An outbreak of Ebola in West Africa has been linked to the deaths of more than 120 people in Dakar Senegal, according to the latest World Health Organization count.

There is no vaccine and no cure for the deadly virus, and its appearance in West Africa, far from its usual sites in Central and East Africa, has caused some panic.

Health workers are trying to contain its spread, tracking down anyone with whom the sick have had contact. Mali announced on Tuesday that samples from all its suspected cases had tested negative for the disease.

Malian health minister Ousmane Kone said that the country had sent out 10 samples for testing at labs in the United States and Senegal, and all were declared negative for Ebola.

There are no other known suspected cases in the country. As of Monday, the UN health agency said it had recorded a total of 200 suspected or confirmed cases of Ebola, the majority of which are in Guinea.

That figure includes some of the Mali cases that the government now says are negative. The organization said the deaths of 121 people in Guinea and Liberia have been linked to the disease.

Officials have said the current outbreak could last months.