Member of the virus
, classified as a level 4 pathogen
has an incubation period
of two to twenty-one days and has a 70 to 90% mortality rate
. The virus made its first appearance in 1976
in the area of Yambuku
, Zaire, spread mainly by contaminated needles
used in local hospitals
. 318 people contracted the virus, and 88% of them died.
Ebola-Zaire has made several appearances since 1976. After a long absence, it showed up again in Gabon in 1994, once more in Zaire (now known as the Democratic Republic of the Congo) in 1995, twice more in Gabon in 1996, and once in South Africa in 1996.
Ebola-Zaire holds the distinction of being the most lethal subtype of the Ebola virus. Its origin remains unknown, however the virus can be spread to humans by some species of bats and by monkeys. Surprisingly, samples of Ebola-Zaire taken in 1976 are virtually identical to samples taken in 1995 and 1996, showing that the virus did not mutate for 18 years. In addition to the time difference, the outbreaks occurred more than 1,000 kilometers away from each other. This is intriguing, since filoviruses naturally tend toward genetic divergence.
The fact that Ebola-Zaire spent 18 years in hiding without mutating despite traveling a great distance has led researchers to believe that the virus lies dormant in an animal (or animals) that are very widespread or migratory throughout Africa. The four different strains of Ebola are genetically diverse by as much as 45%, which suggests that the viruses are carried by more than one species.