The World Health Organization (WHO) says the death toll from the Ebola outbreak in West Africa has reached 518.

The international body said on Tuesday that 50 new cases, half of them fatal, were reported by officials in Guinea, Liberia and Sierra Leone from July 3-6.

The UN health agency also noted that the overall number of laboratory-confirmed, probable or suspected cases of the illness in the region has jumped to 844.

Guinea is the worst-hit country with 408 cases and 307 deaths. Liberia’s health officials announced 16 new cases and nine deaths that brought the tally to 131 cases and 84 deaths.

Sierra Leone also reported 34 new cases and 14 deaths, taking its overall count to 305 cases and 127 fatalities.

There is currently no known cure for Ebola, a form of hemorrhagic fever whose symptoms are diarrhea, vomiting and bleeding.

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

Ebola was first discovered in the Democratic Republic of Congo in 1976 in an outbreak that killed 280 people.

It remains one of the world’s most virulent diseases, which kills between 25 to 90 percent of those who fall sick.