Ebola overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Guillermo Rodriguez Nava, M.D. [2] Alejandro Lemor, M.D. [3]
Overview
Ebola is the common term for a group of viruses belonging to genus Ebola, family Filoviridae, and for the disease which they cause, Ebola hemorrhagic fever. The viruses are characterised by a long, filamentous morphology surrounded by a protein/lipid viral envelope. Ebola viruses are morphologically similar to the Marburg virus, also in the family Filoviridae, and share similar disease symptoms. Ebola has caused a number of serious and highly publicized outbreaks since its discovery.[1]
Historical Perspective
The Ebola virus was named after the Ebola River Valley in the Democratic Republic of the Congo (formerly Zaïre), near the site of a 1976 outbreak at a mission run by Flemish nuns.[2] Since the initial discovery of the virus, five subtypes have subsequently been identified.
Classification
Ebola virus can be classified into 5 subtypes: Zaïre, Sudan, Reston, Tai (Ivory Coast) and Bundibugyo.
Pathophysiology
The Ebola virus infects the mononuclear phagocyte system, but also other cells such as hepatocytes, spongiocytes, fibroblasts and endothelial cells, inducing tissue necrosis and disrupting the hematological and coagulation systems. The Ebola virus is transmitted by direct contact with infected patients or animals. The natural reservoir has not been identified.[3][4][5][6]
Causes
Ebola hemorrhagic fever (Ebola fever) is caused by a virus belonging to the family called Filoviridae. Three types of virus have been reported to cause disease in humans: Ebola-Zaire virus, Ebola-Sudan virus, and Ebola-Ivory Coast virus. The human disease has so far been limited to parts of Africa. A very small number of people in the United States who were infected with the fourth type of the virus, known as Ebola Reston, did not develop any signs of disease.
Differentiating Ebola from other Diseases
There are other conditions, such as Marburg virus, Lassa fever, Typhoid fever and Malaria that involve hemorrhage and/or high fever as part of their presentation, and therefore resemble Ebola virus disease. The clinician must treat the most likely cause of the fever according to local epidemiology and the appropriate treatment guidelines. If the fever continues after 3 days of recommended treatment, and if the patient has signs such as bleeding or shock, the clinician must consider a viral hemorrhagic fever (VHF). It is important to review the patient’s history for any contact with someone who was ill with fever and bleeding or who died from an unexplained illness with fever and bleeding. If no other cause is found for the patient’s signs and symptoms, the clinician must suspect a VHF.[7]
Epidemiology and Demographics
Outbreaks of EVD have mainly been restricted to Africa. The virus often consumes the population. Governments and individuals quickly respond to quarantine the area while the lack of roads and transportation helps to contain the outbreak. The potential for widespread EVD epidemics is considered low due to the high case-fatality rate, the rapidity of demise of patients, and the often remote areas where infections occur.
Risk Factors
The main risk factors for Ebola virus disease are traveling to endemic areas, to be a health professional taking care of infected patients and researchers working with animal models of the Ebola virus disease.[7]
Natural History
Ebola virus disease without supportive care, progresses to eventually cause death. Ebola virus disease can be complicated by the development of multiorgan failure and shock. The prognosis of Ebola virus disease is poor, and depends of the supportive care given and the Ebola virus strain. The Zaire Ebola virus has mortality rate as high as 90%.[7]
Diagnosis
History and Symptoms
Despite the existence of different species of Ebola virus, a common clinical syndrome has been described among these different filoviroses, with the difference residing essentially in the severity of the presentation and respective mortality rate. Ebola hemorrhagic fever is potentially lethal and encompasses a range of symptoms including fever, chills vomiting, diarrhea, generalized pain or malaise, and sometimes internal and external bleeding, that follow an incubation period of 2-21 days.
Physical Examination
Ebola hemorrhagic fever usually begins with an acute onset of high fever, chills and hemorrhage observed on physical examination. Other pertinent findings may include swollen joints, weakness, rash and red eyes. Also, the high fever present in this condition may lead to the development of relative bradycardia, similarly to typhoid fever. [8][9][10]
Laboratory Findings
There are no specific laboratory findings of Ebola virus disease. Some nonspecific findings include alterations in the white blood cells count, blood chemistry tests and liver function tests.
Other Diagnostic Studies
Antigen-capture enzyme-linked immunosorbent assay (ELISA) testing, IgM ELISA, polymerase chain reaction (PCR), and virus isolation can be used to diagnose a case of Ebola within a few days of the onset of symptoms. Persons tested later in the course of the disease or after recovery can be tested for IgM and IgG antibodies; the disease can also be diagnosed retrospectively in deceased patients by using immunohistochemistry testing, virus isolation, or PCR.[7]
Treatment
Medical Therapy
Ebola is potentially lethal and since no approved vaccine or treatment is available. Treatment is primarily supportive and includes maintaining fluids and electrolytes homeostasis, adequate oxygen levels and blood pressure and treating any complicating infections.[7] All patients with a confirmed or suspected viral hemorrhagic fever should be put in isolation and adequate contact precautions.[11]
Primary Prevention
Transmission of ebola virus disease has only been documented to occur during the symptomatic phase but not during the incubation period. If transmission of ebola occurs, steps need to be taken to prevent further infection as well as transmission to other people. It is important to be able to prevent subsequent transmission of ebola. Transmission of ebola can be prevented by isolation of patient, wearing a HEPA or other biosafety mask and by limiting the movement of the patient from the room to other areas.
Future or Investigational Therapies
There are promising results for antisense prevention therapies in monkey studies. Administration of an inhibitor of coagulation (rNAPc2) has demonstrated some benefit in monkey studies. There are non-conclusive results in human survivors from post-exposure vaccination, passive immunization with blood or serum or with recombinant human monoclonal antibodies.
References
- ↑ "Ebola Cases and Outbreaks - CDC Special Pathogens Branch". Centers for Disease Control and Prevention. Retrieved 2007-12-08.
- ↑ Bardi, Jason Socrates (2002). "Death Called a River". Scribbs Research Institute. 2 (1). Retrieved 2006-12-08.
- ↑ Ryabchikova E, Kolesnikova L, Smolina M, Tkachev V, Pereboeva L, Baranova S; et al. (1996). "Ebola virus infection in guinea pigs: presumable role of granulomatous inflammation in pathogenesis". Arch Virol. 141 (5): 909–21. PMID 8678836.
- ↑ Bray M, Davis K, Geisbert T, Schmaljohn C, Huggins J (1998). "A mouse model for evaluation of prophylaxis and therapy of Ebola hemorrhagic fever". J Infect Dis. 178 (3): 651–61. PMID 9728532.
- ↑ Connolly BM, Steele KE, Davis KJ, Geisbert TW, Kell WM, Jaax NK; et al. (1999). "Pathogenesis of experimental Ebola virus infection in guinea pigs". J Infect Dis. 179 Suppl 1: S203–17. doi:10.1086/514305. PMID 9988186.
- ↑ Bray M, Hatfill S, Hensley L, Huggins JW (2001). "Haematological, biochemical and coagulation changes in mice, guinea-pigs and monkeys infected with a mouse-adapted variant of Ebola Zaire virus". J Comp Pathol. 125 (4): 243–53. doi:10.1053/jcpa.2001.0503. PMID 11798241.
- ↑ 7.0 7.1 7.2 7.3 7.4 "Infection Control for Viral Haemorrhagic Fevers in the African Health Care Setting" (PDF).
- ↑ Feldmann, Heinz; Geisbert, Thomas W (2011). "Ebola haemorrhagic fever". The Lancet. 377 (9768): 849–862. doi:10.1016/S0140-6736(10)60667-8. ISSN 0140-6736.
- ↑ Formenty, Pierre; Hatz, Christophe; Le Guenno, Bernard; Stoll, Agnés; Rogenmoser, Philipp; Widmer, Andreas (1999). "Human Infection Due to Ebola Virus, Subtype Côte d'Ivoire: Clinical and Biologic Presentation". The Journal of Infectious Diseases. 179 (s1): S48–S53. doi:10.1086/514285. ISSN 0022-1899.
- ↑ Gradon J (2000). "An outbreak of Ebola virus: lessons for everyday activities in the intensive care unit". Crit Care Med. 28 (1): 284–5. PMID 10667555.
- ↑ Feldmann H, Geisbert TW (2011). "Ebola haemorrhagic fever". Lancet. 377 (9768): 849–62. doi:10.1016/S0140-6736(10)60667-8. PMC 3406178. PMID 21084112.