Families hiding infected loved ones and the existence of "shadow zones" where medics cannot go mean the West African Ebola epidemic is even bigger than thought, the World Health Organization said on Friday.
Some 1,427 people have died among 2,615 known cases of the deadly virus in West Africa since the outbreak was first identified in March, according to new figures released by the WHO on Friday.
However the U.N. agency, which has faced criticism that it moved too slowly to contain the outbreak, said that many cases had probably gone unreported.
Despite initial assertions by regional health officials that the virus had been contained in its early stages, Ebola case numbers and deaths have ballooned in recent months as the outbreak has spread from its initial epicentre in Guinea.
"We think six to nine months is a reasonable estimate," Keiji Fukuda, the WHO's Assistant Director-General for Health Security, said during a visit to Liberia, speaking of the time the agency now believes will be required to halt the epidemic.
An Ebola outbreak will be declared over in a country if two incubation periods, or 42 days in total, have passed without any confirmed case, a WHO spokesperson said.