The number of people believed to be infected with the deadly Ebola virus has surpassed 15,300, the World Health Organization (WHO) says.

According to the latest WHO figures released on Friday, the death toll in the Ebola epidemic has currently increased to 5,459 out of 15,351 cases identified in a total of eight countries since the outbreak started in West Africa late last year.

While the rate of transmission in Guinea and Liberia has slowed, Sierra Leone is still reporting a high incidence of transmission, the WHO added.

Meanwhile, UN Secretary General Ban Ki-moon expressed concerns over the spread of Ebola in the African sate of Mali and announced that the international body was expanding its Ebola emergency mission to the country in a bid to prevent further outbreaks.

"Decisive national action combined with international support today will help to prevent a spread of the outbreak in Mali to crisis proportions tomorrow,” he said.

The UN chief further called on the international community “to stay engaged” to help “contain and end the outbreak by the middle of next year."

David Nabarro, UN special envoy on Ebola, also noted that a total of USD 1.5 billion was required through next March to fight the epidemic.

Ebola is a form of hemorrhagic fever with symptoms such as diarrhea, vomiting, and bleeding.

The virus spreads through direct contact with infected blood, feces or sweat. It can be also spread through sexual contact or the unprotected handling of contaminated corpses.