Bangladesh, Oct. 23 -- Eincluding two where it's active. It has spread farther across Africa than any previous Ebola outbreak, reaching three regions.

Nigeria on Tuesday became the latest country affected by the outbreak, which was first declared in eastern Congo in mid-May. Caused by the rare Bundibugyo virus for which there's no approved vaccine or drug, the outbreak has killed at least 4,600 of the 9,500 people infected in Congo.

The World Health Organization has said it is the fastest-growing outbreak of Ebola in history. In Africa, it's been recorded in the central, western and eastern regions.

A recurring problem in the spread in Africa is what appears to be lax surveillance efforts as most of the first cases were confirmed long ...