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What is Ebola Virus Disease

WHAT IS EBOLA VIRUS DISEASE

What is Ebola virus Disease

EBOLA VIRUS

HISTORY OF EBOLA VIRUS DISEASE:

Ebola virus disease (EVD) was first found in the year 1976 in 2 simultaneous outbreaks, in Nzara, Sudan, and in Yambuku, Democratic Republic of Congo. The latter was in a village situated near the Ebola River, from which the disease takes its name.

  • The first outbreak occurred on 26 August 1976 in Yambuku, Democratic Republic of Congo.
  • The first recorded case was Mabalo Lokela, a 44‑year-old schoolteacher.
  • This virus was renamed to “Ebola virus” in 2010 to avoid confusion.
  • Earlier abbreviations for the virus were EBOV-Z (for Ebola virus Zaire) and most recently ZEBOV (for Zaire Ebola virus or Zaire ebolavirus).
  • In 2010, EBOV was reinstated as the abbreviation for the virus.

Ebola virus (EBOV) is the only member of the Zaire ebolavirus species. Ebola virus disease (EVD) was formerly known as Ebola haemorrhagic fever. It is often fatal in humans. The Ebola virus is one of the dangerous viruses. The virus and its species were both originated and known in Zaire, the country which is now known by the name Democratic Republic of Congo. In this country, it was first suspected to be a new virus of the closely related Marburg virus. Ebolavirus is a zoonotic pathogen.

Earlier Ebola virus disease outbreaks occured primarily in remote villages in Central and West Africa, near tropical rainforests. Now it is found widely in countries such as Nigeria, Liberia, Sierra Leone, Guinea Congo and Sudan,. Earlier these outbreaks have a case fatality rate of up to 90%. At present in the year 2014, the fatality rate is 55%. The virus is transmitted to people from wild animals and spreads in the human population. Fruit bats of the Pteropodidae family are considered to be the natural host of the Ebola virus. The symptoms resembled malaria, and subsequent patients received quinine. Transmission has been attributed to reuse of unsterilized needles and close personal contact.

No licensed specific treatment or vaccine is available for use in people or animals. However, now Canada with the assistance of National Microbiology lab claim to have found the vaccine and medicine for this Ebola Virus, which is named as VSV-EBOV.

Genus Ebolavirus is one of the three members of the Filoviridae family (filovirus), along with genus Marburgvirus and genus Cuevavirus. Genus Ebolavirus comprises 5 distinct species namely :

  • (1) Bundibugyo ebolavirus (BDBV)
  • (2) Zaire ebolavirus (EBOV)
  • (3) Reston ebolavirus (RESTV)
  • (4) Sudan ebolavirus (SUDV)
  • (5) Taï Forest ebolavirus (TAFV).

Bundibugyo ebolavirus (BDBV), Zaire ebolavirus (EBOV), and Sudan ebolavirus(SUDV) have been associated with large Ebola virus disease outbreaks in Africa, whereas Reston ebolavirus (RESTV) and Taï Forest ebolavirus (TAFV) have not. The Reston ebolavirus (RESTV) species, found in Philippines and the People’s Republic of China, can infect humans, but no illness or death in humans from this species has been reported. It has a genome with two or three gene overlaps (VP35/VP40, GP/VP30, VP24/L) and has a genomic sequence that differs from the type virus by less than 30%

GENOME OF EBOLA VIRUS:

Each virion contains one molecule of linear, single-stranded, negative-sense RNA, 18,959 to 18,961 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 are 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 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, because it is a negative sense RNA virus, as well as for replication of the viral genome. Sections of the NP and the L genes from filoviruses have been identified as endogenous in the genomes of several groups of small mammals.

STRUCTURE OF EBOLA VIRUS:

The structure of Ebola virus carries a negative-sense RNA genome in virions which are cylindrical/tubular. It contains viral envelope, matrix, and nucleocapsid components. The overall cylinders are generally approx. 80 nm in diameter, and having a virally encoded glycoprotein (GP) projecting as 7-10 nm long spikes from its lipid bilayer surface. The cylinders are of variable length, normally 800 nm, but sometimes up to 1000 nm long. The outer viral envelope of the virion is derived by budding from domains of host cell membrane into which the GP spikes have been inserted during their biosynthesis. Individual GP molecules appear with spacings of about 10 nm. Viral proteins VP40 and VP24 are located between the envelope and the nucleocapsid in the matrix space. At the center of the virion structure is the nucleocapsid, which is composed of a series of viral proteins attached to a 18–19 kb linear, negative-sense RNA without 3′-polyadenylation or 5′-capping. The RNA is helically wound and complexed with the NP, VP35, VP30, and L proteins. The helix has a diameter of 80 nm and contains a central channel of 20–30 nm in diameter.

The overall shape of the virions after purification and visualization (e.g., by ultracentrifugation and electron microscopy, respectively) varies considerably; simple cylinders are far less prevalent than structures showing reversed direction, branches, and loops (i.e., U-, shepherd’s crook-, 9- or eye bolt-shapes, or other or circular/coiled appearances), the origin of which may be in the laboratory techniques applied. The characteristic “threadlike” structure is, however, a more general morphologic characteristic of filoviruses (alongside their GP-decorated viral envelope, RNA nucleocapsid, etc.).

MODE OF TRANSMISSION OF EBOLA VIRUS

Ebola virus is introduced into the human population through close contact with the blood, secretions, organs or other bodily fluids of infected animals. In Africa, infection has been recorded through the handling of infected chimpanzees, gorillas, fruit bats, monkeys, forest antelope and porcupines found ill or dead or in the rainforest. Among this fruit bats are considered to be the main source of transmission.

Ebola virus then spreads in the community through human to human transmission, with infection resulting from direct contact through broken skin or through mucous membranes with the blood, secretions, organs or other bodily fluids of infected people, and indirect contact with environments contaminated with such fluids. Burial ceremonies in which mourners have direct contact with the body of the deceased person can also play a role in the transmission of Ebola virus. Men who have recovered from the disease can still transmit the virus through their semen for up to 7 weeks after recovery from illness.

Health-care workers have frequently been infected while treating patients with suspected or confirmed Ebola virus disease. This has occurred through close contact with patients when infection control precautions are not strictly practiced.

The only available evidence available comes from healthy adult males. It would be premature to extrapolate the health effects of the virus to all population groups, such as immuno-compromised persons, persons with underlying medical conditions, pregnant women and children.

The Ebola virus will not be transmitted through mosquitoes or insect-bites.

VULNERABILITY TO DISINFECTANTS:

Ebola virus is vulnerable to disinfectants such as sodium hypochlorite, lipid solvents, phenolic disinfectants, peracetic acid, methyl alcohol, ether, sodium deoxycholate, 2% glutaraldehyde, 0.25% Triton X-100, β-propiolactone, 3% acetic acid (pH 2.5), formaldehyde and paraformaldehyde, and detergents such as SDS (20, 21, 31-34).

Ebola virus are moderately sensitive to heat and can be inactivated by heating for 30 minutes to 60 minutes at 60ºC, boiling for 5 minutes, gamma irradiation (1.2 x106 rads to 1.27 x106 rads), and/or UV radiation (3, 6, 20, 32, 33). The virus can survive in liquid or dried material for a number of days

SIGNS AND SYMPTOMS OF EBOLA VIRUS DISEASE:

The signs and symptoms for Ebola virus disease are often characterized by the sudden onset of fever, intense weakness, muscle pain, headache and sore throat. This is followed by vomiting, diarrhoea, rash, impaired kidney and liver function, and in some cases, both internal and external bleeding. Laboratory findings include low white blood cell and platelet counts and elevated liver enzymes.

People are infectious as long as their blood and secretions contain the virus. Ebola virus was isolated from semen 61 days after onset of illness in a man who was infected in a laboratory.

The incubation period, that is, the time interval from infection with the virus to onset of symptoms, is 2 to 21 days.

DIAGNOSIS:

Other diseases that should be ruled out before a diagnosis of EVD can be made include: malaria, typhoid fever, shigellosis, cholera, leptospirosis, plague, rickettsiosis, relapsing fever, meningitis, hepatitis and other viral haemorrhagic fevers.

Ebola virus infections can be diagnosed in a laboratory through several types of tests:

  • antibody-capture enzyme-linked immunosorbent assay (ELISA)
  • antigen detection tests
  • serum neutralization test
  • reverse transcriptase polymerase chain reaction (RT-PCR) assay
  • electron microscopy
  • virus isolation by cell culture.

Samples from patients are an extreme biohazard risk; testing should be conducted under maximum biological containment conditions.

Table: Chronology of previous Ebola virus disease outbreaks

Year Country Ebolavirus species Cases Deaths Case fatality
2014 Guinea, Liberia, Sierra Leone, Nigeria as on13.08.2014 2127 1145 54%
2012 Democratic Republic of Congo Bundibugyo 57 29 51%
2012 Uganda Sudan 7 4 57%
2012 Uganda Sudan 24 17 71%
2011 Uganda Sudan 1 1 100%
2008 Democratic Republic of Congo Zaire 32 14 44%
2007 Uganda Bundibugyo 149 37 25%
2007 Democratic Republic of Congo Zaire 264 187 71%
2005 Congo Zaire 12 10 83%
2004 Sudan Sudan 17 7 41%
2003 (Nov-Dec) Congo Zaire 35 29 83%
2003 (Jan-Apr) Congo Zaire 143 128 90%
2001-2002 Congo Zaire 59 44 75%
2001-2002 Gabon Zaire 65 53 82%
2000 Uganda Sudan 425 224 53%
1996 South Africa (ex-Gabon) Zaire 1 1 100%
1996 (Jul-Dec) Gabon Zaire 60 45 75%
1996 (Jan-Apr) Gabon Zaire 31 21 68%
1995 Democratic Republic of Congo Zaire 315 254 81%
1994 Cote d’Ivoire Taï Forest 1 0 0%
1994 Gabon Zaire 52 31 60%
1979 Sudan Sudan 34 22 65%
1977 Democratic Republic of Congo Zaire 1 1 100%
1976 Sudan Sudan 284 151 53%
1976 Democratic Republic of Congo Zaire 318 280 88%

VACCINE AND TREATMENT FOR EBOLA VIRUS DISEASE

No licensed vaccine for EVD is available. Several vaccines are being tested, but none are available for clinical use. As of now 1000s of affected patients have died for this virus. However Canada claim to have vaccines for Ebola virus disease.

Patients are frequently dehydrated and require oral rehydration with solutions containing electrolytes or intravenous fluids. Severely ill patients require intensive supportive care.

No specific treatment is available and new drug therapies are being evaluated.

Now Canada with the assistance of its National Microbiology lab claim to have founded the vaccine and medicine for this Ebola Virus, which is named as VSV-EBOV. The WHO has also given recognition for this medicine and Canada had now sent 1000 doses to the affected country Liberia. ZMAPP- a medicine founded by U.S.A for curing Ebola Virus disease is also sent to Liberia.

World Bank has allotted $200 Million for developing medicine for Ebola virus disease.

PREVENTION AND CONTROL OF EBOLA VIRUS DISEASE

If an outbreak is suspected, the premises should be quarantined immediately. Culling of infected animals, with close supervision of burial or incineration of carcasses, may be necessary to reduce the risk of animal-to-human transmission. Restricting or banning the movement of animals from infected farms to other areas can reduce the spread of the disease.

No animal vaccine against RESTV is available. Routine cleaning and disinfection of pig or monkey farms (with sodium hypochlorite or other detergents) should be effective in inactivating the virus.

Patients should be carefully treated and their contact particularly with their bodily fluids, with other people should be avoided without safety measures.

Most of the Countries have set up information centres to know about the Ebola Virus disease and the Indian Government had set up 24 hours free telephone service to know about the Ebola virus disease : +91-011-2306149.

Source: WHO, Wikipedia

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