A virus, first isolated in 1976 in Africa, belonging to the Filoviridae family, which causes severe and often fatal haemorrhagic fevers in humans and non-human primates. It is classified as a biosafety level 4 agent because of its extreme pathogenicity and the lack of a protective vaccine or anti-viral drug. Little is known of its natural history and its host is still unidentified. In June 2005 it was reported that a vaccine that protects monkeys from the Ebola and Marburg viruses had been developed. Research is continuing into a vaccine to protect humans.
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Classifications and external resources
| ICD-10 | A98.4 | |
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| ICD-9 | 065.8 | |
| DiseasesDB | 18043 | |
| MedlinePlus | 001339 000000 | |
| eMedicine | med/626 | |
| MeSH | C02.782.417.415 | |
Ebola is the common term for a group of viruses belonging to genus Ebolavirus, family Filoviridae, which cause Ebola hemorrhagic fever.
The virus is named after the Ebola River in the African nation-state of the Democratic Republic of the Congo (formerly Zaïre), near the site of the first outbreaks.The Democratic Republic of Congo has been the site of four recent outbreaks, including one in May 2005. Ebola is believed to be a zoonotic virus, although despite considerable effort by the World Health Organization, no animal reservoir capable of sustaining the virus between outbreaks has been identified. Because Ebola is lethal and since no approved vaccine or treatment is available, Ebola is classified as a Biosafety Level 4 agent;
The symptoms of Ebola are rather similar to that of the Marburg virus, which is also in the family Filoviridae.
Structure
Size and shape
Electron micrographs of members of Ebolavirus show them to have the characteristic thread-like structure of a filovirus. On average however, the length of a typical Ebola virus is closer to 1000 nm.
Genome
Each virion contains one molecule of linear, single-stranded, negative-sense RNA, totalling 18900 nucleotides in length.
Species
Zaïre Ebolavirus
The Zaïre Ebolavirus has the highest mortality rate, up to 90% in some epidemics, with an average of approximately 83% mortality over 27 years.
The first outbreak took place on August 26, 1976 in Yambuku, a town in the north of Zaïre.
Soon after, more patients arrived with varying but similar symptoms including fever, headache, muscle and joint aches, fatigue, nausea and dizziness.
Sudan Ebolavirus
The most recent outbreak of Sudan Ebolavirus occurred in May 2004.
Reston Ebolavirus
First discovered in November of 1989 in a group of 100 Crab-eating monkeys (Macaca fascicularis) imported from the Philippines to Reston, Virginia.
Further Reston Ebolavirus infected monkeys were shipped again to Reston, and Alice, Texas in February of 1990.
Ivory Coast Ebolavirus
This species of Ebola was first discovered amongst chimpanzees of the Tai Forest in Côte d’Ivoire, Africa. Studies of tissues taken from the chimps showed results similar to human cases during the 1976 Ebola outbreaks in Zaïre and Sudan.
One of the scientists performing the necropsies on the infected chimpanzees contracted Ebola.
Replication
The viral attachment protein recognizes specific receptors, which may be protein, carbohydrate or lipid, on the outside of the cell.
The virus next activates and releases its own genetic material, causing the host to begin manufacturing the proteins necessary for virus reproduction using its own resources. The spread of the virus through the population can be halted if the proper sterilization and quarantine measures are taken, as the only method by which the virus may continue to propagate is via direct contact with body fluids.
Ebola hemorrhagic fever
Symptoms
Symptoms are varied and often appear suddenly.
Ebola goes on to cause diarrhea, dark or bloody stool, vomiting blood, red eyes from swollen blood vessels, red spots on the skin from subcutaneous bleeding, maculopapular rash, purpura, and bleeding internally and externally from any orifice, including from the nose, mouth, rectum, genitals or needle puncture sites.
Other secondary symptoms include hypotension (less than 90mm Hg), hypovolemia, tachycardia, severe organ damage (especially the kidneys, spleen, and liver) as a result of disseminated systemic necrosis, and proteinuria.
Transmission
Among humans, the virus is transmitted by direct contact with infected body fluids, or to a lesser extent, skin or mucus membrane contact.
Although airborne transmission between monkeys has been demonstrated in a laboratory, there is very limited evidence for human-to-human airborne transmission in any reported epidemics.
So far all epidemics of Ebola have occurred in sub-optimal hospital conditions, where practices of basic hygiene and sanitation are often either luxuries or unknown to caretakers and where disposable needles and autoclaves are unavailable or too expensive. In modern hospitals with disposable needles and knowledge of basic hygiene and barrier nursing techniques, Ebola rarely spreads on such a large scale.
In the early stages, Ebola may not be highly contagious.
Treatments
Treatment is primarily supportive and includes minimizing invasive procedures, balancing electrolytes, replacing lost coagulation factors to help stop bleeding, maintaining oxygen and blood levels, and treating any complicating infections. Despite some initial anecdotal evidence, blood serum from Ebola survivors has been shown to be ineffective in treating the virus. In early 2006, scientists at USAMRIID announced a 75% recovery rate after infecting four rhesus monkeys with Ebola virus and administering antisense drugs.
Vaccines
Vaccines have been produced for both Ebola and Marburg that were 100% effective in protecting a group of monkeys from the disease. These vaccines are based on either a recombinant Vesicular stomatitis virus or a recombinant Adenovirus carrying the Ebola spikeprotein on its surface.
Ebola as a Weapon
Ebola is classified as a Category A Biological terrorism agent by the CDC as well as being considered a select agent that has the "potential to pose a severe threat to public health and safety".
Ebola shows potential as a biological weapon because of its lethality but due to its short incubation period it may be more difficult to spread since it may kill its victim before it has a chance to be transmitted. The Soviet biological weaponry program reportedly succeeded in mixing Ebola with smallpox and the Venezuelan equine encephalitis virus.
As a terrorist weapon, Ebola has been considered by members of Japan's Aum Shinrikyo cult, whose leader, Shoko Asahara led about 40 members to Zaire in 1992 under the guise of offering medical aid to Ebola victims in what was presumably an attempt to acquire a sample of the virus.
Cultural impact
Ebola and marburg has served as a rich source of ideas and plotlines for many forms of entertainment.
Much of the representation of the Ebola virus in fiction and the media is considered exaggerated or myth. Many of the stories about Ebola in Preston's book The Hot Zone are refuted in the book Level 4: Virus Hunters of the CDC by Joseph B.
Another myth states that the symptoms of the virus are horrifying beyond belief. Victims of Ebola suffer from squirting blood, liquifying flesh, zombie-like faces and dramatic projectile bloody vomiting. In actual fact, only a fraction of Ebola victims have severe bleeding that would be even somewhat dramatic to witness. Ebola symptoms are usually limited to extreme exhaustion, vomiting, diarrhea, abdominal pain, a high fever, headaches and other body pains.
The following is an excerpt from an interview with Philippe Calain, M.D.
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