A more correct title would be "Bill and Melinda Gates Are Paying Off Nigeria's Polio Related $76M Debt to Japan." So Bill Gates wants to eradicate polio and has been funding countries. In this Japan loaned it to Nigeria and Bill Gates paid it off.
Paying debts for third world countries (is this still politically correct?) is not efficient, might as well give it directly to their leaders--you save on fees. A corrupt to the core, third world country would issue even more debt to buy votes with projects (after taking a 20% "fee" for the leaders,) hire more of their supporters in state jobs etc etc.