Twenty years ago Ebola virus first emerged in simultaneous outbreaks in Sudan (ref 1) and Zaire.(ref 2) Two subsequent outbreaks have occurred, (ref 3,4) but transmission among human populations has not been sustained. Despite substantial progress in our understanding of Ebola we have not identified its natural reservoir or the trigger for its re-emergence in new outbreaks in humans.
As the journal went to press, the World Health Organisation had reported 114 cases of Ebola infection and 79 deaths in a new outbreak centred in Kikwit, a rural town of 400000 situated in Bandundu Province, Zaire, 1000 km from the location of the 1976 outbreak in Zaire.(ref 5) A cordon sanitaire has been placed around the town, but some travellers have circumvented it. The few cases reported in nearby towns have so far been among already ill patients transferred from Kikwit to other hospitals. The index case, seen in early April, was a hospital laboratory worker presumed at first to have typhoid; subsequent cases were initially found among a surgical team and others who cared for the laboratory worker, with secondary spread to other health workers and to family members acting as carers. Two thirds of the deaths have been among health workers. Until the outbreak provoked a response, Kikwit General Hospital was short of barrier nursing supplies and disinfectants.
The current outbreak resembles earlier African out breaks, (ref 1,2,3) in which the first cases were found in hospitals where infection control mechanisms were not in place because of economic constraints. Ebola virus was spread to health workers in contact with body fluids, and also from patient to patient by the reuse of unsterilised needles. Secondary transmission occurred also among family members who administered care, among those who prepared corpses for burial, and in other towns where travellers from the epicentre subsequently became ill and infected new carers. Airborne spread is not considered important; one study noted that those exposed to ill patients even in small, crowded village huts were not at increased risk without direct contact.(ref 3)
Illness occurs 2 - 21 days after infection but generally within 7 - 14 days, beginning abruptly with headache, malaise, and fever; vomiting, bloody diarrhoea, or a maculopapular rash may develop a few days later. Severe bleeding and shock may follow and are likely to lead to death. No treatment exists beyond supportive care. Mortality reportedly ranges from 50% to 90%.(ref 1,2,3) Two thirds of cases have resulted in death in the current outbreak, but experience with more extensively studied viral haemorrhagic fevers suggests that very mild cases may go unrecognised. Early cases may also be difficult to differentiate from typhoid or malaria, and not even the late signs are specific; the identification of presumptive cases may be more difficult at present because of an unconfirmed outbreak of shigella dysentery.
Ebola and Marburg are members of a unique ribonucleic acid virus family, the filoviridae.(ref 6) Ebola virus nuclear protein and polymerase genes are distantly related to the equivalent paramyxovirus genes.(ref 7)The reason for the extreme pathogenicity of these agents is not understood. Virulence varies among strains (ref 8); sequencing of the current strain in Zaire by the United States Centers for Disease Control and Prevention shows that it resembles the one that caused the outbreak in 1976.(ref 9)
Past outbreaks have been contained by identifying cases and introducing simple measures to prevent direct contact with body fluids and to limit travel. Experience indicates that nursing supplies, disinfectants, case identification measures, and the isolation and supportive care of ill patients are likely to be best provided where the outbreak is based, once national and international responses are in place. Public health officials must not only effect these measures but convince local people that they minimise risk not only to other communities but to themselves by staying put. Reassuring the public that people who have not been ill cannot transmit Ebola, even if they are infected, is difficult but crucial.
Specific guidance to consultants in communicable disease control, public health doctors, and port medical officers have been issued swiftly here and in similar countries unlikely to be affected by the outbreak. The response has been low key, with no quarantine placed on travellers from Zaire who are not ill and therefore not infectious.(ref 10) Timely communications and a coordinated response from clinicians, public health specialists, and virologists seem to have minimised media overreaction and public concern.
Local, national, and international responses in Zaire, involving a much greater need for resources, have also been put into place. Zaire is fortunate to have its own epidemiologist with experience in the previous outbreak to coordinate these responses. Within days, surveillance systems were operating and early exaggerated reports were contradicted. International teams soon arrived to provide additional epidemiological and clinical support. Bodies are now being picked up and disposed of by the Red Cross, and the community has been educated about the simple measures necessary to minimise risk. Active case finding is taking place at health centres within Kikwit and at remote sites within a radius of 150-200 km; cases and deaths are being systematically identified and contacts exhaustively traced. Gowns, gloves, and masks have been flown in; nurses from peripheral health posts are receiving training. Kikwit's hospital now has access to drinking water and a few hours of electricity daily; surfaces are regularly disinfected.
Despite all this, the number of cases will inevitably rise in the next three weeks among those already infected. The experience so far underlines the importance of disease surveillance for an early response and provokes a commitment to support the intensive efforts until the outbreak is contained. But the outbreak also highlights the difficulties poorer countries have in sustaining the simple measures that could have prevented or minimised not only Ebola transmission but other more ordinary but no less dangerous nosocomial risks.
Deaths from an exotic, incompletely characterised virus should not be necessary to remind us of the need for barrier nursing supplies and routine precautions when there is exposure to body fluids. The present opportunity for rich countries to bring the weight of modern molecular virology to bear on Ebola virus should not deflect from the greater priority to strengthen training of health care staff and improve facilities in poorer countries.
Diane Bennett Consultant epidemiologist Communicable Disease Surveillance Centre Public Health Laboratory Service London NW9 SEQDavid Brown Director Enteric and Respiratory Virus Laboratory Public Health Laboratory Service