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... freshly collected. A technique used to duplicate genetic material for study, called the polymerase chain reaction, is used to detect Ebola viral material in patient blood or tissues. When infection by the virus is suspected, local health officials institute strict barrier nursing procedures (such as the use of gowns, gloves, and masks) and usually call on experts from the World Health Organization (WHO), the Centers for Disease The Ebola virus has been classified by the CDC as Biosafety Level 4, which requires the greatest safety precautions. To ensure maximum safety, virologists must work in special protective clothing, and their laboratories contain equipment that sterilizes air, and liquid and solid wastes. Detailed studies comparing RNA sequences between the different viral strains are only now being performed.
It is hoped that such genetic information will provide clues about the natural history and hosts of the viruses. Natural Reservoir The natural reservoir of the Ebola virus is not entirely known. Serological studies suggest that Ebola or related viruses are endemic in Zaire, Sudan, the Central African Republic, Gabon, Nigeria, Ivory Coast, Liberia, Cameroon and Kenya. The geographic range of Ebola strains may extend to other African countries, for which adequate survey is lacking.
Extensive ecological studies are currently underway in Cte d'Ivoire, Gabon and Zaire to pinpoint the reservoir. Ebola-related filo viruses were isolated from cynomolgus monkeys (Malacca fascicularis) imported into the United States of America from the Philippines in 1989. A number of the monkeys died and at least four persons were infected, although none of them suffered clinical illness. Analysis of Outbreaks Serologic evidence has suggested the presence of Ebola virus in Gabon since 1982. Since late 1994, three apparently independent outbreaks of Ebola virus hemorrhagic fever have occurred among humans in northeastern Gabon, in the forested areas of equatorial Boou-Ivindo province. The first, which started in December 1994 in gold-paper encampments of far northeastern Gabon, in the Minkouka area near the Nouna River, had several laboratory-confirmed cases.
The second, which began in early February 1996 in Mayibout village on the Ivindo River, resulted in 37 Ebola hemorrhagic fever cases. The only means of transportation between these two areas is by boat; Makokou, the closest town to them, has the provincial hospital to which patients and contacts were transferred. The third outbreak, started in July 1996 in the village of Book, where most of the cases occurred; however, scattered cases have been diagnosed in surrounding villages and towns. Some patients have even been transported to Libreville, probably during the incubation period of the disease. One patient was treated in South Africa, where a fatal nosocomial infection was subsequently reported in a health care worker; over 43 deaths due to Ebola hemorrhagic fever were reported during this prolonged outbreak. There were many gene sequences obtained from human samples during each of the three Gabonese epidemics.
Some was obtained from blood collected 1 day before the death of a patient, from the Nouna area, during the 1994 outbreak. Other sequences were derived from blood collected during the spring 1996 outbreak, from two primary patients who were infected while butchering a chimpanzee they found dead in the forest. One sequence was derived from blood collected from what appears to have been a secondary case during the same outbreak; the patient was probably infected by contact with one of the index patients while visiting a traditional doctor who lived near Mayibout village. The isolation of Ebola virus in a cell culture from human blood samples collected during the three different outbreaks was easily accomplished in a single passage. RNA was extracted from blood or primary tissue culture samples by using a commercial kit. Viral sequences were amplified from RNA by using the reverse transcriptase-polymerase chain reaction technique.
Briefly, amplified products were subjected to agarose electrophoresis and were stained and visualized with ethidium bromide; DNA bands were then excised and extracted. In some cases, nested PCR with internal primers was performed, using first-round products. Amplified products were directly sequenced by using an automated non isotopic method. Excess dye-labeled dideoxynucleotide terminators were removed, and reaction products were analyzed.
A consensus sequence was established by aligning all the Ebola from Gabon, the Zaire 1976 and 1995 Ebola virus sequences, as well as the sequence of the virus obtained from a nurse in South Africa who was infected of the three different outbreaks in Gabon. Although the viruses causing the Gabonese outbreaks clearly belong to the Zaire subtype, they were distinct from viruses that had caused disease in Zaire. No differences were observed between tissue-culture-passage and clinical-material-derived sequences or between primary or secondary case sequences. RNA extracted from a single representative of each outbreak was then used to generate the entire gene sequence for the Gabon Ebola viruses. The gene sequence from the Gabon spring 1996 viruses differed from the sequence of the Gabon fall 1994 viruses by four nucleotides. The genetic sequence from the Gabon fall 1996 viruses differed from the sequence of the Gabon spring 1996 virus by four additional nucleotides.
A single most parsimonious tree was obtained (Figure 4), and bootstrap analysis strongly supports a common evolutionary origin for the viruses associated with disease in Gabon and Zaire. Overall, these data indicate that the three Gabon outbreaks should be considered independent events, likely originating from different sources. The presence of stable virus sequences and the lack of genetic variability between strains isolated within an outbreak was previously seen during the outbreak of Ebola hemorrhagic fever in Kikwit, Zaire, in 1995, and despite the small number of isolates tested, is again suggested in Gabon. During a 20 -month period, Gabon had three different outbreaks of Ebola virus hemorrhagic fever. The first and the second episodes apparently started during the rainy season (December and February), while the third began during the dry season (July).
The deaths of nonhuman primates were associated with all three outbreaks. Minkouka area inhabitants reported finding dead chimpanzees and gorillas in the forest during the fall of 1994. All the primary human patients in the spring 1996 outbreak were infected while butchering dead chimpanzees. For the third outbreak, the investigation has indicated an index patient who was a hunter, living in a forest camp in the Book area. During the same period, an Ebola virus-infected dead ch In Cte d'Ivoire in 1994, an investigator was infected with Ebola virus while performing necropsy on a dead chimpanzee. Primates are unlikely to be the reservoir of Ebola virus since experimental or natural infection is quickly fatal.
A better knowledge of the ecology of great apes, particularly their food preferences and habitats, may lead to the identification of the virus reservoir. Gabon's equatorial forests, where three independent outbreaks have occurred in less than 3 years, offer an excellent opportunity for these investigations. It has now become apparent that the only solution to this problem, which society is increasingly becoming aware of, is diligent research and experimentation. The CDC continues to inject infant mice and guinea pigs with the virus and document the details of either their deaths or recoveries. It is the hopes of both the scientific community and the rest of the world that some tangible solution be found as Bibliography: Bibliography back. polk.
add. army. mil/B 8 /Ebola. htm.
Ebola galaxy. eight. net / galaxy /medicine/Diseases-and-Diso riders/Viruses-Diseases/RNA-Virus-I infections/Ebola-Hemorrhagic-Fever. html. RNA Virus Infections Microsoft Encarta Encyclopedia 97 Ebola Star and Taggart.
Biology: The Unity and Diversity of Life. Wadsworth. Toronto. 1998 web Marburg and Ebola Viruses web Centers for Disease Control and Prevention. February 5, 1997 web Ebola Page web The Outbreak
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Research essay sample on Ebola Hemorrhagic Fever Centers For Disease
