Emerging viral diseases are often the product of a host shift, where a pathogen jumps from its original host into a novel species. Studies have shown that host shifts are a common in the evolution of most pathogens, but why pathogens can successfully jump between some host species but not others is only just becoming clear. The susceptibility of potential new hosts can vary enormously, with close relatives of the natural host typically being the most susceptible. Often, pathogens must adapt to successfully infect a novel host, for example by evolving to use different cell surface receptors, to escape the immune response, or to ensure they are transmitted by the new host. If you’d like to read more about host shifts in the scientific literature, these review articles are a good place to start: here and here.

If you are interested in how pathogens spread, and why they cause harm, you could look at this other excellent TED-Ed video on how germs spread and how they make us sick.

For some of the issues around predicting the next big epidemic in humans you could read this article.

We have developed a game called Viruscraft that is based on research about host shifts – you play as a virus and have to add receptors to a virus to help it spread both within and between species.

For more on the ubiquity of viruses and viral epidemics in a pop-science format see “A Planet of Viruses” by Carl Zimmer

For an overview of the research we’ve carried out on host shifts using an insect-virus model system see this website.