annual updates in the influenza vaccine to match the circulating strains.

91
Q

Are there vaccines available for all viruses?

A

No, vaccines are not available for all viruses. For example, there is currently no vaccine available for HIV.

92
Q

What are some examples of antiviral drugs?

A

Examples of antiviral drugs include:

HAART drugs for HIV (not curative, but help reduce viral load)
Lamivudine and others for HBV
Ribavirin and PEG IFN for HCV
Tamiflu and others for influenza
Aciclovir and others for HSV
Ganciclovir and others for CMV
PF-07321332, PAXLOVID, and viral protease inhibitors for SARS-CoV-2.

Foundations of health and disease (45 decks)

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