Apart from humans, their livestock, and the various monsters, the Nordics are also home to surviving wildlife, from the (probably entirely unaffected) plants to several species of mammals. The latter even occur in places that have seen the Illness and are still considered unsafe, so we may assume that their pre-Rash populations included a certain percentage of immune individuals as well.
Sweden and Norway Edit
Since the HQ of the cleansers is located in Mora, we may assume that the depicts actual Swedish post-Rash animals - moose and hares, to be precise - to illustrate the forests regrown on cleansed land.
In addition, we are beasts in the shape of wolves and small rodents and it is suggested that in general, rare healthy animals of the same species as the beasts are still in existence as well.
The comic has not yet shown any Danish places beyond the formerly Danish territory of Greater Copenhagen. We have seen (house) cats and (fallow) deer so far, which both are feral animals, not Y0 native fauna. They might qualify as part of the Y90 fauna, though.