Virology

1
Virology
2
Properties of Viruses

• Contain a single type of nucleic acid, either DNA
  or RNA, not both. The DNA and RNA can either be
  double stranded (ds) or single stranded (ss)
  depending upon the virus.
• Surrounded by a protein coat called a capsid.
• Capsids made up of smaller units called
  capsomeres.
• Some are enveloped, meaning that the capsid is
  surrounded by another layer made up of lipids,
  proteins, and carbohydrates.
• Only animal viruses have envelopes. Animal
  viruses are viruses capable of infecting humans
  as opposed to phages, which infect bacteria.

3

• Some enveloped viruses may be covered in
  spikes. Spikes are protein or carbohydrate
  complexes used for attachment to the target cell.
• Spikes can mutate and then the virus can reinfect
  the same individual. Influenzavirus is an example
  of a virus that does this.
• Viruses multiply inside living cells using cell
  machinery to replicate nucleic acid and make
  proteins.
• Viruses cause synthesis of specialized structures
  that can transfer viral nucleic acid to other
  cells

4
General Morphology

• There are some general shapes that animal viruses
  tend to have.
• Helical see figure 6.5 for a great description
  of this structure.
• Polyhedral has multiple sides. An example of a
  polyhedral shape is icosahedral.
• Complex virus this is a virus that does not fit
  into one of the above categories. An example of
  this kind of virus would be a bacteriophage

5

• Virion A virion is a complete, fully developed,
  infectious viral particle.
• Host Range Each virus has a different host
  range. The host range is the number of different
  host cells a virus can infect.
• The attachment proteins on the outside of the
  virus determine the host range for a virus. If
  they are compatible with proteins on the host
  cell membrane found on many cells then the host
  range will be large. If the viral proteins are
  only compatible with a protein found on a few
  host cell membranes then the host range will be
  small.

6
Cultivation

• Since viruses are obligate intracellular
  pathogens tissue cultures have to be grown in
  order to cultivate viral particles.
• Tissue cultures are started with small tissue
  samples of organs that viruses are known to
  infect, such as kidney or lung cells.
• Primary cell line The initial tissue sample
  that is used to start a tissue culture, derived
  from tissue slices is called the primary cell
  line.
• Generally tissue samples last only a few
  generations.

7

• Continuous cell lines transformed, or altered,
  cells (cancerous) can be maintained through an
  indefinite number of generations. Essentially a
  cancerous cell is one in which the programmed
  cell death response has been turned off. The cell
  will grow and divide indefinitely.
• Cytopathic effect When tissue cultures are
  grown, the cells grow in a single layer, called a
  monolayer, on the bottom of a plastic flask.
  When the tissue monolayer is infected with a
  virus it will cause cell deterioration. The
  changes in the appearance of the cells and the
  monolayer as a whole are called cytopathic
  effects. The changes in the cells and monolayer
  can be used for diagnosis for some viruses
  because they will create a distinct change.
• For example, RSV (respiratory syncytial virus)
  causes the infected cells to join together
  forming large cells with many nuclei.

8
Multiplication of Animal Viruses

• Use Fig. 6.11 in your textbook.
• 1. Attachment (adsorption) attachment proteins
  on the virus attach to receptor sites on host
  cells.
• Attachment is complete when multiple sites have
  been bound by viral particles.
• 2. Penetration endocytosis or fusion with
  plasma membrane. The virus is engulfed into the
  cell.
• 3. Uncoating separation of viral nucleic acid
  from capsid (and envelope if the virus has an
  envelope).
• Controlled by enzymes inside the host cell or
  inside the virus itself.

9

• 4. Biosynthesis of DNA viruses replication of
  DNA in nucleus of host cell using host enzymes
• Synthesize capsid and other viral components in
  cytoplasm using host cell enzymes
• 5. Assembly capsid is formed and the nucleic
  acid is inserted.
• 6. Release cell is lysed and virions are free.
• Enveloped viruses will push through the membrane
  instead of breaking the cell open. The host cell
  membrane contains viral protein spikes that then
  surround the virion when it pushes through the
  membrane.

10
Viral Classification

• Viruses grouped into families, subgroups, and
  genera.
• -viridaefamily
• -virinaesubgroup
• -virusgenus
• Example
• Parvoviridae (family)
• Parvovirinae (subgroup)
• Parvovirus (genus)
• Erythrovirus (genus)

11

• Viruses are grouped into families according to 3
  things
• 1)  Nucleic Acid (ds or ss RNA, ds or ss DNA)
• 2)  Morphology of virion
• 3) Strategy of viral replication
• For example retroviruses use RNA as a template to
  make DNA. This process is called reverse
  transcription.
• Reverse transcription is used by HIV.

12
DNA Virus Families and Diseases

• Adenovirus cause of common cold
• Poxviridae smallpox, cowpox
• Herpesviridae cold sores (HHV-1)
• Genital herpes (HHV-2)
• Chickenpox (HHV-3 or varicella zoster)
• Papovaviridae papillomavirus warts
• Hepadnaviridae cause Hepatitis B

13
RNA Virus Families and Diseases

• Picornaviridae causes polio
• Togaviridae West Nile Encephalitis
• Rhabdoviridae rabies
• Reoviridae cause respiratory and intestinal
  tract infections
• Retroviridae HIV