I think some of the reasons not much exploration is done outside the known world are:
*fuel,most of the reserves are probably still in infected area's or reserved for the military
*climate,from the evidence so far trolls don't do very well in cold environments
*own survival,setting up ounce own survival environment & increasing the environment in which it is safe is preferable in taken on extra survivors
Places where other survivors could be
Northern Hemisphere
*Hebrides
*Faroes
*Shetlands
*Greenland
*Isle of Man
*Artic
Southern Hemisphere
*Fireland (a island at the southern tip of South America,separated by the Magellan strait)
*Falklands (if Argentina didn't invade after the collapse of the UK government)
*St-George(if Argentina didn't invade after the collapse of the UK government)
*Tasmania
*New Zeeland(if they managed to isolate quick enough)
*Antartica
Other places
*Luna (well far fledged idea)
So far we've seen that all mammals except for those in the feline branch (this includes tigers,ect...) are susceptible to the pathogen.
Avian & reptilian seem to be immune.
And since Iceland seems to be still infection free almost a 100 years on I think this pathogen can't survive in salt water.
Also I suspect their might be plants that got infected/mutated in the past 9 decades to further spread the disease