Virology notes

1. Virology
• The study of viruses
• Very ubiquitous
• Infect all cellular life forms
• Manifestation of diseases in host
organisms
• Many viruses and their effects still to
be discovered

2. Importance of viruses
• Disease-causing agents
• Viral diseases range from the non-lethal,
such as common colds, to the lethal, such as
rabies, AIDS and Covid
• Virology is important to develop vaccines,
diagnostic tests and anti-viral drugs
• Small pox has almost been eradicated by
vaccination while AIDS can be managed by
antiretroviral drugs

3. Importance of viruses cont’d
• Disease-causing agents cont’d
• Economic losses due to diseases
in livestock and plants
• Rice yellow mottle virus
• Cucumber mosaic virus
• Viruses can attack bacteria used
in the food industry for
fermentation

4. Importance of viruses cont’d
• Phage typing
• The identification of bacterial strains on the basis of the viruses that
attack them
• Important in epidemiology to identify sources of outbreaks
• Enzymes
• Reverse transcriptase are obtained from retroviruses
• RNA polymerases are obtained from phages

5. Importance of viruses cont’d
• Anti-bacterial agents
• Viruses which attack bacterial cells are used as anti-bacterial agents
• Emergence of anti-biotic resistant strains has increased interest in
phages
• Anti-cancer agents
• Genetically modified viruses are being trialed as anti-cancer agents
• Herpes simplex and vaccinia viruses

6. Importance of viruses cont’d
• Gene vectors for protein production
• Viruses are used as vectors to take specific genes into target cells
• Genetically modified cells are then used to mass produce proteins,
such as growth hormone and insulin
• Gene vectors for treatment of genetic disorders
• Viruses can be used to insert a non-mutated gene to treat a genetic
disease
• Severe Combined Immunodeficiency has been treated by introducing
a normal gene in stems cells via retroviruses

7. Viral structure
• A virion is a complete, fully
developed, infectious viral particle
composed of nucleic acid and
surrounded by a protein coat
outside a host cell
• Viruses are classified by their
nucleic acid or structure of
protein coat/capsid

8. Viral genomes

9. Viral capsid and envelope
• A protein coat that encircles the
viral genome is called a capsid
• Each capsid is composed of protein
units called capsomeres
• Capsomeres can be of a single type
on a virus and can be of different
types
• The arrangement of capsomeres is
characteristic of a specific virus

10. Viral capsid and envelope cont’d
• In some viruses, the capsid is
covered by an envelope made
up of lipids, proteins and
carbohydrates
• Some membranes have spikes
(coronavirus) while others do
not have
• Spikes are commonly used to
attached to host cells
• Viruses without an envelope are
called non-enveloped viruses

11. Viral capsid and envelope cont’d
• Antibodies are produced by host
cells to inactivate viruses and stop
an infection
• Some viruses can escape immune
response because the gene for
surface/spikes is susceptible to
mutations
• The influenza virus gene for spikes
rapidly mutates, a reason why
people are infected over again

12. Capsid structure
• Helical viruses
• Resemble long rods, which may
be rigid or flexible
• The genome is located inside a
hollow, cylindrical capsid that has
a helical structure
• The Ebola hemorrhagic fever virus
is a typical example

13. Capsid structure cont’d
• Polyhedral viruses
• Are many-sided viruses
• Most are icosahedron, a regular polyhedron
with 20 triangular faces and 12 corners
• Adenovirus and poliovirus are typical
examples

14. Capsid structure cont’d
• Spherical viruses
• Capsid is roughly spherical
• Most spherical viruses are
enveloped
• The influenza virus is
typically spherical and
enveloped

15. Capsid structure cont’d
• Complex viruses
• Have complicated capsid shapes
• Bacteriophages are typical
examples, with a polyhedral head
and a tail
• The head contains the nucleic
acid while the tail performs other
functions, such as attachment to
host cells