Oftentimes newly minted MDs will go to third world countries to practice where the need for medicine is most dire. But is this really a sensible way to help the suffering?
In the US, doctors can earn several hundred thousand a year just a few years out of their residency. In Africa they probably make little or nothing. So the question is whether doctors can help more people with their money than with their labor.
Undoubtedly there is need in Africa for oncologists, cardiologists, and other specialists, but the low-hanging fruit are the people who lack access to basic things like food, clean water, mosquito nets, vaccinations, etc. Of the people who do need urgent medical care, most of them probably suffer from the same ailments: aids, cholera, malnutrition, dysentery, etc. A dedicated nurse in Africa has much more experience diagnosing and treating these things than does your average graduate from Johns Hopkins.
Presumably Africa has less restrictive laws on who can practice medicine, and the cost to educate and train a medical worker in Africa is much lower. Their knowledge of local languages and customs will likely make them much better nurses and doctors for the region, too. Do we really need our doctors overseas giving routine vaccinations to people who are inclined not to trust them? Wouldn't it make more sense to finance an army of African doctors and nurses?
Rather than go to Africa after medical school and residency, our best and brightest should try to make as much money as they can in the US. If they are really such angels (and I hope they are), they will use their earning potential here to help the neediest abroad. If you're willing to work for nothing in Africa, why not make a half million a year here and send $400k to Africa to train nurses, fund hospitals, supply aid, etc?
In Africa, your labor is worth less and your money is worth than it is in the US. So this is a great opportunity for arbitrage: work here, send your money there. Giving Africans your labor instead of your money just doesn't make sense.