No one had any idea that yellow fever occurred in the Anglo-Egyptian Sudan until 1933, when its previous biological existence was discovered as part of an Africa-wide immunity survey conducted by the International Health Division (IHD) of the Rockefeller Foundation (RF). The IHD immunity test results baffled scientists and laymen alike: while the tests revealed pockets of high immunity to yellow fever in southern Sudan, the disease was clinically unknown in that area, indeed in all of East Africa, and no doctor could recall ever having seen a case. The discovery caused widespread consternation in the international political community, which feared that newly developing commercial air travel would spread the disease from East Africa to the virgin soil of Asia. For IHD it was an exciting, if medically puzzling, find. The Britishrun Sudan government was less enthused: only just climbing out of the Depression, it was compelled to assume the costs of compliance with international regulations designed to contain the spread of a disease which its doctors claimed did not exist in Sudan.