Beginnings Of Virology Flashcards
Where do infectious diseases rank in world wide number of cause of death?
Place 2, number 1 is cardiovascular diseases
Which six diseases cause 90 % of infectious disease deaths?
Pneumonia, tuberculosis, diarrhoeal diseases, malaria, measlees, HIV (and Sars Cov2)
What is the abiogenesis theory and how was it disproven?
Life forms spontaneously out of unenlivend matter (maggots in rotting meat) — disproven by Pasteurs Swan neck bottle
Against which viral diseases where the first vaccines developed?
Human Pox (Variola), Rabies
What did Robert Koch establish?
-Animal model: Anthrax pathogen from cattle to guinea pig
-Systematic approach
-Transparent artificial culture media
What are the principles of the Koch-Henleschen Postulate?
- Pathogen must be detectable in all diseased animals, not in healthy ones (problematisch in Viren: persistente/latente Infektionen)
- cultivating pathogen in pure culture (not possible with Kochs Method)
- pathogen can reproduce disease in healthy individuals (Problematic in viruses, long incubation period)
- Pathogen can be reisolated from newly diseased animals
Is it possible to cultivate viruses with the methods of Robert Koch?
No
What was a crucial technique to cultivate viruses? (to fullfill kochs postulates)
Ceramic filter — bacteria can be separated
Virus is stopped by fine grain Kitasto filter — no toxid fluid = virus concept
What are the first described viruses? And which virus is the first HUMAN virus identified?
NON HUMAN:
Tobacco Mosaic Virus (not filterable)
Foot and mouth disease virus
HUMAN
Yellow fever virus (Flavivirus)
Where is yellow fever found? What is the route of transmission? What vaccine is used?
-In tropical regions transmitted by mosquito (=vector) but no transmission from patient to patient
-Vaccine: attenuation in chicken embryo cell culture (17 D)
Why is it easier to isolate bacteria than viruses?
Viruses are submicroscopial genetic parasites which need the cellular system of the host for their replication –> identification of a permissive (animal) host needed
They are obligate intracellular — effective cell culture systems required
What are the problems of animals as model organisms for viral diseases? What is the solution?
Ethics
Costs
Hazards
Space requirements
Reproducibility
SOLUTION: working with cells instead of whole organisms
Eukaryotic cell cultures: What are primary cell cultures and permanent cell cultures and what is the advanatge?
Primary: cells directly from an animal — passages — dedifferentiation and dying after only a few passages
Permanent: use of tumor cells from patients or artificial tumor cells
How can cells be artificially immortalised?
-Tumor virus
-Chemical/ physical noxa
-Genetechnical manipulation
What are the requirements for effecient cell culture techniques?
-Sterile working
-Antibiotics
-Culture medium
-Immortalisation
-Growth factors (undefinded ingedients: serum, plasma, lymph, extracts of embryos; defined: factors produced by industry)
What are the characteristics of the polio virus?
Transmission between human host and animal host is possible
Live ettenuated vaccine in HeLa cells
what are the characteristics of a virus?
-infectious
-very small parasites
-obligate intracellular
-viral genome (DNA or RNA)
-genome replicated in suitable host cell
-new viruses generated de novo in host cell
what do viruses lack?
-protein translation apparatus
-own enegergy generation
what are always the components of a virus?
-nucleic acid
-capsid
what is the capsid?
protein layer encoded by virus
what facultative components of a virus are there?
-envelope (protein)
-lipid membrane
what is the simplest way to arrange identical protein subunits? What defines the structure? And which form does the virus have?
helix –> helical virus
defined by amplitude and pitch
is the virus morphology a good parameter for defining a virus?
no, because it is very diverse
What are the criteria for classification of a virus?
-Type of nucleic acid for the genome
-existence of an envelope
-symmetry of the capsid (helical, icosahedral)
-arragement of genes
-replication strategy
which criteria concerning the classification of viruses regarding the nucleic acids are used?
-DNA, RNA
-size
-single stranded, double stranded
-linear, circular, segmented
what are not criterias to classify viruses?
-host range
-pathogenicity and kind of disease
how many viruses classes are there according to the baltimore schema?
I-VII
How is the ICTV nomenclature structured? (important for exam)
order: virales
family: viridae
genus: virus
species: name
whose genome is bigger: RNA virus or DNA virus? Why?
DNA virus, because the RNA polymerase has no proofreading function (no stability in sequence)
What types of subviral infectious agents are there?
Virosoids
Viroids
Prions
what are the characteristics of virusoids? Name one example
encode proteins but not capsid proteins, they are helper dependent viruses (the virusoid-nucelic-acid is packaged by the capsid proteins of the helper virus)
e.g.: Hepatitis delta virus
what are the characteristics of viroids?
infectious RNA, encodes no proteins, capsid or envelopes at all
RNA is self complementary and forms rod shaped stabile structures
infect plants
what are prions?
infectious proteins, but no nucleic acid
which prion diseases are known?
Creutzfeldt_jakob
Scrapie
BSE
chronic wasting disease
How can virus infection be detected in a cell culture?
cytopathic effect
development of inclusion bodies
hemadsorption
what are the steps of the viral replicative cycle?
adsorption
penetration
replication
generation of new particles
release by cell lysis (virus burst)
How can viruses be counted?
addition of dilution series on tissue culture cell
counting of plaques in the monolayer
how can a biologically cloned virus be isolated?
covering the cell culture with agar
local cell lysis
viral progeny is locally fixed/stained
isolate plaque with pipette
which assays can be used to quantify viruses?
-plaque assay (quantifies only infectious particles)
-focus assay
-EM
-Pock assay (Pock formation)
-Hemagglutinin assay
how can cytolytic and non-cytolytic viruses be counted?
lytic: plaque forming units
non-lytic: focus forming units (dye reaction)
what is the difference between polyclonal antibodies and monoclonal anitbodies?
polyclonal: wide reactivity, low specificity
monoclonal: high range of reactivity, high specificity (one epitope)
what are ambisense genomes?
ssRNA: genome and antigenome or coding
Which viruses replicate via reverse transcription?
L+RNA (Retroviridae like HIV)
C-ss/ds DNA (Hepadnaviridae like HBV)
Define primary cell culture and cell line
primary cell culture: culture of cells from original tissue cultivated in vitro for the first time (not immortal but can be sub-cultured or gworn into strains)
cell line: immortal cell cultures (spontaneous or induced)
How does the plaque assay work?
Ability of a single infectious viral particle to form a macroscopical, cytopathic effect in a monolayer of cultivated cells
