|Ebola virus |
An electron micrograph showing
the filamentous structure of the
viral particle. The filaments are
60-80 nm in diameter.
|Scientific classification |
Ivory Coast ebolavirus
Ebola hæmorrhagic fever (EHF — alternatively Ebola hemorrhagic fever; commonly referred to as simply Ebola) is a recently identified, severe, often fatal infectious disease occurring in humans and some primates caused by the Ebola virus.
Ebola was first discovered in 1976, and since its discovery, different strains of Ebola have caused epidemics with 50 to 90 percent mortality in the Democratic Republic of the Congo, Gabon, Uganda and Sudan.
The Ebola virus
The virus comes from the Filoviridae family, of which the Marburg virus is also a member. It is named after the Ebola River in Zaire, Africa, near where the first outbreak was noted by Dr. Ngoy Mushola in 1976 after a significant outbreak in Yambuku, Zaire (now the Democratic Republic of the Congo), and Nzara, in western Sudan. Of 602 identified cases, there were 397 deaths.
The two strains identified in 1976 were named Ebola–Zaïre (EBO–Z) and Ebola–Sudan (EBO–S). The outbreak in Sudan showed a lower fatality rate — 50% — compared to the 90% mortality rate of the Zaïre strain. In 1990, a second, similar virus was identified in Reston, Virginia among monkeys imported from the Philippines, and was named Ebola–Reston. This strain seemed to be spread through the air, but did not cause any human fatalities; although four men did test positive for the virus, none became ill.
Further outbreaks have occurred in Zaire/Democratic Republic of the Congo (1995 and 2003), Gabon (1994, 1995 and 1996), Uganda (2000), and Sudan again (2004). A new subtype was identified from a single human case in the Côte d'Ivoire in 1994, EBO–CI.
Of around 1500 identified Ebola cases worldwide, two-thirds of the patients have died. The animal (or other) reservoir which sustains the virus between outbreaks has not been identified.
Electron micrographs of the Ebola virus show it to have the characteristic filamentous structure of a filovirus. The viral filaments can appear in images in various shapes including a 'u', '6', a coil, or may be branched. The filaments are reported to be between 60-80 nm in diameter; the length of a filament associated with an individual viral particle is extremely variable, with Ebola particles of up to 14,000 nm in length being reported. An average length, which may represent the most infectious particles, is in the region of 1000 nm. The first electronmicrograph of Ebola was obtained on the 13 October 1976 by Dr. F.A. Murphy, now at UC Davis, who was then working at the CDC. The nucleocapsid structure consists of a central channel, 20-30 nm in diameter, surrounded by helically wound capsid with a diameter of 40-50 nm and an interval of 5 nm. 7 nm glycoprotein spikes that are 10 nm apart from each other are present within the outer envelope of the virus, which is derived from the host cell membrane. Each viral particle contains one molecule of single-stranded, negative-sense RNA, which encodes the seven viral proteins.
Ebola virus history
Ebola–Zaïre, the first-discovered Ebola virus, is also the most deadly. At its worst, it has a ninety percent fatality rate. There have been more outbreaks of Ebola–Zaïre than any other strain of Ebola virus. The first outbreak took place in 1976 in Yambuku, Zaire (now the Democratic Republic of the Congo). Mabelo Lokela checked into the local hospital with a fever. One of the nurses assumed Lokela had malaria and gave him a quinine shot. When Lokela returned home from the hospital and died, the women of his family conducted a traditional African funeral for him. In preparation for this funeral, they removed all the blood and excreta from his body with their bare hands. Most of the women in his family died soon afterwards (Draper 19).
Meanwhile, the nurses at the hospital had an Ebola epidemic on their hands. The needle used for Lokela's quinine injection was inadequately sterilized, so Ebola had spread from patient to patient as the needles were reused. They called Dr. Ngoi Mushola, the area director, for help. He taught them how to sterilize their needles and purify water. He also told the nurses to instruct patients' families not to bury their dead inside or close to their homes as tradition dictated, since Ebola could spread from dead bodies. He also called authorities in Kinshasa, the nation's capital, for help. Kinshasa sent a microbiologist and an epidemiologist who performed autopsies on dead patients and collected samples. Soon afterwards, the entire area was quarantined, which soon brought the disease back under control. This quarantine simply meant that the area was isolated until every ill person died. Dr. Ngwete Kikhela, the Minister of Health in Kinshasa, then contacted the United States Centers for Disease Control (CDC) for help. The CDC informed the international medical community about the epidemic (Draper 15-23).
The fatality rate for the 1976 outbreak was 88.05%; the 1977 outbreak 100%; the 1994 outbreak 59.18%; the 1995 outbreak 81.27%; the 1996 outbreak 73.12%; the 2001-2002 outbreak 79.51%; and the 2003 outbreak 90.14%. The total fatality rate for Ebola–Zaïre is 82.60%.
A graphical representation of known human cases and deaths during outbreaks of Ebola
Zaire between 1976
Meanwhile, another outbreak was occurring in the cities of Nzara and Maridi, Sudan. The first case that occurred in Nzara involved a worker who had been exposed to the potential natural reservoir at the local cotton factory. A natural reservoir is a carrier of the virus that is immune to its effects. Although many of the creatures — ranging from spiders to insects to rats and bats — found in the factory were tested for Ebola, none of the tests came back testing positive (Draper 30-31). The natural reservoir for Ebola is still unknown today (Fact Sheet No. 103).
Another case was the death of a nightclub owner in Nzara who could afford to go to the fancier hospital located in Maridi. Unfortunately, the nurses there also did not properly sterilize their needles, and the hospital, like the one in Yambuku, became a breeding ground for new Ebola cases (Draper 30-31). Several epidemics of Ebola-Zaïre and Ebola-Sudan have occurred since 1976.
The most recent outbreak of Ebola–Sudan occurred in May 2004. As of May 24, 2004, 20 cases (including five deaths) of Ebola–Sudan were reported in Yambio County, Sudan. The Centers for Disease Control and Prevention confirmed the virus a few days later. The neighboring countries of Uganda and the Democratic Republic of Congo have increased surveillance in bordering areas, and other similar measures have been taken to control the outbreak.
The fatality rate for the 1976 outbreak was 52.98%; for the 1979 outbreak 67.65%; and for the 2000-2001 outbreak 53.18%. The total fatality rate for Ebola-Sudan is 53.76%
A graphical representation of known human cases and deaths during outbreaks of Ebola
Sudan between 1976
In 1989, crab-eating macaques from the Philippines brought Ebola-Reston into quarantine facilities in Reston, Virginia, Texas, and Pennsylvania. Four people developed antibodies from exposure to the virus, but none fell ill. Ebola–Reston has re-emerged in monkeys several times since then, but no humans have contracted the virus (“Ebola Hemorrhagic Fever Table”). It is unknown why the monkeys became ill, but not the humans (Draper 40).
In 1994, a scientist became ill after conducting an autopsy on a wild chimpanzee. The scientist recovered (“Ebola Hemorrhagic Fever Table”). Not much is known about this form of Ebola since only one case of it has been discovered.
Ebola hemorrhagic fever
Among humans, the virus is transmitted by direct contact with infected body fluids such as blood. The cause of the index case is unknown.
The incubation period of Ebola haemorrhagic fever varies from two days to four weeks. Symptoms are variable too, but the onset is usually sudden and characterised by high fever, prostration, myalgia (muscle pains), arthralgia (pain in the joints), abdominal pains and headache. These symptoms progress to vomiting, diarrhea, oropharyngeal lesions, conjunctivitis, organ damage (notably the kidney and liver) by co-localized necrosis, proteinuria (the presence of proteins in urine), and bleeding both internal and external, commonly through the gastrointestinal tract. Death or recovery to convalescence occurs within six to ten days.
No specific treatment has been proven effective, and no vaccine currently exists. A vaccine is in the developmental stages. Ebola is known to exist in humans and a few monkey species can be infected. To develop the vaccine, monkeys are used but it can not be tested on humans except in outbreak environments so the vaccine must be tested extensively and meet strict government regulations. Also, in the development of a vaccine, accessibility and cost for people of poor nations and the transportation efficiency of it must be considered.
Although there is no specific treatment for patients with Ebola, there have been entire books written about how to prevent it from spreading from the patient to health care workers or other patients. The first step in prevention is to make advanced preparations for Ebola and other viral hæmorrhagic fevers (VHFs). Selecting a VHF Coordinator to oversee preparations for VHF activities, such as the following, does this:
- Serving as the focal point for information and leadership when a VHF case is suspected.
- Informing all health facility staff about VHFs and the risks associated with them.
- Organizing training in VHF Isolation Precautions for staff that will work with VHF patients or infectious body fluids.
- Making sure that teams are trained to prepare and transport bodies for burial (CDC 115-116).
The next step is maintaining a minimum standard of cleanliness in the hospital. This includes washing hands and sterilizing needles (CDC 9-18). Also, the medical staff must be informed about the different types of VHFs, including Ebola, and their symptoms. Symptoms that are common to many VHFs are severe weakness and fatigue, and a fever for more than 72 hours and less than three weeks. The patient also may have unexplained bleeding from the mucous membranes, skin, eyes, or gastrointestinal tract. The patient may also be going into shock (has a blood pressure of less than 90 mm Hg or a rapid weak pulse). Finally, that patient may have had contact with someone in the last three weeks that had an unexplained illness with fever or bleeding or who died with an unexplained severe illness with a fever (CDC 23).
Next, the infected patient must be isolated from other, uninfected patients and from health care workers who are not directly involved in care of the infected patient. The patient should be given intravenous support, as he or she is probably dehydrated from losing fluids through vomiting and diarrhea. Finally, if the patient expires, the body should be properly disposed of, preferably through cremation, so that the dead body will not spread disease to other people (CDC 26).
Ebola has sharply affected tourism in the countries where it is present, especially in the Democratic Republic of the Congo (“TED Case Study”). Other countries that have been hard hit include Uganda, where an outbreak in 2000 stifled its waning tourism industry (Busharizi). Ebola has also made countries like Uganda, Democratic Republic of the Congo, and Sudan to lose revenue through the loss of people who would have been able to work and benefit their nation's economy. For example, many health workers' lives have been lost because they became sick in hospitals due to inadequate sanitation procedures. It is unknown how much money exactly was lost through these deaths (Busharizi).
Another loss in economic revenue has been the deaths of monkeys traded throughout the world for experimental purposes. Three out of the four Japanese airlines that transport monkeys throughout the world have quit transporting monkeys because of the risk of Ebola. Not so long ago, a monkey cost $1500 (USD) to transport, but now costs three times as much, partly because of the monkey ban (“TED Case Study”).
Since Ebola is so unpredictable, it is impossible to detect very many trends that it causes. Ebola first appeared out of nowhere in 1976 and disappeared until 1989 (Draper 6). It is possible to say that since this disease can be transmitted from monkeys to humans, that Ebola will probably reappear in places where there are significant monkey populations in Asia and Africa.
It is not known at this time whether there are individual trends in the Ebola virus, either. As of this date, there is no information about a person who has caught Ebola twice and lived to tell about it, so it is impossible to say whether a person is immune to it after they survive a first episode.
Bioterrorism, or use of the Ebola virus as a biological weapon, is a common fear of people who know about the virus. There is not much information published about the bioterrorism potential of Ebola, obviously for security reasons. However, scientists do say that altering the Ebola virus for biological warfare is possible although unlikely. The difficulty in changing Ebola to a potential virus is twofold: first, the Ebola virus would have to be airborne to be effective. Although some have noted that Ebola can travel through water droplets in the air (Preston 260), it is currently not possible for Ebola to travel through the air by itself (Russell). Second, the Ebola virus would have to be transported in a way that is not fatal to the people who use it as a weapon, or would have to be carried by people who are willing to die a gruesome death.
In his book Biohazard, former Soviet biological warfare researcher Ken Alibek claimed that the former Soviet Union experimented extensively with use of Ebola as a biological weapon.
The book Executive Orders by Tom Clancy describes an extensive bioterrorist attack on the United States via a newly discovered strain of Ebola that propagates by air.
- Breakthrough in Ebola Vaccine (http://news.bbc.co.uk/go/pr/fr/-/2/hi/health/3126365.stm). BBC News World Edition 6 August 2003. 3 September 2003.
- Busharizi, Paul. Ebola Hits Uganda’s Tourism Revival Effort (http://www.planetark.org/dailynewsstory.cfm?newsid=0385). Planet Ark. 27 December 2000. 3 September 2003.
- Centers for Disease Control and Prevention and World Health Organization. Infection for Health Control of Viral Hemorrhagic Fevers in the African Health Care Setting (http://www.cdc.gov/ncidod/dvrd/spb/mnpages/vhfmanual/entire.pdf). Atlanta, Center for Disease Control and Prevention, 1998. 3 September 2003.
- Draper, Allison Stark. Ebola. New York: The Rosen Publishing Group, Inc., 2002.
- Ebola Hemorrhagic Fever (http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/ebola.htm). Centers for Disease Control Special Pathogens Branch. 8 September 2003.
- Ebola Hemorrhagic Fever Table Showing Known Cases and Outbreaks, in Chronological Order (http://cdc.gov/ncidod/dvrd/spb/mnpages/dispages/ebotabl.htm). Centers for Disease Control and Prevention. 18 October 2002. 3 September 2003.
- Fact Sheet Number 103 Ebola Hemorrhagic Fever (http://www.who.int/inf-fs/en/fact103.html). World Health Organization. December 2000. 3 September 2003.
- Filoviruses (http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/filoviruses.htm). Centers for Disease Control Special Pathogens Branch. 3 September 2003.
- Horowitz, Leonard G. Emerging Viruses: AIDS & Ebola — Nature, Accident, or Intentional?. Rockport, MA: Tetrahedron, Inc., 1996.
- Preston, Richard. The Hot Zone. New York: Anchor Books Doubleday, 1994.
- Russell, Brett. What are the Chances? (http://www.brettrussell.com/personal/what_are_the_chances_.html) Ebola FAQ. 3 September 2003.
- TED Case Study: Ebola and Trade (http://www.american.edu/projects/mandala/TED/ebola.htm). Trade and Environment Databases. May 1997. 7 November 2003.