Ebola virus

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Ebola virus

(ēbō`lə), a virus of the genus Ebolavirus, which belongs to a family (Filoviridae) of RNA virusesvirus,
parasite with a noncellular structure composed mainly of nucleic acid within a protein coat. Most viruses are too small (100–2,000 Angstrom units) to be seen with the light microscope and thus must be studied by electron microscopes.
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 that cause hemorrhagic fevers. The viruses, named for a river in Congo (Kinshasa) near where the first species was first identified in 1976, emerged from the rain forest, where they survive in as yet unconfirmed hosts, possibly several species of fruit bats (one Ebolavirus species has been found in some fruit bats) but potentially other mammal species; experimental evidence suggests that wild and domestic swine may be a reservoir of the disease. The virus can be fatal to chimpanzees and gorillas as well as humans.

Several species of Ebolavirus found in Africa cause Ebola virus disease (formerly known as Ebola hemorrhagic fever); one found in the W Pacific, which was first identified (1989) in monkeys imported into the United States, does not. Once a person is infected, the disease has an incubation period of 2–21 days; however, some infected persons are asymptomatic. Initial symptoms are sudden malaise, headache, and muscle pain, progressing to high fever, diarrhea, vomiting, symptoms of kidney and liver impairment, and in some cases severe hemorrhaging (internally and out of the eyes and mouth). In 25%–90% of patients, death results, usually within days. The virus is transmitted in body fluids and secretions; it may possibly also be transmitted through the air by aerosol droplets.

A vaccine, rVSV-ZEBOV, has been developed against the species, Zaire ebolavirus, that caused the 2013–15 West African outbreak. It was effective, but it was experimental at the time and saw limited use during that outbreak. Several experimental treatments (an antiviral drug and cloned antibodies) and the vaccine were used in the 2018–19 Congo outbreak, and helped lower fatality rates and protect health-care workers and others in contact with patients. Treatments involved cloned antibodies (REGN-EB3 and mAb114) proved more effective, and were especially effective when begun early. It is unclear if the protection provided by the vaccine will be long lasting. Other vaccines are in development.

Outbreaks of Ebola virus in humans have typically occurred in tropical rainforest regions in Central and West Africa. Among the countries affected have been Congo-Kinshasa (then Zaïre) and Sudan (in a region now in South Sudan), where outbreaks occurred in 1976 and 1979; since then other outbreaks have occurred in Gabon, Uganda, and both Congos. The largest and deadliest outbreak began in late 2013 in Guinea and spread to neighboring Liberia and Sierra Leone, with a few cases in some nearby African nations and in the United States and Europe; some 11,300 people—many more than in any prior outbreak—died in the following two years. Outbreaks have been exacerbated by underequipped and understaffed medical facilities, families caring for patients at home, suspicions that medical personnel are spreading the disease, and other factors.

Bibliography

See D. Quammen, Ebola (2014).

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Ebola virus

Ebola viruses are a group of exotic viral agents that cause a severe hemorrhagic fever disease in humans and other primates. The four known subtypes or species of Ebola viruses are Zaire, Sudan, Reston, and Côte d'Ivoire (Ivory Coast), named for the geographic locations where these viruses were first determined to cause outbreaks of disease. Ebola viruses are very closely related to, but distinct from, Marburg viruses. Collectively, these pathogenic agents make up a family of viruses known as the Filoviridae.

Filoviruses have an unusual morphology, with the virus particle, or virion, appearing as long thin rods. A filovirus virion is composed of a single species of ribonucleic acid (RNA) molecule that is bound together with special viral proteins, and this RNA–protein complex is surrounded by a membrane derived from the outer membrane of infected cells. Infectious virions are formed when the virus buds from the surface of infected cells and is released. Spiked structures on the surface of virions project from the virion and serve to recognize and attach to specific receptor molecules on the surface of susceptible cells, allowing the virion to penetrate the cell. The genetic information contained in the RNA molecule directs production of new virus particles by using the cellular machinery to drive synthesis of new viral proteins and RNA. See Ribonucleic acid (RNA), Virus

Although much is known about the agents of Ebola hemorrhagic fever disease, the ecology of Ebola viruses remains a mystery. The natural hosts of filoviruses remain unknown, and there has been little progress at unraveling the events leading to outbreaks or identifying sources of filoviruses in the wild. Fortunately, the incidence of human disease is relatively rare and has been limited to persons living in equatorial Africa or working with the infectious viruses. The virus is spread primarily through close contact with the body of an infected individual, his or her body fluids, or some other source of infectious material.

Ebola virus hemorrhagic fever disease in humans begins with an incubation period of 4–10 days, which is followed by abrupt onset of illness. Fever, headache, weakness, and other flulike symptoms lead to a rapid deterioration in the condition of the individual. In severe cases, bleeding and the appearance of small red spots or rashes over the body indicate that the disease has affected the integrity of the circulatory system. Individuals with Ebola virus die as a result of a shock syndrome that usually occurs 6–9 days after the onset of symptoms. This shock is due to the inability to control vascular functions and the massive injury to body tissues.

It appears that the immune response is impaired and that a strong cellular immune response is key to surviving infections. This immunosuppression may also be a factor in death, especially if secondary infections by normal bacterial flora ensue. See Immunosuppression

Outbreaks of Ebola virus disease in humans are controlled by the identification and isolation of infected individuals, implementation of barrier nursing techniques, and rapid disinfection of contaminated material. Diagnosis of Ebola virus cases is made by detecting virus proteins or RNA in blood or tissue specimens, or by detecting antibodies to the virus in the blood.

Dilute hypochlorite solutions (bleach), 3% phenolic solutions, or simple detergents (laundry or dish soap) can be used to destroy infectious virions. No known drugs have been shown to be effective in treating Ebola virus (or Marburg virus) infections, and protective vaccines against filoviruses have not been developed.

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.
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