Explained: How do viruses move from animals into humans?

From the bubonic plague to the COVID-19 pandemic, humans are vulnerable to a host of viral invaders that can jump ship from their original host species. Viruses do so by either acquiring new mutations or swapping genetic material with another virus, which enables them to enter human cells, evade immune surveillance, and cause an infection. With rapid globalization and habitat loss forcing closer human-wildlife interactions, understanding zoonic viral transfer is increasingly pertinent.