That was my first thought, but this line:

>His body was hot to the touch and he sweated heavily, he constantly had foul body odour [...]

suggests an fantastically high baseline metabolism.

Makes me think of DNP, a substance which acts to dissipate the protein gradient in our mitochondria, wasting the energy that the mitochondrion would otherwise use to make ATP. The wasted energy is turned into heat, giving its users an elevated body temperature and characteristic sweating. It'd be the perfect dieting aid were it not so toxic.

There are proteins in the human body having the same effect, performing some minor functions. Maybe he had a mutation making those proteins very prevalent, essentially making his metabolism very wasteful. Although I don't know if such a sustained fever wouldn't be deadly.

https://en.wikipedia.org/wiki/2,4-Dinitrophenol https://en.wikipedia.org/wiki/Uncoupling_protein

DNP has a particularly vile reputation in the fitness community, yet many still use it.