Ebola causes

style="background:#Template:Taxobox colour;"|Ebola virus
style="background:#Template:Taxobox colour;" | Virus classification
Group: Group V ((-)ssRNA) Order: Mononegavirales Family: Filovirus Genus: Ebolavirus
Type species
Zaïre Ebolavirus
Species
Reston Ebolavirus Sudan Ebolavirus Ivory Coast Ebolavirus Bundibugyo Ebolavirus

Ebola Microchapters
Home
Patient Information
Overview
Historical Perspective
Classification
Pathophysiology
Causes
Differentiating Ebola from other Diseases
Epidemiology and Demographics
Risk Factors
Screening
Natural History, Complications and Prognosis
Diagnosis
Algorithm for the Evaluation of the Returned Traveler
Emergency Department Evaluation
Case Definition
History and Symptoms
Physical Examination
Laboratory Findings
Other Diagnostic Studies
Treatment
Medical Therapy
Hospital Preparedness
Checklists
Air Medical Transport
Monitoring and Movement Following Exposure
Primary Prevention
Future or Investigational Therapies
Postmortem Care
Postmortem Care
Case Studies
Case #1
Ebola causes On the Web
Most recent articles
Most cited articles
Review articles
CME Programs
Powerpoint slides
Images
American Roentgen Ray Society Images of Ebola causes All Images X-rays Echo & Ultrasound CT Images MRI
Ongoing Trials at Clinical Trials.gov
US National Guidelines Clearinghouse
NICE Guidance
FDA on Ebola causes
CDC on Ebola causes
Ebola causes in the news
Blogs on Ebola causes
Directions to Hospitals Treating ebola
Risk calculators and risk factors for Ebola causes

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Ebola infection is caused by a virus that belongs to the family Filoviridae. Four viral subtypes have been reported to cause clinical illness in humans: Bundibugyo ebolavirus, Sudan ebolavirus, Tai Forest ebolavirus, and Zaire ebolavirus.

Taxonomy

Viruses; ssRNA viruses; ssRNA negative-strand viruses; Mononegavirales; Filoviridae; Ebolavirus

• Ebolavirus

• Bundibugyo ebolavirus
• Reston ebolavirus

• Reston ebolavirus - Reston
• Reston ebolavirus - Reston (1989)
• Reston ebolavirus - Siena/Philippine-92

• Sudan ebolavirus

• Sudan ebolavirus - Boniface (1976)
• Sudan ebolavirus - Maleo (1979)
• Sudan ebolavirus - Nakisamata
• Sudan ebolavirus - Uganda (2000)

• Tai Forest ebolavirus

• Tai Forest virus - Côte d’Ivoire, Côte d’Ivoire, 1994

• Zaire ebolavirus

• Ebola virus - Mayinga, Zaire, 1976
• Zaire ebolavirus - Eckron (Zaire, 1976)
• Zaire ebolavirus - Gabon (1994-1997)
• Zaire ebolavirus - Zaire (1995)

• Unclassified Ebolavirus

• Ebola virus Yambio0401
• Ebola virus Yambio0402
• Ebola virus Yambio0403
• Ebola virus sp.

Biology

Ebola infection is caused by a virus that belongs to the family Filoviridae. Four viral subtypes have been reported to cause clinical illness in humans: Bundibugyo ebolavirus, Sudan ebolavirus, Tai Forest ebolavirus, and Zaire ebolavirus. The human disease has so far been limited to parts of Africa. A very small number of people in the United States and in the Philippines were infected with the fifth type of the virus, known as Reston ebolavirus, and did not develop any signs of disease. The virus can be passed to humans from infected animals and animal materials. Ebola can also be spread among humans by close contact with infected body fluids or by infected needles.

Structure

Size and Shape

Electron micrographs of members of Ebola virus show them to have the characteristic thread-like structure of a filovirus. EBOV VP30 is around 288 amino acids long. The virions are tubular and variable in shape and may appear as a "U", "6", coiled, circular, or branched shape, however, laboratory purification techniques, such as centrifugation, may contribute to the various shapes. Virions are generally 80 nm in diameter. They are variable in length, and can be up to 1400 nm long. On average, however, the length of a typical Ebola virus is closer to 1000 nm. In the center of the virion is a structure called nucleocapsid, which is formed by the helically wound viral genomic RNA complexed with the proteins NP, VP35, VP30 and L. It has a diameter of 40 – 50 nm and contains a central channel of 20–30 nm in diameter. Virally encoded glycoprotein (GP) spikes 10 nm long and 10 nm apart are present on the outer viral envelope of the virion, which is derived from the host cell membrane. Between envelope and nucleocapsid, in the so-called matrix space, the viral proteins VP40 and VP24 are located.

Genome

Each virion contains one minor molecule of linear, single-stranded, negative-sense RNA, totaling 18959 to 18961 nucleotides in length. The 3′ terminus is not polyadenylated and the 5′ end is not capped. It was found that 472 nucleotides from the 3' end and 731 nucleotides from the 5' end were sufficient for replication. It codes for seven structural proteins and one non-structural protein. The gene order is 3′ - leader - NP - VP35 - VP40 - GP/sGP - VP30 - VP24 - L - trailer - 5′; with the leader and trailer being non-transcribed regions which carry important signals to control transcription, replication and packaging of the viral genomes into new virions. The genomic material by itself is not infectious, because viral proteins, among them the RNA-dependent RNA polymerase, are necessary to transcribe the viral genome into mRNAs, as well as for replication of the viral genome.

Life Cycle

• Virus attaches to host receptors through the GP (glycoprotein) surface peplomer and is endocytosed into vesicles in the host cell.
• Fusion of virus membrane with the vesicle membrane occurs; nucleocapsid is released into the cytoplasm.
• The encapsidated, negative-sense genomic ssRNA is used as a template for the synthesis (3' - 5') of polyadenylated, monocistronic mRNAs.
• Translation of the mRNA into viral proteins occurs using the host cell's machinery.
• Post-translational processing of viral proteins occurs. GP0 (glycoprotein precursor) is cleaved to GP1 and GP2, which are heavily glycosylated. These two molecules assemble, first into heterodimers, and then into trimers to give the surface peplomers. SGP (secreted glycoprotein) precursor is cleaved to SGP and delta peptide, both of which are released from the cell.
• As viral protein levels rise, a switch occurs from translation to replication. Using the negative-sense genomic RNA as a template, a complementary +ssRNA is synthesized; this is then used as a template for the synthesis of new genomic (-)ssRNA, which is rapidly encapsidated.
• The newly-formed nucleocapsides and envelope proteins associate at the host cell's plasma membrane; budding occurs, and the virions are released

Scientists have identified four types of the Ebola virus. Three 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. The disease can be passed to humans from infected animals and animal materials. Ebola can also be spread between humans by close contact with infected bodily fluids or through infected needles in the hospital.

Viral Reservoirs

Despite numerous studies, the wildlife reservoir of Ebolavirus has not been identified. Between 1976 and 1998, from 30,000 mammals, birds, reptiles, amphibians, and arthropods sampled from outbreak regions, no Ebolavirus was detected apart from some genetic material found in six rodents (Mus setulosusand Praomys species) and a shrew (Sylvisorex ollula) collected from the Central African Republic in 1998. Ebolavirus was detected in the carcasses of gorillas, chimpanzees and duikers during outbreaks in 2001 and 2003 (the carcasses were the source of the initial human infections) but the high mortality from infection in these species precludes them from acting as reservoirs. Plants, arthropods, and birds have also been considered as reservoirs, however bats are considered the most likely candidate. Bats were known to reside in the cotton factory in which the index cases for the 1976 and 1979 outbreaks were employed and have also been implicated in Marburg infections in 1975 and 1980. Of 24 plant species and 19 vertebrate species experimentally inoculated with Ebolavirus, only bats became infected. The absence of clinical signs in these bats is characteristic of a reservoir species. In 2002-03, a survey of 1,030 animals from Gabon and the Republic of the Congo including 679 bats found Ebolavirus RNA in 13fruit bats (Hyspignathus monstrosus, Epomops franquetti and Myonycteris torquata). Bats are also known to be the reservoirs for a number of related viruses including Nipah virus, Hendra virus andlyssaviruses.

Microscopic Pathology

The images below display key features of the Ebola virus.

• 

  This transmission electron micrograph (TEM) demonstrates the ultrastructural morphology displayed by an Ebola virus. Source: CDC microbiologist Frederick A. Murphy.Adapted from Public Health Image Library (PHIL), Centers for Disease Control and Prevention.

• 

  This transmission electron micrograph (TEM) demonstrates the ultrastructural morphologic changes in this tissue sample isolate.Adapted from Public Health Image Library (PHIL), Centers for Disease Control and Prevention.

• 

  Scanning electron micrograph (SEM) revealing ultrastructural morphologic features of the Ebola virus from the Ivory Coast of Africa.Adapted from Public Health Image Library (PHIL), Centers for Disease Control and Prevention.

• 

  Negatively-stained transmission electron micrograph (TEM) demonstrating the ultrastructural curvilinear morphologic features displayed by the Ebola virus from the Ivory Coast of Africa.Adapted from Public Health Image Library (PHIL), Centers for Disease Control and Prevention.