it is 2087 and 62 years ago, a massive Parasitic Plague, which was named 'PTW-KA', which stands for "Plague That Will Kill All", the current population is a bit over 600 million, the Parasite infects any living thing by going into its digestive system and turning them into a gooey mess of a Zombie like creature

You are inside an abandoned building and you hear rustling upstairs, is it a Parasite or a Human