Ebola Term paper

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The Ebola Virus is the common name for several strains of virus, three of which

are known to cause hemorrhagic fever in humans, which is characterized by massive

bleeding and destruction of internal tissues. Named for the Ebola River in Zaire, Africa,

where the virus was first identified, the Ebola virus belongs to the family Filoviridae.

Three strains of Ebola virus that are often fatal to humans have been identified. Named

for the areas in which the first recognized outbreaks took place, these strains are referred

to as Ebola/Zaire (EBOZ), Ebola/Sudan (EBOS), and Ebola/Tai Forest (EBOT). A fourth

Ebola strain, called Ebola/Reston(EBOR), has not been found to cause disease in

humans. As outbreaks of Ebola hemorrhagic fever continue to occur, other strains may be

identified. The viruses are long rods, 800 to 1000 nanometers (nm) long (1 nm equals

one-billionth of a meter, or 4 x 10-8 in), but particles as long as 14,000 nm have been

seen. Each virus consists of a coiled strand of ribonucleic acid (RNA) contained in an

envelope derived from the host cell membrane that is covered with 7 nm spikes placed 10

nm apart visible on the surface of the virion . When magnified several thousand times by

an electron microscope, these viruses have the appearance of long filaments or threads

but the particles are pleomorphic, meaning they can exist in many shapes. Their basic

structure is long and filamentious, essentially bacilliform, but the viruses often takes on a

"U" shape . They contain a unique single-stranded molecule of noninfectious (negative

sense ) RNA. The virus is composed of 7 polypeptides, a nucleoprotein, a glycoprotein, a

polymerase and 4 other undesignated proteins. Proteins are produced from

polyadenylated monocistronic mRNA a species transcribed from vi genomes. As the

infection progresses the cytoplasm of the infected cell develops "prominent inclusion

bodies" which contains the viral nucelocapsid, which will become highly structured. The

virus then assembles, and buds off the host cell, attaining its lipoprotein coat from the

infected cell's outer membrane. The replication in and destruction of the host cell is rapid

and produces a large number of viruses budding from the cell membrane. Symptoms

Cases of Ebola have occurred in isolated instances and in outbreaks in sub-Saharan

Africa. A significant problem in diagnosing the disease is that the viruses often strike in

remote areas of developing countries, where access to laboratories for specimen analysis

is limited. Of all the Ebola strains, Ebola/Zaire is the most dramatic and deadly. The

Ebola virus causes hemorrhagic fever, which is characterized by such symptoms as

severe headache, weakness, and muscle aches, followed by vomiting, abdominal pain,

diarrhea, inflammation of the throat (pharyngitis), inflammation of the mucous

membranes in the eye (conjunctivitis), and bleeding from body openings. The virus

spreads through the blood and is replicated in many organs. The histopathologic change

is focal necrosis in these organs, including the liver, lymphatic organs, kidneys, ovaries

and testes. The central lesions appear to be those affecting the vascular endothelium and

the platelets. The resulting manifestations are bleeding, especially in the muc usually

seven to ten days. The mortality rates in the known outbreaks have been 60% with

Ebola/Sudan virus and 77 to 88 percent with Ebola/Zaire virus. Although it is believed

that death results directly from the damage to internal tissues, it is not known why some

patients manage to survive the disease. There are no proven therapeutic drugs to treat

Ebola hemorrhagic fever, and treatment currently consists of preventing shock and

providing supportive care. Medical care is complicated by the need to protect medical

and nursing personnel. Convalescence is slow, often taking five weeks or more, and is

marked by weight loss and amnesia in the early stages of recovery. Currently, there is

little hope of developing a vaccine against the Ebola virus. Near the end of one outbreak

in Zaire during 1995, blood from convalescent patients was transfused into severely ill

victims in an attempt to transfer antibodies and T-lymphocytes (one type of white blood

cell) that might neutralize the Ebola virus and destroy infected cells. This procedure met

with some success, but carefully controlled trials must be conducted to confirm the safety

and effectiveness of this method. Evolution Besides morphological and biochemical

similarities, all nonsegmented negative-strand RNA viruses share several features in their

mechanisms of transcription and replication: similar genome organization,

complementarity of the genome extremities, homologous sequences in the 3' untranslated

region, conserved transcriptional signals, interruption of genes by intergenic sequences,

possession of a virion-associated polymerase, helical nucleocapsid as the functional

template for synthesis of replicative and messenger RNA, replication by synthesis of a

full-length antigenome, transcription of messenger RNAs by sequential interrupted

synthesis from a single promotor, transcription and replication in the cytoplasm, and

maturation by envelopment of independently assembled nucleocapsids at membrane sites

containing inserted viral proteins. These data suggest that all nonsegmented

negative-strand RNA viruses are derived from a common progenitor and support the

classification of the families Filoviridae, Paramyxoviridae and Rhabdoviridae in the

order Mononegavirales . In addition, comparative amino acid sequence analyses of

nucleoproteins and polymerase proteins suggest that filoviruses are more closely related

to paramyxoviruses than to rhabdoviruses. History of Ebola Outbreaks Ebola virus was

identified for the first time in 1976, when two epidemics of hemorrhagic fever occurred,

one in Zaire, the other 600 km distant in Sudan. The combined outbreaks accounted for

more than 550 cases and 430 deaths. A third strain of the Ebola virus was identified in

1989 in a quarantine facility in Reston, Virginia, where hundreds of imported Philippine

monkeys died. The Ebola/Reston virus seems not to cause disease in humans-although

four laboratory technicians were infected with the virus, none of them became ill.

Another large epidemic of Ebola hemorrhagic fever occurred in Zaire, this time in and

around the city of Kikwit during the summer of 1995, infecting 315 people and killing

242. The strains of Ebola virus isolated in Zaire in 1976 and 1995, 19 years and 500 km

apart, are virtually identical. A single nonfatal case of Ebola hemorrhagic fever occurred

in late 1994 in Cte d'Ivoire. A Swiss zoologist who performed an autopsy on a

chimpanzee was infected by the virus, which was subsequently identified as the fourth

strain, Ebola/Tai Forest, named for the Tai Forest in the Cte d'Ivoire. Since the first

episode there have been additional cases and fatalities caused by this virus, in Cte

d'Ivoire, Liberia, and Gabon. Diagnosing the Virus Each outbreak has been traced to an

index case, an infected person who came into contact with a reservoir host, an animal or

arthropod involved in the life cycle of the virus. Of all the disease-causing human

viruses, the Ebola and its relative Marburg, which also causes hemorrhagic fever, are the

only ones remaining for which the original host and the natural transmission cycle remain

unknown. It is not known whether monkeys serve as hosts or if other mammals, birds,

reptiles, or even mosquitoes or ticks are involved. *From the index case, infection

between humans is principally due to direct, close contact, such as that between a patient

and nurses and doctors. Unhygienic hospital conditions also spread the virus. The disease

is diagnosed using a laboratory technique called ELISA (enzyme-linked immunosorbant

assay) that searches for specific antigens (viral proteins) or antibodies made by the

infected patient. The test is performed on a monolayer of infected and uninfected cells

fixed on a microscopic slide. IgG- or IgM-specific...

bjach.polk.amedd.army.mil/B8/Ebola.htm. Ebola
galaxy.einet.net/galaxy/medicine/Diseases-and-Disorders/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
www.bocklabs.wisc.edu. Marburg and Ebola Viruses
www.cdc.gov. Centers for Disease Control and Prevention. February 5, 1997
www.infowire.vet/brett/personal/eframe.html Ebola Page
www.outbreak.com. The Outbreak You should cite this paper as follows:

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