In a crazy time such as the apocalypse, there are many humans who want to save themselves from being killed and found by the Horsemen that are occupying the different continents, so, many people try to make deals with the only people that are able to 'guarentee' them safety. Demons.
As a result of this deal, the demon rarely keeps it's promise and begins to drain the human that he has made the pact with, eventually turning them into a form of servant to the demon itself, rather than the free human that you were supposed to be once you'd made the deal.
Eventually these cursed humans begin to develop into lesser demons themselves as their soul is changed by their closeness to the demon that has enslaved them, due to the large numbers of demons in the South American Continent there are also a large number of cursed humans in those regions also.
If you would like to play a cursed human, it would be useful to try and contact a Demon in order to set up someone you can become faithful to