If you're interested in global and/or public health, an MPH before an MD would make more sense and, honestly, be regarded more highly in the medical profession than an MSN. There are no shortcuts for medical school (idk if that's what you were alluding to). Many PAs, NPs, and CRNAs (including the current president of ASA) have made changes into the medical careers. They all completed the same 4years of med school and same residencies as kids straight out of college. Any previous nursing experience might help your application or make some topics/clinical situations more familiar. But at is the extent of "credit" nursing will earn you towards medicine.
In fact, you will probably need at least 2 years of pre-reqs just to meet minimum admission requirements for med schools
. Chemistry and possibly other coursework for BSNs are generally not at the level med schools are looking for and sometimes even looked down upon.
Nursing and medicine, while overlapping and sharing a great deal of knowledge base, are entirely different professions and there are no more educational shortcuts than any two other professions.