Introduction to Viruses

Question 1

What can viruses be classified as?

Answer 1

Viron/symmetry
Presence or absence of envelope
Genome structure
Mode of replication

Question 2

What is a viral culture?

Answer 2

A test to find viruses that can cause an infection.

Question 3

What makes a viral culture positive?

Answer 3

If the cells show changes, known as cytopathic effects, then the culture is positive.

Question 4

Describe shell vial culture

Answer 4

The sample is centrifuged onto a single layer of cells and viral growth is measured by antigen detection methods

Question 5

List human virus infections of major importance

Answer 5

COVID-19.
Influenza (the flu)
HIV, which can lead to AIDS.
Meningitis (there is also bacterial meningitis)
Pneumonia (there is also bacterial pneumonia)
Human papillomavirus (HPV)
Herpes
Rotavirus

Question 6

What are the three types of virus shapes?

Answer 6

Icosahedral
Helical
Complex

Question 7

What is an icosahedral virus shape?

Answer 7

20 faces, each an equilateral triangle

Question 8

What is an helical virus shape?

Answer 8

Protein binds around DNA/RNA in a helical fashion

Question 9

What is an complex virus shape?

Answer 9

Neither helical or icosahedral

Question 10

How do viruses replicate?

Answer 10

Attachment
Penetration
Uncoating
Replication of genomic nucleic acid
Protein synthesis
Virion assembly (insertion of virus proteins into a membrane)
Budding and release

Question 11

What happens in the attachment stage of virus replication?

Answer 11

Viral proteins on the capsid or phospholipid envelope interact with specific receptors on the host cellular surface.

This specificity determines the host range (tropism) of a virus.

Question 12

What happens in the penetration stage of virus replication?

Answer 12

The process of attachment to a specific receptor can induce conformational changes in viral capsid proteins, or the lipid envelope, that results in the fusion of viral and cellular membranes. Some DNA viruses can also enter the host cell through receptor-mediated endocytosis.

Question 13

What happens in the unocating stage of virus replication?

Answer 13

The viral capsid is removed and degraded by viral enzymes or host enzymes releasing the viral genomic nucleic acid.

Question 14

What happens in the replication stage of virus replication?

Answer 14

After the viral genome has been uncoated, transcription or translation of the viral genome is initiated.

It is this stage of viral replication that differs greatly between DNA and RNA viruses and viruses with opposite nucleic acid polarity.

This process culminates in the de novo synthesis of viral proteins and genome.

Question 15

What happens in the assembly stage of virus replication?

Answer 15

After de novo synthesis of viral genome and proteins, viral proteins are packaged with newly replicated viral genome into new virions that are ready for release from the host cell.

This process can also be referred to as maturation.

Question 16

What are the two methods of virion release?

Answer 16

Lysis or budding

Question 17

What is the lysis method of virion release and what is an example?

Answer 17

Lysis results in the death of an infected host cell, these types of viruses are referred to as cytolytic.

An example is variola major also known as smallpox.

Question 18

What is the budding method of virion release?

Answer 18

Enveloped viruses, such as influenza A virus, are typically released from the host cell by budding.

It is this process that results in the acquisition of the viral phospholipid envelope. These types of virus do not usually kill the infected cell and are termed cytopathic viruses.

Question 19

What are the syndromes associated with viral infections?

Answer 19

Respiratory
Neurological
Gastroenteritis
Hepatitis
Skin infections
Eye infections
Congenital abnormalities
Arthralgia - infection of a joint
Lymphadenopathy (disease affecting the lymph nodes)

Question 20

What are the consequences of viral infection?

Answer 20

No, short or long lasting immunity

Chronic infection

Latent infection (lysogenic part of the cell cycle - lies dormant)

Transformation - long term infection with altered cellular gene expression

Question 21

Describe the status of the viral genome during latency

Answer 21

Retained in host cell - expression is restricted

Question 22

What is produced during viral latency?

Answer 22

Produces few antigen and no viral particles are produced

Question 23

What is viral latency?

Answer 23

Virus latency is the ability of a pathogenic virus to lie dormant within a cell

Question 24

What can does virus reactivation cause?

Answer 24

May or may not cause disease

Question 25

When is reactivation most likely to occur?

Answer 25

In the immunocompromisd - also where it is most severe

Question 26

How can some viral infections lead to cancer?

Answer 26

Modulation of cel cycle control - driving cell proliferation

Modulation of apoptosis - preventing programmed cell death

Reactive oxygen species mediated damage - infections can cause persistant inflammatory processes which lead to cancer via reactive oxygen species

Question 27

What are obligate intracellular pathogens?

Answer 27

Can only replicate inside a host cell

Viruses are these

Question 28

Define virion

Answer 28

The complete, infective form of a virus, outside its host cell, with a core RNA and a capsid

Question 29

What encapsulates the nucleic acid of a virus?

Answer 29

A protein capsid

Question 30

What encapsulates the nucleic acid of a virus?

Answer 30

A protein capsid

Question 31

What surrounds the protein capsid?

Answer 31

A lipid envelope containing spike projections

Question 32

What are the methods of viral transmission?

Answer 32

Blood bourne
Sexual
Vertical
Faecal - oral
Droplet
Airborne
Close contact
Vector-borne (indirect transmission of an infectious agent - occurs when a vector bites or touches a person
Zoonotic ( a disease that normally exists in animals but can infect humans)

Question 33

What might the coinfection of human and animal or bird strains in one organism lead to?

Answer 33

Recombination and generation of a new strain

Question 34

What are the three aspects of a virus that you can detect?

Answer 34

The whole organism - microscopy

Part of the organism (antigen, nucleic acid - PCR (extraction of genetic material followed by amplification of a specific region)

The immune response to a pathogen (used to determine a recent infection, prior infection or a response to vaccination)

Question 35

What is common in all antiviral agents?

Answer 35

They are virustatic none are virucidal.

This means they only inhibit the growth of the virus, stops the virus replicating

Question 36

Why are their limited target proteins for antiviral drugs?

Answer 36

Virus utilises host cell enzymes in order to replicate

Question 37

Give a reason why antiviral therapy is not used very commonly

Answer 37

Toxicity to the host cell is not uncommon

Question 38

Give examples of when antiviral therapy may be used

Answer 38

Prophyaxis (prevents infection)

Pre-emptive therapy (when evidence of infection is detected but symptoms are not yet apparent)

Overt disease

Suppressive therapy - keeps viral replication below the rate that causes tissue damage in asymptomatic infected patient, common in long term immunodeficiency patients.

Question 39

What are the possible methods of prevention of viral infections?

Answer 39

Immunisation
Prophylactic treatment post exposure
Infection prevention and control measures - isolation of symptomatic patients, PPE, Safe disposal of sharps
Screening blood, tissues and organs
Antenatal screening

Question 40

When can viruses be eradicated?

Answer 40

No animal reservoir or ability to amplify in the environment

Clearly identifiable in diagnosis

No chronic state carrier (so you don’t miss those who are infected)

Efficient and practical intervention

Political and social support

Question 41

What are antiviral therapy?

Answer 41

Antivirals are medications that help your body fight off certain viruses that can cause disease. Antiviral drugs are also preventive. They can protect you from getting viral infections or spreading a virus to others.

Question 42

What are the principles of anti viral therapy?

Answer 42

Virus Targets
Cellular targets
Viral Pathogenesis and Antiviral Strategy
Drug-Resistance Mutations
Pharmacodynamics

Question 43

What is a host range?

Answer 43

An inability of the virus to successfully adsorb and/or enter cells because of an incompatibility between virus capsid proteins (or virus envelope proteins ) and the host receptor molecule.