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infectious disease occurring in humans and some primates caused by the Ebola virus.
Ebola was first discovered in 1976, and since its discovery, different strands of Ebola have caused epidemics with 50 to 90 percent mortality in the Democratic Republic of the Congo, Gabon, Uganda and Sudan.
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 assiociated 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 5nm. 7nm glycoprotein spikes which are 10nm 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–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).
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.
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.
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, arthralgia, 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, 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.
New Information : Government scientists have developed a new vaccine against the dread Ebola virus that works rapidly after a single injection, an unexpected success that means the nation could soon have a defense against one of the most fearsome weapons in the terrorist arsenal.
So far the vaccine has been proven to work only in monkeys, which were completely protected against death from Ebola infection when they were exposed to the virus a month after being inoculated. But vaccine results in monkeys usually translate well to humans, and government scientists hope to launch human tests of the vaccine by sometime next year. If all goes well, the vaccine could enter government stockpiles in large quantity as a safeguard against Ebola outbreaks, natural or man-made, as soon as 2006, a decade sooner than many scientists once thought it would take to get an Ebola vaccine.
At the same time, the work, to be reported in tomorrow's edition of the journal Nature, raises complex new scientific questions with implications for national security.
The new technique used to create the Ebola vaccine, which involved sophisticated genetic engineering, may be used to create vaccines against other germs, including AIDS and potential terrorist agents. But studies suggest it's possible that any given person could receive a vaccine of this type only once -- subsequent shots might fail to work. That means the government must think carefully about how to use the approach, and about whether to try to maximize its value by, for instance, creating a combination vaccine that would protect against multiple bioterror agents.
Terrifying human outbreaks of Ebola virus have been occurring regularly in Africa, and because the new vaccine works so rapidly, it may well be pressed into service to try to stop one of those epidemics even before the vaccine is formally approved by the Food and Drug Administration.
And eventually, the vaccine could find a highly unusual use in Africa. Ebola is devastating wild populations of gorillas and chimpanzees in parts of the continent, and many scientists have recently realized that the disease, along with a rising illicit trade in ape meat for human consumption, threatens the long-term existence of humankind's closest animal relatives.
Ape biologists universally think a vaccine might be used in captive apes or other special groups to protect them against Ebola, but a few want to go further, vaccinating at least some apes in the wild to try to create barriers to the geographic spread of Ebola virus. The notion raises issues both philosophical and practical issues -- even if it were deemed a good idea, catching thousands of wild gorillas to give them shots would be no mean feat. But if the vaccine continues to hold up in tests, a debate on the issue seems likely.
The virus spreads readily from person to person, then kills 90 percent of the people it infects, dissolving internal tissue and sending blood oozing from nearly every orifice of the victim's body. Only two laboratories in the United States, one of them in Frederick, and only a handful in the world have enough safeguards to permit scientists to work on the Ebola virus. Recurring Ebola epidemics in Africa, most recently in the Congo, have killed scores of people at a time, although the disease provokes such alarm that people do whatever is necessary to limit its spread. Many scientists think the United States has escaped a lethal Ebola outbreak only by luck.
In the 1990s, experts realized that Ebola could make a frightening weapon in the hands of terrorists, and their alarm only deepened when they learned that the Soviet Union, in a vast, illegal biowarfare program, had succeeded in creating weapons using Ebola virus. It's still unclear how many people such a weapon could kill, but no one doubts that even a small-scale attack using Ebola virus would set off mass panic. The anthrax attacks of late 2001 created widespread public anxiety even though anthrax does not spread from person to person, treatment is available and those attacks ultimately killed five people.
Work on an Ebola vaccine goes back years, but only after the 2001 terrorist attacks did serious money start moving into the field. The new vaccine is the product of a successful collaboration between two units of the sometimes-fractious federal health bureaucracy.
The Vaccine Research Center, a unit of Fauci's institute at the National Institutes of Health, in Bethesda, proved three years ago that Ebola vaccination would be possible. But the initial approach was complicated and time-consuming, involving two different types of shots and taking six months or longer to produce immunity. Such a vaccine might be useful to protect health-care workers or soldiers -- it remains under development, in fact -- but it would not be useful to stop an Ebola epidemic.
As NIH worked on a vaccine, the lab in Frederick that works with live Ebola virus, part of the U.S. Army Medical Research Institute of Infectious Diseases, met repeated frustration in its own attempts at vaccine development, creating vaccines that worked in rodents but failed in monkeys, whose biology closely resembles that of humans. At the same time, the Army lab was perfecting an "animal model" the closely resembles human Ebola disease, using macaques, a type of monkey.
The two groups eventually formed a collaboration, and as the scientists were brainstorming, they wondered if one component of the NIH's complicated experimental Ebola vaccine might work as a vaccine all by itself. On a hunch, the scientists decided to test the idea in the macaques.
To everyone's surprise, it worked remarkably well. Some monkeys got a single injection of the test vaccine, and some got a fake injection. A month later, they were deliberately infected with Ebola. Those that got the placebo died the usual horrible death, and the ones that got the vaccine didn't get sick at all.
Human tests of the first vaccine, the one that requires months of shots, could begin by late this year, while tests of the newer approach could begin in 2004, Nabel said.
The new vaccine does pose some new, and complicated, scientific questions. It was created by genetically manipulating a benign virus called adenovirus to make it look, to the immune system, like Ebola. That causes an immune response that works against subsequent Ebola infection, warding off illness. The approach is theoretically attractive for many types of illness, including other terrorist agents, but it may turn out to have significant limitations.
Some unknown proportion of the population already has natural immunity to adenovirus that could be strong enough to prevent the vaccine from working. Scientists are thinking up ways around that problem, but even if they succeed, a given person might be able to receive an adenovirus vaccine only once, because that first shot would create an immune response that might prevent subsequent adenovirus vaccines from working.
Scientists said the situation could prompt a debate within the government about which adenovirus vaccine should receive the highest priority, or whether to try to create a combination adenovirus vaccine to protect against multiple terrorist agents.
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:
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. It is unknown how many people would be willing to do this.
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.
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