4.6.14 How ‘the evolutionary race’ between pathogens and their hosts has resulted in sophisticated invasion mechanisms

We have evolved a very effective immune system, consisting of barriers, non-speficif  defence mechanisms and specific ones. If we’re so good at fighting infections, why do we  still get ill?


Answer: pathogens are evolving as well. So how has TB evolved to beat us?

  1. It is spread by droplet infection, which is the most effective method of infection


  1. It specifically targets epithelial cells, which means that, when inhaled, it is exactly where it wants to be


  1. It does not kill immediately. This means that it has a large window of opportunity to spread to others


  1. It has a very thick waxy cell wall, which means it is partially protected against lysozyme


  1. It can survive inside macrophages and lie dormant until the immune system is weakened, when it can re-infect.

So how has HIV evolved to beat us?


  1. It weakens the immune system to increase its chance of survival


  1. It stays in the body for years, so it can spread


  1. It specifically targets Helper T cells


  1. It is spread by sexual contact, so it is easily spread