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Ebola Virus Disease : Causes & Prevention

Key facts:

  • Ebola virus disease (EVD), formerly known as Ebola haemorrhagic fever, is a severe, often fatal illness in humans.
  • EVD outbreaks have a case fatality rate of up to 90%.
  • EVD outbreaks occur primarily in remote villages in Central and West Africa, near tropical rainforests.
  • The virus is transmitted to people from wild animals and spreads in the human population through human-to-human transmission.
  • Fruit bats of the Pteropodidae family are considered to be the natural host of the Ebola virus.
  • Severely ill patients require intensive supportive care. No licensed specific treatment or vaccine is available for use in people or animals.

Ebola first appeared in 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.

Genus Ebolavirus is 1 of 3 members of the Filoviridae family (filovirus), along with genus Marburgvirus and genus Cuevavirus. Genus Ebolavirus comprises 5 distinct species:

  •     Bundibugyo ebolavirus (BDBV)
  •     Zaire ebolavirus (EBOV)
  •     Reston ebolavirus (RESTV)
  •     Sudan ebolavirus (SUDV)
  •     Taï Forest ebolavirus (TAFV).

BDBV, EBOV, and SUDV have been associated with large EVD outbreaks in Africa, whereas RESTV and TAFV have not. The 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 to date.

Signs and symptoms

EVD is a severe acute viral illness 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 definitively 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.

Source: WHO

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