Ebola - the killer virus 

Ebola Haemorrhagic Fever is one of the most virulent viral disease known to humankind, causing death in 50-90% of all clinically-ill cases. This frightening and highly contagious disease causes its victims to bleed to death. The disease has its origins in the jungles of Africa and Asia and several different forms of Ebola virus have been identified and may be associated with other clinical expressions, on which further research is required.

The Congo strain of the virus is the most deadly to date, proving fatal in just under 90% of those who contracted. 

History
The Ebola virus was first identified in a western equatorial province of Sudan and in a nearby region of Congo Kinshasa (DRC) in 1976 after significant epidemics in Yamkubu, northern DRC, and Nzara, southern Sudan. Between June and November 1976 the Ebola virus infected 284 people in Sudan, with 117 deaths. In the DRC there were 318 cases and 280 deaths in September and October. An isolated case occurred in the DRC in 1977, a second outbreak in Sudan in 1979. In 1989 and 1990, a filovirus, named Ebola-Reston, was isolated in monkeys being held in quarantine in a laboratory in Reston (Virginia), Alice (Texas) and Pennsylvania. In the Philippines, Ebola-Reston infections occurred in the quarantine area for monkeys intended for exportation, near Manila. 

A large epidemic occurred in Kikwit, DRC in 1995 with 315 cases, 244 with fatal outcomes. One human case of Ebola haemorrhagic fever and several cases in chimpanzees were confirmed in Côte d'Ivoire in 1994-95. In Gabon, Ebola haemorrhagic fever was first documented in 1994 and recent outbreaks occurred in February 1996 and July 1996. In all, nearly 1,100 cases with 793 deaths have been documented since the virus was discovered. The natural reservoir of the Ebola virus seems to reside in the rain forests of Africa and Asia but has not yet been identified.

The latest greater outbreak of Ebola reported is in the Northern Uganda district of Gulu in October 2000. Gulu is located close to both Southern Sudan and Eastern DRC. At least 33 people have died and a total of 62 people are known to have contracted the disease but doctors fear that many in remote villages may have died before they could get medical help. 

Different hypotheses have been developed to try to uncover the cycle of Ebola. Initially, rodents were suspected, as is the case with Lassa Fever whose reservoir is a wild rodent (Mastomys). Another hypothesis is that a plant virus may have caused the infection of vertebrates. Laboratory observation has shown that bats experimentally infected with Ebola do not die and this has raised speculation that these mammals may play a role in maintaining the virus in the tropical forest.

The disease
The Ebola Haemorrhagic Fever is a highly contagious disease, which causes its victims to bleed to death. Ebola is often characterised by the sudden onset of fever, weakness, muscle pain, headache and sore throat. This is followed by vomiting, diarrhea, rash, limited kidney and liver functions, and both internal and external bleeding. Eventually, this can cause enough blood loss to cause shock and respiratory problems, leading quickly in many cases to death. 

The Ebola virus is transmitted by direct contact with the blood, secretions, organs or semen of infected persons. Transmission through semen may occur up to 7 weeks after clinical recovery, as with Marburg haemorrhagic fever. Transmission of the Ebola virus has also occurred by handling ill or dead infected chimpanzees, as it has been documented in Côte d'Ivoire. Health care workers have frequently been infected while attending patients. In the 1976 epidemic in the DRC, every Ebola case caused by contaminated syringes and needles died. 

Suspected cases normally are isolated from other hospital patients and strict barrier nursing techniques are practiced. Patients who die from the disease have to be promptly buried or cremated.

Treatment 
No specific treatment or vaccine exists for Ebola haemorrhagic fever. Severe cases require intensive supportive care, as patients are frequently dehydrated and in need of intravenous fluids. Experimental studies involving the use of hyperimmune sera on animals so far have demonstrated no long-term protection against the disease after interruption of therapy. However, scientists are still working on the development of vaccinations against Ebola, and recent studies show that these may be working on laboratory animals. There are also promising signs of the development of some therapies that can be used on victims. 

Much of the scientific work underway is focused on finding the original source of the disease, the reservoir. The natural reservoir of the Ebola virus is still not known. Extensive ecological studies are currently under way in Côte d'Ivoire, Gabon and the DRC to identify the reservoir and the animals which originally hosted the virus. Finding the reservoir of the virus would help understand how it works and thus ease the efforts to find a cure or a vaccine.

Sources: Based on WHO

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