Ebola Haemorrhagic Fever

WHO Fact Sheet 103 Revised September 1997

Ebola Haemorrhagic Fever is one of the most virulent viral disease known to humankind, causing death in 50-90% of all clinically-ill cases. 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.

Transmission
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 was recently documented in Côte d'Ivoire. Health care workers have frequently been infected while attending patients. In the 1976 epidemic in Zaire, every Ebola case caused by contaminated syringes and needles died.

Incubation
2 to 21 days.

Symptoms
Ebola is often characterised by the sudden onset of fever, weakness, muscle pain, headache and sore throat. This is followed by vomiting, diarrhoea, rash, limited kidney and liver functions, and both internal and external bleeding.

Diagnosis:
Specialized laboratory tests on blood specimens (which are not commercially available) detect specific antigens or antibodies and/or isolate the virus. These tests present an extreme biohazard and are only conducted under maximum containment conditions.

Therapy:
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 demonstrated no long-term protection against the disease after interruption of therapy.

Containment
Suspected cases should be isolated from other patients and strict barrier nursing techniques practised. All hospital personnel should be briefed on the nature of the disease and its routes of transmission. Particular emphasis should be placed on ensuring that high-risk procedures such as the placing of intravenous lines and the handling of blood, secretions, catheters and suction devices are done under barrier nursing conditions. Hospital staff should have individual gowns, gloves and masks. Gloves and masks must not be reused unless disinfected. Patients who die from the disease should be promptly buried or cremated.

Contacts
As the primary mode of person-to-person transmission is contact with contaminated blood, secretion or body fluids, any person who has had close physical contact with patients should be kept under strict surveillance, i.e. body temperature checks twice a day, with immediate hospitalization and strict isolation recommended in case of temperatures above 38.3 C (101 F). Casual contacts should be placed on alert and asked to report any fever. Surveillance of suspected cases should continue for three weeks after the date of their last contact. Hospital personnel who come into close contact with patients or contaminated materials without barrier nursing attire must be considered exposed and put under close supervised surveillance.

History and Prevalence
The Ebola virus was first identified in a western equatorial province of Sudan and in a nearby region of Zaire in 1976 after significant epidemics in Yamkubu, northern Zaire, and Nzara, southern Sudan. Between June and November 1976 the Ebola virus infected 284 people in Sudan, with 117 deaths. In Zaire there were 318 cases and 280 deaths in September and October. An isolated case occurred in Zaire 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, Zaire 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.

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.

Natural Reservoir
The natural reservoir of the Ebola virus is not known. Extensive ecological studies are currently under way in Côte d'Ivoire, Gabon and Zaire to identify the reservoir. Ebola-related filoviruses were isolated from cynomolgus monkeys (Macacca fascicularis) imported into the United States of America from the Philippines in 1989. A number of the monkeys died and at least four persons were infected, although none of them suffered clinical illness.

For more information, please contact the Office of Press and Public Relations, WHO Geneva, Tel: (41 22) 791 2584 or Fax: (41 22) 791 4858. E:mail: inf@who.ch