Pandemonium

When a pandemic ensues, it disrupts the very lives of the people causing a number of negative events: crime, domestic violence, looting and distrust of neighbor, family and friends as most people don't know how to combat the 'Menace' that goes berserk and, with a voracious appetite devours the crops, harvests, trees, and when they-re gone-eventually to wooded houses-and people.
When the mighty rainforests are devoured by the Menace, the whole ecosystem and biodiversity of the world changes: There are mega droughts, superstorms, flooding beyond belief-and other catastrophic events that humankind is unable to deal with: and-less oxygen-slowly decimating humankind to the next mass extinction.