More than 1,900 people have died from the Ebola virus during the current outbreak, according to new figures released Wednesday by the World Health Organization, or WHO. The death toll from this outbreak is now greater than all previous outbreaks combined.

The organization confirmed that over 3,500 people in Guinea, Sierra Leone and Liberia have been infected during the outbreak. The WHO fears 20,000 people could be infected.

WHO head Margaret Chan described the outbreak as “the largest and most severe and most complex we have ever seen," according to BBC News

"No one, even outbreak responders with experience dating back to 1976, to 1995, people that were directly involved with those outbreaks, none of them have ever seen anything like it."

Dr. Tom Frieden, director of the CDC, said that the official figures underestimate the actual number of cases because families afraid of the stigma associated with Ebola don't report sick loved ones. Others are caring for patients in isolation, according to CNN

United Nations officials said that the pace of the outbreak has accelerated, with close to 400 deaths in the past week alone. 

There are fears that the pace of the outbreak may increase further still, after a doctor in Nigeria continued to treat patients after developing symptoms of Ebola and may have exposed scores of people to the virus, according to the Los Angeles Times. Nigeria, Africa's most populous country, has thus far avoided the heavy caseloads that its neighbors have endured.

The Ebola virus was first identified in 1976, when the first major outbreak of the disease occurred. There was a second major outbreak in 1995. Both were in West Africa. According to the WHO, Ebola outbreaks have a case fatality rate of up to 90 percent.