Outbreak of Ebola Viral Hemorrhagic Fever—Zaire, 1995

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Outbreak of Ebola Viral Hemorrhagic Fever—Zaire, 1995

Report excerpt

By: Centers for Disease Control and Prevention (CDC)

Date: May 19, 1995

Source: Centers for Disease Control and Prevention. "Outbreak of Ebola Viral Hemorrhagic Fever—Zaire, 1995." Morbidity and Mortality Weekly Report (2005): May 19;44(19):381-2.

About the Author: The Centers for Disease Control and Prevention is a federal government agency that provides health and safety information for United States citizens and international health professionals. It reports accurate and timely information regarding health issues, and develops and applies disease prevention and control measures. The CDC is also involved in health promotion and education.


An emergent disease can be a disease which appears suddenly and for the first time, or a known and previously controllable disease that again becomes problematic. An example of the latter is tuberculosis. An example of the former is Ebola.

Ebola is a viral disease. The Ebola virus is one of two members of a family designated as the Filoviridae. The name of the virus comes from a river in the Democratic Republic of the Congo, where the first outbreak of the disease occurred.

Ebola produces a high fever, headache, muscle aches, abdominal pain, tiredness, and diarrhea within a few days of infection. Bloody diarrhea and vomiting of blood can also occur. At this stage recovery is possible. But, for most the disease quickly progresses to produce copious internal bleeding, shock, and death. The infection is lethal in over 90 percent of cases. As well, the disease is highly contagious. Thus, an outbreak can quickly devastate a community, often to die out just as quickly, since death can occur before the virus has been transmitted to another host.

As of 2005, four species of Ebola virus have been identified. The speciation is based on immunological differences and variation in genetic sequences. Three of the species—Ebola-Zaire (isolated in 1976), Ebola-Sudan (also isolated in 1976), and Ebola-Ivory Coast (isolated in 1994)—cause disease in humans. The fourth species, Ebola-Reston (named for the United States military primate research facility where the virus was isolated, during a 1989 outbreak of the disease), causes the disease in primates. The Ebola Reston strain (type of the virus) can be transmitted from primates to humans, but does not seem capable of causing disease in humans.

The source of the Ebola virus is still unknown. However, its structural and symptomatic similarities to filovirus, which establish a latent (slow to grow or dormant) infection in African monkeys, macaques, and chimpanzees, make it very conceivable that the Ebola virus likewise normally resides in an African primate. However, as of 2006, this possibility has not been confirmed. Indeed, recent evidence indicates that fruit bats or elephants may also be a reservoir for the virus.

Almost all confirmed human cases of Ebola have occurred in Africa, although two laboratory workers in England and Russia developed Ebola fever as a result of a laboratory accident in which the workers' skin was punctured by a needle contaminated with the virus.

Person-to-person spread of the virus likely requires immediate contact. The possibility of airborne transmission of the virus is debatable. In the Reston outbreak, the primate Ebola strain may have spread via the air distribution system, since some of the monkeys that were infected were never in physical contact with the other infected monkeys. However, this has never been confirmed, nor has a similar method of spread been documented with the pathogenic human strains.

The CDC responded to an outbreak of hemorrhagic fever in Zaire in May 1995 that was found to be Ebola. The CDC team collected blood samples from victims and suspected cases, cared for persons with Ebola, monitored personal contacts of the victims for signs of infection, tracked the cause and origins of the outbreak, and helped with containment measures. The following excerpt is taken from a preliminary report during the investigation.


Outbreak of Ebola Viral Hemorrhagic Fever—Zaire, 1995

On May 6, 1995, CDC was notified by health authorities and the U.S. Embassy in Zaire of an outbreak of viral hemorrhagic fever (VHF)-like illness in Kikwit, Zaire (1995 population: 400,000), a city located 240 miles east of Kinshasa. The World Health Organization and CDC were invited by the Government of Zaire to participate in an investigation of the outbreak. This report summarizes preliminary findings from this ongoing investigation.

On April 4, a hospital laboratory technician in Kikwit had onset of fever and bloody diarrhea. On April 10 and 11, he underwent surgery for a suspected perforated bowel. Beginning April 14, medical personnel employed in the hospital to which he had been admitted in Kikwit developed similar symptoms. One of the ill persons was transferred to a hospital in Mosango (seventy-five miles west of Kikwit). On approximately April 20, persons in Mosango who had provided care for this patient had onset of similar symptoms.

On May 9, blood samples from fourteen acutely ill persons arrived at CDC and were processed in the biosafety level four laboratory; analyses included testing for Ebola antigen and Ebola antibody by enzyme-linked immunosorbent assay, and reverse transcription-polymerase chain reaction (RT-PCR) for viral RNA. Samples from all fourteen persons were positive by at least one of these tests; eleven were positive for Ebola antigen, two were positive for antibodies, and twelve were positive by RT-PCR. Further sequencing of the virus glycoprotein gene revealed that the virus is closely related to the Ebola virus isolated during an outbreak of VHF in Zaire in 1976.

As of May 17, the investigation has identified ninety-three suspected cases of VHF in Zaire, of which eighty-six (ninety-two percent) have been fatal. Public health investigators are now actively seeking cases and contacts in Kikwit and the surrounding area. In addition, active surveillance for possible cases of VHF has been implemented at thirteen clinics in Kikwit and fifteen remote sites within a 150-mile radius of Kikwit. Educational and quarantine measures have been implemented to prevent further spread of disease. Reported by: M Musong, MD, Minister of Health, Kinshasa, T Muyembe, MD, Univ of Kinshasa; Dr. Kibasa, MD, Kikwit General Hospital, Kikwit, Zaire. World Health Organization, Geneva. Div of Viral and Rickettsial Diseases, and Div of Quarantine, National Center for Infectious Diseases; International Health Program Office, CDC.


Editorial Note: Ebola virus and Marburg virus are the two known members of the filovirus family. Ebola viruses were first isolated from humans during concurrent outbreaks of VHF in northern Zaire and southern Sudan in 1976. An earlier outbreak of VHF caused by Marburg virus occurred in Marburg, Germany, in 1967 when laboratory workers were exposed to infected tissue from monkeys imported from Uganda. Two subtypes of Ebola virus—Ebola-Sudan and Ebola-Zaire—previously have been associated with disease in humans. In 1994, a single case of infection from a newly described Ebola virus occurred in a person in Cote d'Ivoire. In 1989, an outbreak among monkeys imported into the United States from the Philippines was caused by another Ebola virus but was not associated with human disease.

Initial clinical manifestations of Ebola hemorrhagic fever include fever, headache, chills, myalgia, and malaise; subsequent manifestations include severe abdominal pain, vomiting, and diarrhea. Maculopapular rash may occur in some patients within five to seven days of onset. Hemorrhagic manifestations with presumptive disseminated intravascular coagulation usually occur in fatal cases. In reported outbreaks, fifty percent to ninety percent of cases have been fatal.

The natural reservoirs for these viruses are not known. Although nonhuman primates were involved in the 1967 Marburg outbreak, the 1989 U.S. outbreak, and the 1994 Cote d'Ivoire case, their role as virus reservoirs is unknown. Transmission of the virus to secondary cases occurs through close personal contact with infectious blood or other body fluids or tissue. In previous outbreaks, secondary cases occurred among persons who provided medical care for patients; secondary cases also occurred among patients exposed to reused needles. Although aerosol spread has not been documented among humans, this mode of transmission has been demonstrated among nonhuman primates. Based on this information, the high fatality rate, and lack of specific treatment or a vaccine, work with this virus in the laboratory setting requires bio-safety level four containment.

CDC has established a hotline for public inquiries about Ebola virus infection and prevention ({800} 900-0681). CDC and the State Department have issued travel advisories for persons considering travel to Zaire. Information about travel advisories to Zaire and for air passengers returning from Zaire can be obtained from the CDC International Travelers' Hotline, (404) 332-4559.


There is no cure for the infection caused by the Ebola virus. However, near the end of an outbreak of the virus in 1995 in Kikwit, Africa, blood products from survivors of the infection were transfused into those actively experiencing the disease. Of those eight people who received the blood products, only one person died. Whether or not the transfused blood conveyed some protective factor could not be determined.

The devastating nature of an Ebola infection is remarkable given the very small size of the viral genome. Fewer than a dozen genes have been detected. How the virus establishes an infection and evades the host immune system armed with so few proteins is still mysterious, and the subject of ongoing study.

Teams of scientists from the Special Pathogens Branch at the CDC continue to investigate outbreaks of emerging diseases including Ebola, along with teams from the World Health Organiztion. In the latest Ebola outbreak that occurred in April 2005 in a forested area of the Cuvette-Ouest region that borders Gabon, more than twenty people died before the outbreak dissipated.

Ebola and other emergent diseases are also significant because they may be indicative of a shifting natural ecological balance. In the case of Ebola, the increasing encroachment of humans into previously pristine territory may have brought our species into contact with hitherto un-encountered microbes. Alternately, agricultural practices such as the use of poultry "factory farms", housing millions of birds, may have created conditions conducive to the rapid spread of avian influenza. The avian influenza has so far established disease in few humans. Yet, the highly mutable genome of the virus (which is similar in sequence to that of the influenza virus that caused the devastating epidemic of 1918) makes adaptation of the virus to a human host a foreseeable possibility.



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