Can manual labour for 7+ years lead to arthritis in the hands and fingers?

No. In colorado, the worker's compensation board has made the determination that osteoarthritis of the hand is not caused by work. There is differences in each state how they agree/disagree with this. In general, degenerative arthritis (wear and tear type) is from a lifelone accumulation of stress, and has genetic predisposition as well. Arthritis is not brought on by most labor jobs.