The Bubonic plague slowed urbanisation, industrial development and economic growth in Europe for many years.
Despite being so small they can't be seen with the naked eye, pathogens that cause human disease have greatly affected the way humans live for centuries.
Just as organisms that infect us make changes in us - we too make changes in them and they grow and adapt to their human hosts.
Humans play host to many little passengers. Right now, you’re incubating, shedding or have already been colonised by viral, bacterial, parasitic or fungal microorganisms - perhaps even all of them.
It’s the ability of our immune system to remember past infections, and pass this memory on to our kids, that allows us to survive infectious diseases.
With so many microbes capable of hijacking and destroying us, how are we, as a species, still enduring?
Spanish flu killed more people than the Great War that preceded it. And tuberculosis even more than that.
Here we explore our past and present struggles with four of the most significant infectious diseases human beings have faced, and some of the progress we've made in prevention and treatment.