DAKAR, Senegal — Health officials say the Ebola outbreak in West Africa could last for months in what they called one of the most challenging episodes of the disease that the international community has faced.

Dr. Keiji Fukuda of the World Health Organization said Tuesday that the current outbreak is especially difficult because of the wide area over which it has spread — extending from Guinea's tropical forests to its capital and over the border into Liberia. But officials also emphasized that they have traced the source of transmission in every sick person, an important step in controlling the disease.

More than 100 deaths have been linked to the virus since the outbreak began last month.

Fukuda said he expected the outbreak to continue for another two to four months.