2. General Virology
Concept of virology
Types of viruses
Size and Shape
3. Concept of Virology
• Virology is the bioscience for study of
viral nature, and the relationship
between virus and host.
• Viruses often cause serious diseases,
relate to some cancers and congenital
deformities, also can be used as tool for
4. Definition of Virus
Viruses may be defined as acellular organisms
whose genomes consist of nucleic acid protected
by the protein coat, and which obligately
replicate inside host cells and too small to be seen
by electron microscopy.
L. Pasteur in 1884 and A. Mayer in 1886
• Studied on mosaic disease of Tobacco plant/ transformation of disease
D. Iwanowsky in 1892
• Studied on extract from tobacco plant suffering from mosaic disease.
M. Beijernick in 1898
• Disease causing filterable viruses multiply in host
F. Twort and F.d herelle
• Some viruses infect bacteria called bacteriophage
W. Stanley in 1935
• Demonstrate the structure of plant virus that was Tobacco Mosaic Virus
6. Viral Properties/ Characteristics
• Viruses are inert (nucleoprotein ) filterable
• Viruses are obligate intracellular parasites
• Viruses cannot make energy or proteins
independent of a host cell
• Viral genome are RNA or DNA but not both.
• Viruses have a naked capsid or envelope with
• Viruses do not have the genetic capability to
multiply by division.
• Viruses are non-living entities
7. Consequences of Viral Properties
• Viruses are non living out side the cell
• Viruses are disease causing agent
• Viruses must be able to use host cell processes to
produce their components (viral messenger RNA,
protein, and identical copies of the genome)
• Viral components must self-assemble
• The fully assembled infective particle is called
8. Challenges the way we define life
• viruses do not respire,
• they do not move
• they do not grow
• they do most certainly reproduce, and may adapt
to new hosts.
9. Types Of Viruses
• cause disease in man and animals.
• Contain DNA core covered by capsid.
•cause disease in plants.
•Contain RNA core covered by
28. Viral core
• Viral core
The viral nucleic acid genome, In the
center of the virus.
Control the viral heredity and variation,
responsible for the infectivity.
• The genome of a virus can be either DNA or RNA
• DNA-double stranded (ds): linear or circular
Single stranded (ss) : linear or circular
• RNA- ss: segmented or non-segmented
ds: linear (only reovirus family)-not circular
32. Viral Capsid
• The protein shell, or coat, that encloses
the nucleic acid genome.
• a. Protect the viral nucleic acid.
• b. Participate in the viral infection.
• c. Share the antigenicity
•The core of a virus particle
consisting of the genome plus
a complex of proteins.
• complex of proteins = Structural proteins
+Non- Structural proteins (Enzymes &
Nucleic acid binding proteins)
38. Cubicor icosahedral symmetry
• Cubic or icosahedral symmetry
• Identical 20 triangularunits arranged in cluster of five or
six, 12 corner and 30 edges
• covered with capsomeres
• Mostly spherical shaped
• Including animal virus
42. Example of Icosahedral
2. Hepatitis Virus
Hepatitis A Virus (HAV)
Hepatitis B Virus (HBV)
Hepatitis C Virus (HCV)
Hepatitis Delta Virus (HDV)
Hepatitis E Virus (HEV)
3. Herpes Virus
Herpes Simplex Virus 1 (HHV1)
Herpes Simplex Virus 2 (HHV2)
4. Human Immunodeficiency
5. Human T-lymphotrophic
6. Polio virus
8. Rubella Virus
43. Complex Virus Structures
• Uncertain symmetry
• Proteins and lipoproteins
• A well known example is the tailed
• The head of these viruses is cubic with
a triangulation number of 7. This is
attached by a collar to a contractile tail
with base plate and tail fibril
48. Properties of naked viruses
• Stable in hostile environment
• Not damaged by drying, acid, detergent, and heat
• Released by lysis of host cells
• Can sustain in dry environment
• Can infect the GI (gastrointestinal tract) and
survive in the acid condition
• Can spread easily via hands, dust, fomites, etc
• Can stay dry and still retain infectivity
• Neutralizing mucosal and systemic antibodies are
needed to control the establishment of infection
•A lipid-containing membrane that
surrounds some viral particles.
• It is acquired during viral maturation by a
budding process through a cellular
membrane, Viruses-encoded glycoproteins
are exposed on the surface of the envelope.
• Not all viruses have the envelope, and
viruses can be divided into 2 kinds:
enveloped virus and naked virus.
53. Functions of envelope
some viruses possess
neuraminidase (The enzyme helps
viruses to be released from a host
55. Properties of enveloped viruses
• Labile in dry , arid environment
• Damaged by drying, acid, detergent,
• Pick up new cell membrane during
• Insert new virus-specific proteins after
• Virus is released by budding
56. Consequences of Properties for
• Must stay moist
• Must not infect the GI tract for survival
• Must be transmitted by droplets, secretions,
blood and body fluids
• Must re-infect another host cell to sustain
• Humoral and cell-mediated immunity are
needed to control the infection
59. Spike or Peplomer
A peplomer is a glycoprotein spike on a viral capsid or
viral envelope. These protrusions will only bind to certain
receptors on the host cell, they are essential for viral
•Viroids are small (200-400nt), circular
RNA molecules with a rod-like
secondary structure which possess no
capsid or envelope which are associated
with certain plant diseases. Their
replication strategy like that of viruses -
they are obligate intracellular parasites.
• Viroids are small (200-400nt), circular RNA
molecules with a rod-like secondary structure
which possess no capsid or envelope which are
associated with certain plant diseases. Their
replication strategy like that of viruses - they are
obligate intracellular parasites.
• Prions are rather ill-defined infectious agents
believed to consist of a single type of protein
molecule with no nucleic acid component.
Confusion arises from the fact that the prion
protein & the gene which encodes it are also found
in normal 'uninfected' cells. These agents are
associated with diseases such as Creutzfeldt-Jakob
disease in humans, scrapie in sheep & bovine
spongiform encephalopathy (BSE) in cattle.
Notas do Editor
Humoral Immunity - this involves the use of antibodies produced by the b cells to attack any invading foreign bodies like bacteria, viruses etc. Production of memory cells also takes place for a faster response in case of a second infection.Cell mediated immunity- this involves the destruction of self cells damaged by mutations or infected by viruses. this form of immunity includes cells like cytotoxic t cells nk cells.