DAKAR, Senegal - The number of people believed sickened by Ebola has passed 10,000, according to figures released Saturday by the World Health Organization, as the outbreak continues to spread.

The Ebola epidemic in West Africa is the largest outbreak of the disease ever with a rapidly rising death toll in Guinea, Liberia and Sierra Leone. There have also been cases in three other West African countries, Spain and the United States.

The UN health agency said Saturday that the number of confirmed, probable and suspected cases has risen to 10,141. Of those, 4,922 people have died. Those figures show about 200 new cases since the last report, four days ago.

Even those grisly tolls are likely an underestimate, WHO has warned, as many people in the hardest hit countries have been unable or too frightened to seek medical care. A shortage of labs capable of handling potentially infected blood samples has also made it difficult to track the outbreak. For example, the latest numbers show no change in Liberia's case toll, suggesting the numbers may be lagging behind reality.

On Thursday, authorities confirmed that the disease had spread to Mali, the sixth West African country affected, and a new case, in a doctor recently returned from Guinea, was confirmed the same day in New York.