well, it depends upon the degree you received in Nigeria and the classes you took. Medical Schools WILL take people with a foreign undergrad degree, they look closer then at the classes and grades AND you MUST do well on the MCAT.
You CAN call each med school. Ask to speak to an admissions counselor who specializes in foreign students. Or you can email them. You don't most often have to get a degree in the US. You may have to go back and retake some science classes. Not anywhere near 60 hours worth.
good luck!