Viral Infections Flashcards
8% of our genome is made up of viral fragments and is adapted into human DNA.
True
Viruses adapt to live permanently within their host within a parasitic relationship.
True
Which came first, viruses or cells?
No one knows!
But cells are there to support the lives of the viruses.
Viruses existed in a pre-cellular world and played a key role in generating complex life via gene transfer (plasmid sequences between cells)
Describe Schmallenberg Virus
(“narrow mountain”)
Unlikely to cause disease in humans
- An animal disease which causes birth defects and miscarriages in livestock (sheep, goats, cattle)
- First emerged in 2011 (Germany, Netherlands)
•
- Symptoms in adult cattle include reduced milk yield and diarrhoea
- Causes late abortions and birth deformities in newborn sheep, goats and cattle.
- The virus is spread by midges, and has crossed the Channel from the continent.
SARS COV 2
ZOONOTIC - passed from animals to humans and vice versa.
Mutations create a change in the viral genome and changes the proteins to make it bind to ACE2 receptors (all over the body but primarily in the resp system).
Previously bound to bat receptors and mutated to be able to bind to human receptors.
Degree of severity depends on the number of ACE receptors.
Closely related to SARS COV (75-80%)
Emerged as a mutation.
Human to human transmission.
What is a virus?
Virus means POSION or TOXIN
It is a SMALL infectious agent (25-300nm) and cannot be seen under a regular microscope. Can see under an electron microscope.
A bacteria is larger (0.2-2um)
CANNOT grow outside of a host cell (is classed therefore as intracellular)
It can “survive” in the environment (eg on a door handle).
Shapes are characteristic of different types of virus.
See slide with pics on
What are the essential components of a virion?
Essential components of the virion:
¨Nucleic Acid – DNA or RNA, single or double stranded, one piece or several fragments (a segmented genome), linear or circular, of greatly varying size and type.
Capsid (protein) – usually made of blocks called capsomers
What are the OPTIONAL structures within a virus?
¨Envelope – usually obtained from the host cell and made of lipid. They push through the lipid bilayer and coat themselves with the plasma membrane.
Eg COVID is an envelope virus and the spike sticks out through the membrane.
Surface structures – e.g. “knobs”, apical fibres.
Enzymes – some viruses carry genes for enzymes required for their own replication e.g. HIV They carry a code to make their own virus or they carry one with them (RnA to DNA) so it can then integrate itself into the host cells. Infects t-lymphocytes and then the DNA integrates into the t-cell genome.
What does the protein matrix do?
Hemagglutinin binds to the host cell
LABEL the influenza virus….
The matrix protein allows proteins to enter the virus and allows it to release into the cytosol.
What does ICTV do?
The International Committee for the Taxonomy of Viruses (ICTV)
Classify viruses with a set of criteria:
nPrimary Criteria¨Which nucleic acid is present?¨Double or single stranded¨Presence/absence of envelopenSecondary Criteria¨Host(s) affected¨Capsid shape
Endings of taxons set as¨Order (-virales)¨Family (-viridae)nSubfamily (-virinae)nGenus (-virus)nSpecies (-virus)
See the Virusphere 2005 for genotypes
Name some DNA Viruses
(can integrate into genome and mutate heavily)
Herpes
Adeno
Papilloma
Epstein-Barr
Can be vaccinated and the vaccine does not need to be changed as the virus does not mutate.
Name some RNA viruses
(variety of acute serious infections)
¨Influenza¨Rotavirus¨Norovirus¨Coronavirus¨HIV¨Ebola¨Rabies
Difficult to come up with a vaccine as they mutate regularly.
Unusually high mutation rate.
Seasonal epidemics with flu, covid.
Where do viruses come from?
Mutation of existing viruses (RNA viruses).
Sudden spread from isolated populations (eg HIV in the 1980’s). No ability to sequence the genomes until the mid-80’s.
Spread from other animals.
Reservoirs of viral agents
Other people - most importance.
Animals - more important in other countries in comparison to the UK (east asia where they live in close proximity of livestock).
Environment - door handles, soil, oceans.
(Many bacteria are yet to be discovered int he oceans)
