What is bone marrow depression? any treatment for this?

Mostly not needed: any illness, espcially mild colds, can do this on a very temporary basis. also malnutrtion, or anything that causes weight loss. These are easily fixable. Can be from cancer or serious organ failure. Mostly it isn't.

Depends: What you are implying. The bone marrow produces various cells of the blood and each has its role and each lack has specific manifestations. total bone marrow aplasia means all the cell lines are low. treatment varies upon etiology and the particularly affected cells