The implication is that the jotnar was patient zero for the rabies outbreak and infected all the other trolls. So how did a solitary troll living in Arctic mountains above the snow line get infected with rabies, let alone an enormous animal that has no natural predators? Norway has officially been rabies-free since the nineteenth century. Did somebody do it deliberately with an agenda?
An infected animal such as a wolf or a bat that got in from the Russian border could have infected the jotnar.
Considering the end of the film states that none of the teenagers were ever seen again, it's likely that Thomas never got to a hospital. Good luck with that rabies treatment.
That's assuming that they weren't just outright killed by the Norwegian government.
Given that Thomas already appeared to be showing symptoms of rabies getting help would have done very little, anyway.
Just where did Hans get that bucket of Christian men's blood?
Since he's a government agent, he probably has the resources (or knows someone with the resources) to get it from a blood bank.
A blood bank would seem like an unlikely source, since they don't generally ask the religion of the donor. Someone working within the TSS could have easily given it just for this purpose, though.
Blood banks do keep records of the donors' names and personal details. It's established the TSS are government-funded, so they could look for a donor's name in census listings and work out which were Christians.
When told how trolls in fairy tales act like people, Hans immediately says that fairy tales are for kids and don't necessarily conform to reality. Well of course trolls would act like people in fairy tales and be wild beasts in real life; fairy tales also portray animals as sapient, when they really aren't, so why should trolls be an exception?