From the infamous Black Death to the 1918 flu to COVID-19, disease outbreaks have always marked human history.

But where they spread, how they spread, and how fast they move have all changed. As humans became more mobile, started trading goods and information across the globe, built bigger cities, increased their greenhouse gas emissions, and had more contact with wildlife and farm animals, disease began to spread easier and faster than ever before. At the same time, humans got better at preventing and combating outbreaks. But no prevention or treatment is perfect for every disease. When new outbreaks occur, people have to work together to figure out what causes the disease, how to prevent its spread, and how to treat it.