If donor area is effected by infection, does it lead to any dangerous things?

If you are worried about infection, you need to contact your doctor and have it looked at right away.  Faster you contact your doctor, the faster you can treat the problem.

Yes, if an infection goes untreated it can have some very serious consequences. If you suspect you  have one contact your doctor about it as soon as possible, or if you cannot contact them find another specialist who can help you.
However, numbness by itself is pretty normal following a transplant and if that is your only symptom then it is likely not an infection. Generally infections are signaled by redness, fever, drainage, and/or tenderness.

If your donor area is warm and red, or if there is drainage or unexpected pain, there could be an underlying infection.  If so this should be looked at right away.