Pathogen evasion case studies

• HIV impact on immune system

  1. HIV attacks white blood cells with CD4 receptors (e.g., helper T cells)

  2. HIV enters the cell, replicates itself, kills the cell, and finds other cells with CD4 receptors to restart the cycle
• Influenza antigenic variation


  1. Antigenic shift

  2. Antigenic drift
• Antigenic variation in influenza leads to the need for new flu vaccines every year
• Dengue immune system enhancement

  Antibodies against dengue virus enhance the rate of infection
• Pathogens

  • Can evade the immune system using 3 strategies: Antigenic variation, Attack on the immune system, Latency
• Dengue characteristics

  Enveloped RNA virus with 1 single-stranded, positive-sense RNA
• HIV latency consequences

  When the rate of helper T cell destruction exceeds the host's capacity to replenish them, cell-mediated immunity falters, leading to Acquired Immunodeficiency Syndrome (AIDS)
• Dengue antigenic variation


  Uses antigenic variation strategy with 4 well-studied strains or serotypes
• HIV latency strategy


  1. During clinical latency, some virus particles and helper T cells are destroyed and replenished as rounds of virus replication take place

  2. Some HIV proviruses remain latent if activated infected helper T cells return to resting state
• Dengue immune system attack

  Attacks monocytes, dendritic cells, and macrophages
• Antigenic shift

  • Due to gene reassortment or direct transmission from one species to another
  • Radical changes in antigen
  • Abrupt and sudden
  • Occurs occasionally
  • May give rise to pandemics
• Antigenic drift

  • Due to mutation
  • Smaller changes in antigen
  • Gradual accumulation of mutations
  • Occurs frequently
  • May give rise to epidemics