Biodiversity loss, which is both exacerbated by and feeds into climate change, has lead to a "pandemic era". 335 new infectious diseases have emerged in recent decades.

There are four typical venues for spillover events: habitat loss, extreme weather events, vector expansion (vectors being mosquitos, ticks, rats, etc. Expansion happens by removal of predators and expansion of tropics), and CAFO (concentrated animal feeding operations, i.e. factory farms).