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?
- It is spread by droplet infection, which is the most effective method of infection
- It specifically targets epithelial cells, which means that, when inhaled, it is exactly where it wants to be
- It does not kill immediately. This means that it has a large window of opportunity to spread to others
- It has a very thick waxy cell wall, which means it is partially protected against lysozyme
- 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?
- It weakens the immune system to increase its chance of survival
- It stays in the body for years, so it can spread
- It specifically targets Helper T cells
- It is spread by sexual contact, so it is easily spread