Introduction to viruses Flashcards
What was the first virus identified?
Yellow fever virus
When was small pox introduced?
16th century to distinguish from great pox aka syphilis
What causes smallpox?
variola virus
What kind of virus is variola virus?
A poxvirus
What is so significant about smallpox?
It was the first disease successfully eradicated by vaccination
How many people did Spanish Flu kill?
> 50 million people
Why is it difficult to control pandemic influenza?
New strains continuously emerging
What cancer was HIV associated with?
Kaposi’s sarcoma
Are new emergences of viruses rare events?
No, new viruses emerge regularly
What is MERS?
Middle East Respiratory Syndrome, a new coronavirus disease that emerged in 2012 and by 2015 it had disseminated to 27 different countries
How fatal is MERS?
Fatal in 50% of infected
What was the origin of MERS?
Camel to human transmission
What is the host range of viruses determined by?
Virus requirements for attachment to host cell
Availability of host cell factors required by virus to replicate
Ability of virus to evade host defences
Can viruses cross species barriers?
Yes and they frequently do
How does mode of infection determine clinical outcome?
The cells which can be infected will determine what is damaged. (Eg. HIV attaches to CD4 so it can only infect CD4 T cells)
How does influenza virus A infect people?
It attaches to sialic acid on epithelial cells
What is the structure of a virus?
3 main parts:
Nucleic acid (DNA or RNA)
Protein coat (capsid)
Lipid membrane (envelope)
Are all viruses enveloped?
No
What is a virion?
A single virus particle
Infectious and fully developed
What type of structures can the viral nucleic acids be?
DNA or RNA
Single or double stranded
Linear or circular
Can be segmented
Size ranges from a few thousand nt to 250k or more
How many nts can giant viruses have?
1m+
What are some examples of giant viruses?
Mimivirus
Pandoravirus
What is a capsid?
A protein coat that surrounds the nucleic acid
What is the capsid used for?
It is a vehicle for transport and proteiction
What makes up most of the mass of the virus?
The capsid
What is a capsid made up of?
Repeated subunits called capsomeres.
What are capsomeres made up of?
Single or several protein types. Arrangement is characteristic for the particular virus
What are the types of viral morphologies that are possible?
Helical viruses
Icosahedral viruses
Complex
What are helical viruses like structurally?
Rigid or flexible
Nucleic acid within hollow cylindrical, helical capsid
Spiral arrangement of capsomers around nucleic acid
What are some examples of helical viruses?
Ebola
Influenza
When was helical symmetry of viruses first described?
1955 by Fraenkal, Conrat and Williams
How are icosahedral viruses formed?
Capsomers assemble into 20 equilateral triangular faces
What can regular complex viruses look like?
Capsids can have both helical and icosahedral symmetry.
Additional structures can also be present such as the capsid (polyhedral) and the sheath (helical)
Think of bacteriophages to understand this better
What can irregular complex viruses look like?
Non-symmetrical capsid structure (eg pox viruses)
They lack clearly identifiable capsids
Several coats can be present around the nucleic acids
What can envelope of virus be used for?
To group viruses
What are viral envelopes made of?
Outer lipid membrane derived from host membrane and contains viral proteins.
What does the viral envelope do?
Mediates viral attachment to host cells for cell entry
What structures do enveloped viruses usually have?
Helical or icosahedral
How are viruses seen?
EM
How small are viruses?
100 times smaller than a single bacterial cell
What did mimivirus resemble when it was first discovered?
Gram positive bacteria residing within amoeba
How does sputnik replicate itself if it cannot replicate in acanthamoeba by itself?
It uses the machinery of another virus called mamvirus to replicate itself.
What are the ways viruses are classified?
Orders (-virales)
Families (-viridae)
Genera (-virus)
Species
How are viruses grouped into families?
Morphology
Nucleic acid type (RNA or DNA)
Strategy of replication
What are the criteria for grouping viruses into genera?
Primary criteria:
Significant differences in genome sequence
Minor difference in genome structure
Type species: virus which has all the properties characteristic of a certain genus
What are the criteria for grouping viruses into a certain species?
Separate species associated with serological differences, genomic differences, and structural + physical properties.
What is a species when talking about viruses?
Defined as class of viruses with many properties that constitutes a replicating lineage and occupies a particular ecological niche
How are new species of virus created?
Variant species arise as a result of minor mutations in genome
How are species subgrouped?
Subtypes
Clades
Strains
Variants
Quasispecies
What are prions?
Non-viral proteins that cause disease. (eg spongiform encephalopathy)
What diseases are caused by prions?
Chronic wasting disease in deer
Mad cow disease
Cruetzfeldt-Jakob disease in humans (vCJD)
Kuru - first identifiable spongiform encephalopathy
Where are prions typically located?
In nervous tissue
What do prions do?
Convert glycoprotein PrP(c) to PrP(Sc) [misfolds the protein]
How is mad cow disease transmissible?
Surgical instruments
Orally: via consumption of infected meat/nervous tissue
