Introduction to Viruses Flashcards
What can viruses be classified as?
Viron/symmetry
Presence or absence of envelope
Genome structure
Mode of replication
What is a viral culture?
A test to find viruses that can cause an infection.
What makes a viral culture positive?
If the cells show changes, known as cytopathic effects, then the culture is positive.
Describe shell vial culture
The sample is centrifuged onto a single layer of cells and viral growth is measured by antigen detection methods
List human virus infections of major importance
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
What are the three types of virus shapes?
Icosahedral
Helical
Complex
What is an icosahedral virus shape?
20 faces, each an equilateral triangle
What is an helical virus shape?
Protein binds around DNA/RNA in a helical fashion
What is an complex virus shape?
Neither helical or icosahedral
How do viruses replicate?
Attachment
Penetration
Uncoating
Replication of genomic nucleic acid
Protein synthesis
Virion assembly (insertion of virus proteins into a membrane)
Budding and release
What happens in the attachment stage of virus replication?
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.
What happens in the penetration stage of virus replication?
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.
What happens in the unocating stage of virus replication?
The viral capsid is removed and degraded by viral enzymes or host enzymes releasing the viral genomic nucleic acid.
What happens in the replication stage of virus replication?
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.
What happens in the assembly stage of virus replication?
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.
What are the two methods of virion release?
Lysis or budding
What is the lysis method of virion release and what is an example?
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.
What is the budding method of virion release?
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.
What are the syndromes associated with viral infections?
Respiratory
Neurological
Gastroenteritis
Hepatitis
Skin infections
Eye infections
Congenital abnormalities
Arthralgia - infection of a joint
Lymphadenopathy (disease affecting the lymph nodes)
What are the consequences of viral infection?
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
Describe the status of the viral genome during latency
Retained in host cell - expression is restricted
What is produced during viral latency?
Produces few antigen and no viral particles are produced
What is viral latency?
Virus latency is the ability of a pathogenic virus to lie dormant within a cell
What can does virus reactivation cause?
May or may not cause disease
When is reactivation most likely to occur?
In the immunocompromisd - also where it is most severe
How can some viral infections lead to cancer?
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
What are obligate intracellular pathogens?
Can only replicate inside a host cell
Viruses are these
Define virion
The complete, infective form of a virus, outside its host cell, with a core RNA and a capsid
What encapsulates the nucleic acid of a virus?
A protein capsid
What encapsulates the nucleic acid of a virus?
A protein capsid
What surrounds the protein capsid?
A lipid envelope containing spike projections
What are the methods of viral transmission?
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)
What might the coinfection of human and animal or bird strains in one organism lead to?
Recombination and generation of a new strain
What are the three aspects of a virus that you can detect?
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)
What is common in all antiviral agents?
They are virustatic none are virucidal.
This means they only inhibit the growth of the virus, stops the virus replicating
Why are their limited target proteins for antiviral drugs?
Virus utilises host cell enzymes in order to replicate
Give a reason why antiviral therapy is not used very commonly
Toxicity to the host cell is not uncommon
Give examples of when antiviral therapy may be used
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.
What are the possible methods of prevention of viral infections?
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
When can viruses be eradicated?
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
What are antiviral therapy?
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.
What are the principles of anti viral therapy?
Virus Targets
Cellular targets
Viral Pathogenesis and Antiviral Strategy
Drug-Resistance Mutations
Pharmacodynamics
What is a host range?
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.
