The document discusses virology, which is the study of viruses. Viruses are ubiquitous and can infect all forms of cellular life, causing diseases ranging from mild like the common cold to lethal like AIDS. Virology is important for developing vaccines, drugs, and diagnostic tests. Viruses cause economic losses in agriculture and can be used for applications like phage typing in epidemiology, producing enzymes, and as antibacterial agents or gene vectors for treating diseases and producing proteins. Viruses have a capsid that surrounds their genome and some have an envelope. They are classified based on their structure and nucleic acid.

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