Viruses Flashcards
What is a virus?
“An infectious, obligate Intracellular parasite comprising Nucleic acids (DNA or RNA) surrounded by a protective protein coat an/ or a protective envelope derived from a host cell membrane”
What are viruses made up of?
All viruses contain:
Protein
Nucleic acid
Some viruses contain:
Glycoproteins
Lipids (membrane)
Describe DNA containing viruses
They are very diverse
Range in size from 3600 bases to 2.5 million bases
Can be single or double stranded
Can be linear or circular
Describe RNA containing viruses
Also diverse
Range in size from 1700 bases to 32000 bases
Can be single stranded or double stranded
Can be linear, segmented or circular
What are the 6 key stages to the viral replication cycle?
- Attachment
- Penetration
- Uncoating
4a. Transcription of viral genomes b. Translation of early genes - Assembly
- Release
Describe attachment
Vast majority of viruses sue specific receptors n cells to gain entry into them
Absorption leads to an attachment of a virion to a host cell
Define adsorption
Process of cell coming into contact with virus
List the 3 different types of tropism
Cellular
Tissue
Host
Describe penetration
Process of membrane fusing with receptor mediated endocytosis
The lipid membrane of viruses fuses to lipid membrane of a host
Describe uncoating
The release of Nucleic acid and enzymes
Describe the transcription of viral genes
DNA viruses are transcribed via DNA dependent RNA polymerases
RNA viruses are transcribed using viral enzymes encoded by the genome carried in the virion
For retroviruses the RNA gene is copied first to DNA using reverse transcriptase followed by the host enzyme transcribing the viral DNA
+ve sense and ssRNA virus gene acts like mRNA to be transcribed
Describe the translation of early genes
Cellular ribosomes translate viral mRNA
Control proteins bind to host DNA
DNA and RNA replication enzymes are used if they’re encoded for
Describe translation of late genes
Genes for capsomeres and envelope proteins
Describe assembly
Each virus has a unique assembly pathway
If the virus is enveloped it requires both lipid envelope and envelope glycoproteins
When the Golgi apparatus and Endoplasmic reticulum become important
Describe the release process
Also known as egress
When the viruses leave the host cell
Some viruses are cytopathic whilst other are non-cytopathic
Describe the difference between cytopathic and non-cytopathic viral cells
Cytopathic cells will damage the cell that it replicates in rather than non-cytopathic cells will migrate from host cells through the body
Give the two phases that viruses can obtain
Extracellular- dead phase
Intracellular- Alive in a host cell
List the different vial transmission routes in humans
- Respiratory
- Faecal-oral
- Sexual contact
- Blood borne
- Vertical (mother to child)
- Human- arthropod- human
List the methods of viral transmission in zoonoses
- Vertebrate- vertebrate
- Vertebrate reservoir
List the basic approaches to developing a vaccine
- Whole inactivated virus
- Live attenuated virus
- Synthetic peptides
- Recombinant subunit
- Viral DNA or RNA
- Recombinant bacterial vectors
- Recombinant viral vectors
List the outcomes of natural viral infection
Asymptomatic- Immune system handles the virus
Acute infection- small symptoms occur but they are resolved quickly
Immunological resolve- life long (chronic) infection
Detrimental immunity
Cancer
Latent infection
Death
What is antiviral therapy?
Drugs used to treat viral infections
Give the 3 types of antiviral drugs and how they work
Non-specific antivirals- Intefer with viral replication
Direct- acting- Target specific steps in the life cycle of viruses
Indirect-acting- Often target host pathways
How are viruses inactivated to be made into a vaccine and why is this helpful?
By adding non-ionic chemical detergents
They inactivate a viruses infectivity but retain their antigenicity
How can DNA vaccines be used?
To make cells produce certain antigens
What are the 2 types of responses that occur when the immune system detects a virus?
Innate response
Adaptive response
List the innate immune cells and their function
Cytokines- Allow cell to communicate with each other
Natural killer cells- Recognises part of the infected cells and go in and kill them
Macrophages- phagocytose and sterilise ‘foreign’ substances
List the cells involved in the adaptive immune response and their function
B cells- Produce lots of antibodies
T cells:
Cytotoxic T cells- Recognise viral nested cells
T helper cells- Ensures all other components of immune system are best they can be
Regulatory T cell- Control immune activation ad allow it to be switched off when infection is cleared
Give 2 emerging viruses
Nipah Virus
Lassa Fever
Give 2 viral diseases and an effect they have on the body
Poliovirus pathogenesis- Virus replication in the cells of the anterior horn of the CNS that leads to tissue damage and eventual muscle paralysis
COV2- Causes cardiac and respiratory impairment,muscle fatigue and loss of taste and smell
