Lecture 1

• What are the three theories for the origin of viruses?

  1. Viruses predated cellular life - viruses predated/ coevolved with current cellular hosts
  2. Cellular life came first- viruses arise from genetic elements that gained the ability to move between cells
  3. Viruses originated via regression or reductive process- viruses evolved from a more complex, free-living organism that over time lost genetic information and thus adapted a paracitic approach fro replication.
• viruses such as measles or smallpox appeared as human populations/communities grew
• What factors ensure continued virus survival?

  • the number of susceptible hosts available
  • How long humans live after initial infection
  • How the immune system responds
  • The time between infection and first symptom.
• what is the genetic conflict that transforms host and virus evolution?

  the interface between host proteins and viral proteins is constantly adapting. for host-virus conflicts to make a significant impact on the host, there needs to be a significant period of a common history.
• about 8% of the human genome is made up of ancient endogenous retroviruses (ERVs)
• Human endogenous retroviruses are often referred to as Junk DNA could have been responsible for antiviral resistance in early human ancestors.
• why have some HERV genes co-opted by their mammalian hosts?

  to mediate cell-cell fusion = multinucleate barrier

  Suppress maternal immunity

  Protects fetus from exogenous retroviruses
• The general life cycle of a virus?

  1. Attachment
  2. Penetration
  3. Uncoating
  4. Replication
  5. Assembly
  6. Release
• Basic physical properties of a virus?

  • Enveloped / non-enveloped
  • Capsid structure- icosahedral, helical, complex
  • Genome structure- RNA or DNA
  • viral proteins- Structural, non-structural
• What information is encoded in the viral genome?

  • Replication of the viral genome
  • regulation+ timing of the replication cycle
  • Modulation of host defenses
  • assembly and packaging of the genome
  • Ability to spread to other cells and hosts
• What is not encoded within the viral genome?

  no genes for...

  Complete protein synthesis

  Energy production

  no conventional centromeres
• All viral genomes must make mRNA that will be translated by host ribosomes
• What are the DNA virus groups?

  Group 1: +/- dsDNA goes straight into mRNA

  Group2: is + dsDNA which turns into +/-dsDNA then mRNA
• What are the RNA virus groups?

  Group 3: +/-RNA becomes mRNA

  Group 4: +RNA turns into -RNA then mRNA

  Group 5: -RNA will become mRNA
• What are the retro-transcribing viruses virus groups?

  Group 6: +RNA, reverse-transcription into DNA and then mRNA

  Group 7: +/-DNA turned into +RNA then reverse transcriptase into DNA then mRNA
• Why study viruses?

  Some cause disease

  can act as models for studying cellular processes

  can be used for biotechnology
• What is a risk group?


  the classification of organisms based on risk factors inherent to the organism:

  pathogenicity

  infectious dose

  mode of transmission

  host range

  available preventative measures

  available of effective treatment
• Risk assessment has to be considered.

  • potential aerosol generation
  • quantity/volumes
  • concentrations
  • stability in the environment
  • type of work proposed
• What is Risk Group 1?

  there is low individual and community risk.

  the biological agent is unlikely to cause disease in healthy humans and animals
• What is Risk Group 2?

  Moderate risk to the individual, but low community risk.

  any pathogen that can cause human disease but in normal circumstances, it is unlikely to be a serious hazard.
• What is Risk Group 3?

  high individual risk, low community risk

  any pathogen that will normally cause serious human disease or results in serious economic consequences but doesn't transmit casually from person to person
• What is Risk Group 4?

  any pathogen that usually produces serious human disease, which is often untreatable, and is readily transmitted. can be spread directly or indirectly
• what is a biosafety level?


  is the description of the minimum containment needed to handle organisms safely.
• What is a biosafety level 1?

  is a basic lab, has no special design features, biological cabinets are not needed, E.coli, infectious canine hepatitis.
• What is a biosafety level 2?

  Primary exposure risks are ingestion, inoculation, and mucosal membrane route. agents are not normally airborne. Need centrifuges, PPE, handwashing sinks, decontamination ( autoclaves)
• BSL 2 agents include:

  • All hepatitis
  • human herpes
  • influenza
  • Polio
  • pox viruses
  • measles
  • any human-derived blood, bodily fluid
  • HIV

  used for clinical specimens and non-culture procedures
• What is a biosafety level 3?

  also known as a BSL-2+

  will have a separate building, or isolated zone with double door access

  has directional airflow, room penetrations are sealed, and has enclosures for aerosols. SARs-CoV1/2, yellow fever, rabies
• What is a biosafety level 4?

  The max containment, agents could have:

  aerosol transmission

  low infectious dose

  produce serious/fatal diseas
• BSL4 facilities will have complete sealing of the perimeter with pressure decay testing

  Isolation of the researcher from the pathogen

  decontamination of air produced
• What are some BSL 4 viruses?

  Ebola

  Smallpox

  herpesB