Producing a disease called Ebola fever, this virus was first documented in July 1976 when it struck a small village in Sudan. Victims became fevered and began to bleed, much as they do with Lassa fever. Ebola killed half the people it infected. In September it struck again, in Zaire, seemingly more virulent than before. Sweeping through more than 50 villages, it killed 90 percent of its victims. To prevent an explosive epidemic in the capital city, Kinshasa, the Zairean government sealed off all roads into the afflicted area.
Ebola and Marburg Hemorrhagic Fevers, deadly viral diseases characterized by massive bleeding and destruction of internal tissues. The closely related Ebola and Marburg viruses can be highly contagious through contact with infected bodily fluids. Both diseases have high fatality rates and together have caused more than 1,500 deaths in parts of Africa since the 1970s. Ebola virus is named for the Ebola River in the Democratic Republic of the Congo, where the virus was first identified in 1976. Marburg virus is named for Marburg, Germany, where the virus was isolated in 1967 after an outbreak among laboratory workers who came in contact with body parts of African monkeys. As well as affecting humans, Ebola has killed large numbers of gorillas and chimpanzees in some areas of Africa.
The animal hosts of the viruses remain largely unknown, but evidence points to the role of fruit bats as possible natural hosts (called reservoir hosts) of Ebola virus. Infected bats did not show clinical signs of infection, but carried the virus, viral RNA, and antibodies against the virus. Otherwise, the life cycles of both viruses are still mysterious—we do not know how the viruses jump from reservoir hosts to humans.
From the index case, transmission of virus between humans occurs by direct contact with infected blood or other body fluids, usually involving health-care personnel and family members caring for sick patients. Transmission of Ebola virus has also occurred by handling ill or d*ad infected chimpanzees
Wild chimpanzee populations are also threatened by the Ebola virus, a deadly type of hemorrhagic fever that can infect humans. Ebola outbreaks in parts of West Africa are thought to have killed large numbers of chimpanzees since the mid-1990s, but exact figures have not been established. (Ebola is estimated to have killed more than 5,000 gorillas in the region.) Some outbreaks of Ebola among humans have been linked to contact with wild chimpanzees. Other research indicates that the human immunodeficiency virus (HIV) that causes acquired immunodeficiency syndrome (AIDS) likely developed from a chimpanzee retrovirus that infected people. The retrovirus then underwent mutations in humans, resulting in HIV. Research published in 1999 showed that HIV spread from chimpanzees to humans on at least three separate occasions in Central Africa, probably beginning in the 1940s or 1950s. Chimpanzees infected with the original retrovirus or with HIV do not develop AIDS, however.
The deadly Ebola virus has emerged as a new threat to gorillas. In late 2006 scientists reported that more than 5,000 gorillas in the Republic of Congo and in Gabon di*d from Ebola outbreaks from 2002 to 2004. The virus causes a hemorrhagic fever that can result in massive internal and external bleeding. Ebola can be spread by contact with bodily fluids and has killed more than 1,200 humans in Africa since 1976. Fruit bats are known to harbor the virus and may somehow have infected the apes, who then spread the disease among themselves. The virus combined with the hunting of gorillas for the bush-meat trade could threaten some gorilla populations with extinction.
The incubation period for Ebola and Marburg virus infection—that is, the time between exposure and the onset of illness—is typically four to ten days and is followed by abrupt onset of severe headache, fever, chills, sore throat, muscle aches, and weakness. These early symptoms are followed by vomiting, abdominal pain, diarrhea, and conjunctivitis (inflammation of the mucous membranes in the eye). There is usually bleeding from body openings and a rash, and evidence of abnormal blood-clotting that is associated with profound shock. Death often follows quickly, usually six to nine days after clinical onset of the disease. In a pregnant woman, abortion is a common consequence of infection, and when women who are dying of infection give birth, their infants invariably die. Convalescence is slow and marked by physical weakness, weight loss, and often by amnesia for the period of acute illness.