Ebola virus (EBV), also known as Ebola hemorrhagic fever, is a zoonotic disease which carries a case fatality rate of up to 90 percent. Symptoms of Ebola virus emerge after a one to two week incubation period with infected individuals developing fever, diarrhea, vomiting, respiratory disorders, and hemorrhaging from numerous sites.
Since the first recorded outbreak in 1976 in Yambuku, Democratic Republic of the Congo (formerly Zaire), a number of other outbreaks have occurred and isolates of those affected during these events have led to the identification of five types -- the most recent of which has been identified during the latest outbreak in Bundibugyo District, Uganda, in 2007.
The name of the virus is derived from the river Ebola (which flows in the vicinity of Yambuku) and as is evident below, the types of the Ebola viruses are named after the respective regions in which their outbreaks first occurred:
- Zaire Ebolavirus, 1976
- Sudan Ebolavirus, 1976
- Reston Ebolavirus, 1989
- Ivory Coast Ebolavirus (aka Taï Forest Ebolavirus), 1994
- Bundibugyo Ebolavirus, 2007
With the exception of the Reston ebolavirus (which does not have human pathogenicity), all other types have resulted in human infection.
What continues to baffle researchers is the identification of a natural reservoir. According to Feldmann et al (2004) because of past efforts to identify a reservoir, it can be assumed that the reservoir is either a rare species or that transmission within the reservoir species itself is less efficient. Indeed, though bat species remain the strongest candidates, no infectious Ebola virus has yet been isolated from non-human animals despite substantial sampling from a number of species at outbreak sites.
The lack of a known natural reservoir has made it particularly challenging to prevent outbreaks. Fortunately however, its rare appearance, minimal spread (as of 2006, ~1000 cases have occurred), as well as the remote locations of outbreaks in the past have limited widespread mortality. Despite the fact that these same factors may not ignite interest in the development of a vaccine (from an economical perspective), concerns over the potential that the virus may be utilized as a medium for bio-terrorism has been supporting the drive for creating a vaccine. While a number of vaccines have shown efficacy in conferring resistance in other species, there remains no FDA approved human vaccine currently.
See part 2 of this post to learn what researchers are discovering today about Ebola.
- The natural history of Ebola virus in Africa (NCBI, 2055)
- Key Protein May Give Ebola Virus Its Opening (New York Times, 2012)
- Ebola virus entry requires the cholesterol transporter Niemann—Pick C1(Nature, 2011)
- A nonreplicating subunit vaccine protects mice against lethal Ebola virus challenge (PNAS 2011)