What is the ebola virus?

Causes and Symptoms

The Ebola virus is named after the Ebola River in northern Zaire (now the Democratic Republic of the Congo), Africa. The virus was first detected in 1976, when hundreds of deaths were recorded in Zaire as well as in neighboring Sudan. Four species of the Ebolavirus genus cause human disease: Zaire ebolavirus (EBOV), Sudan ebolavirus (SUDV), Bundibugyo ebolavirus (BDBV), and Taï Forest ebolavirus (TAFV). A fatal disease among cynomolgus laboratory monkeys that were imported from the Philippines to Texas in 1996 was caused by the Reston ebolavirus (RESTV) subtype, which causes disease in nonhuman primates and in pigs but is not known to cause symptoms in humans. Another devastating outbreak among humans took place in early 1995 in Kikwit, Zaire, claiming the lives of 250 out of 315 reported patients, an 88 percent fatality rate. The epidemic ended within a few months, as suddenly as it began; this puzzled scientists, who are still not fully aware of the causes and nature of the virus. Despite the dreadful speed with which the disease killed its victims, scientists were able to contain it with a relatively small number of fatalities.

Outbreaks in Africa have continued to occur, some of them severe. A 2007 outbreak in the Democratic Republic of the Congo resulted in 264 cases and 187 deaths. Starting in February 2014, several West African countries were hit by the largest outbreak to date, with 3,069 reported cases (both confirmed and suspected) and 1,552 deaths as of August 26. Between September and October 2014, one man who had traveled to the United States from Liberia tested positive for Ebola and passed away days later; a handful of health care workers, including two who had been treating the Ebola patient at the hospital in Texas and two who had been missionary workers in Liberia, tested positive for the disease but recovered in the United States. By early March 2015, the Centers for Disease Control, in conjunction with the World Health Organization (WHO), reported 14,314 laboratory-confirmed cases and 9,714 deaths in Guinea, Liberia, and Sierra Leone.

The Ebola virus appears to have an incubation period of two to twenty-one days, after which time the impact is devastating. The patient exhibits appetite loss, increasing fever, headaches, and muscle aches. The next stage involves disseminated intravascular coagulation (DIC), a condition characterized by both blood clots and hemorrhaging. The clots usually form in vital internal organs such as the liver, spleen, and brain, with subsequent collapse of the neighboring capillaries. Other symptoms include vomiting, diarrhea with blood and mucus, and conjunctivitis. An unusual type of skin irritation known as maculopapular rash first appears in the trunk and quickly covers the rest of the body. The final stages of the disease involve a spontaneous hemorrhaging from all body outlets, coupled with shock and kidney failure, and typically death within eight to seventeen days.

Treatment and Therapy

The Ebola virus is classified as a ribonucleic acid (RNA) virus and is closely related to the Marburg virus, first discovered in 1967. Ebolavirus and Marburgvirus are two of only three identified genera in the Filoviridae family, which was first officially established in 1987; the third, Cuevavirus, was only added in 2013.

Electron microscope studies show the Ebola virus as long filaments, 650 to 14,000 nanometers in length, that are often either branched or intertwined. Its virus part, known as the virion, contains one single noninfectious minus-strand RNA molecule and an endogenous RNA polymerase. The lipoprotein envelope contains a single glycoprotein, which behaves as the type-specific antigen. Spikes are approximately seven nanometers in length, are spaced at approximately ten-nanometer intervals, and are visible on the virion surface. It is believed that once in the body, the virus produces proteins that suppress the organism’s immune system, thus allowing its uninhibited reproduction.

In 2002, researchers announced a new discovery about how Ebola enters and subverts human cells. Findings show that the virus targets “lipid rafts,” tiny fat platforms that float atop the membranes of human cells. These rafts act as gateways for the virus, the assembly platform for making new virus particles, and the exit point where new particles bud. This research is a significant step toward one day creating drugs that will stop viruses from replicating.

The Ebola virus can be transmitted through contact with body fluids, such as blood, semen, mucus, saliva, urine, and feces. It is thought that the first person in an outbreak acquires the virus through contact with an infected animal, including carcasses of dead animals. In early 2015, researchers for the National Institutes of Health conducting a study on macaque monkeys determined that the virus can remain infectious in a corpse for up to one week, and it can still be detected for close to ten weeks.

The level of infectivity of the Ebola virus is quite stable at room temperature. Its inactivation is accomplished via ultraviolet or gamma irradiation, 1 percent formalin, beta propiolactone, and an exposure to phenolic disinfectants and lipid solvents, such as deoxycholase and ether. The virus isolation is usually achieved from acute-phase serum of appropriate cell cultures, such as MA-104 cells from the kidney cell line of fetal rhesus monkeys. Satisfactory results have been accomplished using tissues obtained from the liver, spleen, lymph nodes, kidneys, and heart during autopsy. Virus isolation from brain and other nervous tissues, however, has been rather unsuccessful so far. Neutralization tests have been inconsistent for all filoviruses; Ebola strains show cross-reactions in tests of immunofluorescence assays.

There appears to be no known or standard treatment for Ebola fever. No chemotherapeutic or immunization strategies are available, and no antiviral drug has been shown to provide positive results, even under laboratory conditions. There is indirect evidence that convalescent blood transfusions may improve survival rates among patients, and certain monoclonal antibodies and RNA interference (RNAi) therapies have shown some effectiveness in nonhuman primates. During the 2014 outbreak, the monoclonal antibody ZMapp was given to several infected patients with mixed but potentially promising results. As of early 2015, two potential vaccines were under study.

Aside from experimental treatments, therapy for Ebola patients involves sustaining the desired fluid and electrolyte balance by the frequent administration of fluids. Bleeding may be fought off with blood and plasma transfusion. Sanitary conditions to avoid further contact with the disease are required. Proper decontamination of medical equipment, isolation of the patients from the rest of the community, and prompt disposal of infected tissues, blood, and even corpses limit the spread of the disease.

Perspective and Prospects

The puzzling characteristics of the Ebola virus are the location of its primary natural reservoir, its sudden eruption and quick end, and the unusual discovery of the virus in the organs of people who have survived it.

In the past, experimental work on the virus has been slow because of its high pathogenicity. The progress of recombinant deoxyribonucleic acid (DNA) technology has shed the first light on the molecular structure of this virus. It is hoped that further work using this technique as well as results from viruses of lower pathogenicity, such as the Reston virus, will provide the desired information on replication and virus-host interactions. Finally, the improvement of the various diagnostic tools will allow more accurate virus identification and assessment of transmission modes.

In 1995, investigators and epidemiologists from the WHO captured about three thousand birds, rodents, and other animals and insects that were suspected of spreading the disease in order to investigate the source of the virus. The results were obscure and inconclusive, and the main facts about the disease are still a mystery, with the exception of the established link between primates and Ebola virus infection in humans. This conclusion was reached after a researcher in Côte d'Ivoire contracted the Taï Forest virus in 1994 after performing an autopsy on an infected chimpanzee. This was the first—and, as of 2014, only—known human case of the Taï Forest subtype, which was subsequently named for the Taï National Park forest reserve in Côte d'Ivoire where the researcher had been working. The infection ultimately proved nonfatal.

Despite this evidence, however, the human outbreaks in the Democratic Republic of the Congo, Sudan, and West Africa have not been traced to primates. Certain species of fruit bat are suspected to be a natural source of the disease, but evidence of the virus has yet to be isolated in any specimen. As long as these puzzling questions linger, the disease should be contained as much as possible, with particular emphasis on the improvement of sanitary conditions and the control of body-fluid contact.

Bibliography

Balter, Michael. “On the Trail of Ebola and Marburg Viruses.” Science 290.5493 (2000): 923–25. Print.

Biddle, Wayne. A Field Guide to Germs. 3rd ed. New York: Anchor, 2010. Print.

Dyer, Nicole. “Killers without Cures.” Science World 2 Oct. 2000: 8–12. Print.

"Ebola." MedlinePlus. Natl. Lib. of Medicine, 27 Feb. 2015. Web. 3 Mar. 2015.

"Ebola Hemorrhagic Fever." Centers for Disease Control and Prevention. Centers for Disease Control and Prevention, 2 Mar. 2015. Web. 3 Mar. 2015.

"Ebola Virus Disease." World Health Organization. WHO, Sept. 2014. Web. 3 Mar. 2015.

Feldmann, Heinz. "Ebola: A Growing Threat?" New England Journal of Medicine. Massachusetts Medical Soc., 7 May 2014. Web. 28 Aug. 2014.

Gatherer, Derek. "The 2014 Ebola Virus Disease Outbreak in West Africa." Journal of General Virology 95.8 (2014): 1619–24. Print.

Jaax, Nancy, and Jerry Jaax. "Lethal Viruses, Ebola, and the Hot Zone: Worldwide Transmission of Fatal Viruses." E. N. Thompson Forum on World Issues. University of Nebraska–Lincoln. 22 Oct. 1996. Lecture.

Peters, C. J., and J. W. LeDuc. “An Introduction to Ebola: The Virus and the Disease.” Supp. to Journal of Infectious Diseases 179.1 (1999): ix–xvi. Print.

Rollin, Pierre E., et al. “Arenaviruses and Filoviruses.” Manual of Clinical Microbiology. Ed. James Versalovic et al. 10th ed. Vol. 2. Washington: ASM, 2011. 1514–29. Print.

Sifferlin, Alexandra. "Ebola Bodies Are Infectious a Week after Death, Study Shows." Time. Time, 13 Feb. 2015. Web. 3 Mar. 2015.

Strauss, James H., and Ellen G. Strauss. Viruses and Human Disease. 2nd ed. Burlington: Academic, 2008. Print.

"2014 Ebola Outbreak in West Africa." Centers for Disease Control and Prevention. Centers for Disease Control and Prevention, 2 Mar. 2015. Web. 3 Mar. 2015.