Saturday, August 30, 2014

The Ebola virus disease: classification and naming of a group of zoonotic filoviruses

Are viruses of the Ebola type going to cause the next big human pandemic? So far, the Ebola virus disease, an often fatal illness, has affected local groups of humans, gorillas and other mammals in tropical Africa. Some regional populations of gorillas have disappeared. Ebola viruses are zoonotic: they can move from one species to certain others. For example, humans are susceptible to Ebola, horses are not. Intervals of hiding—times free of infection events—are followed by sudden outbreaks.

Recent news about human-to-human transmission of Ebola viruses in West and Central Africa are alarming. Much about Ebola is not yet understood. Fruit bats of the Pteropodidae family are considered as a key reservoir hosts for the virus, spreading it over long distances. But modern air travel and animal trading can result in outbreaks around the globe at any time. No proven vaccine is yet available [1-4].

Major symptoms of an Ebola infection include abdominal pain, fever, headache, sore throat, nausea, vomiting, loss of appetite, arthralgia (joint pain), myalgia (muscule pain), asthenia (weakness), tachypnea (rapid breathing), conjunctival injection (pink eyes) and diarrhea. Like some other viruses, ebolaviruses suppress the immune system  (see pages 94 and 95 in [1]).

The Ebola virus disease is named after the Ebola River in the Democratic Republic of the Congo (formerly Zaire). In 1976, an Ebola outbreak (Zaire outbreak) occurred in a small Catholic mission hospital in Yambuka, a village in the Bumba Zone district (page 69 in [1]). Today, five species of ebolaviruses are known. They all are named after the area or place at which they were first observed and documented. The following overview is based on the scientifically focused, excellently researched and fascinatingly written thriller Spillover by David Quammen [1].

Zaire ebolavirus (EBOV)
The Zaire ebolavirus is named after the Zaire outbreak mentioned above. The case fatality rate was 88 percent; lower than for untreated rabies cases, but higher than for any other recorded outbreak (see page 71 in [1]).

Sudan ebolavirus (SUDV)
This virus is named after an Ebola disease outbreak in southern Sudan in 1976, causing 151 deaths—a lethality lower than in the Zaire outbreak (see page 76 in [1]).

Reston virus (RESTV)
The Reston virus—probably native to the Philippines—is named after a lab-animal quarantine facility in suburban Reston across the Potomac River from Washington, DC. In 1989, an Ebola outbreak occurred at this facility, known as the Reston Primate Quarantine Unit, among long-tailed macaques (Macaca fascicularis), which were imported from the Philippines for medical research (see pages 77 and 78 in [1]). No illness or death in humans from this species has been reported to date [2].

Taï Forest virus (TAFV)
This virus is named after the Taï Forest National Park in Côte d'Ivoire (Ivory Coast in West Africa), near this country's border with Liberia. In 1992, Christophe Boesch, a Swiss biologist, got infected with Ebola during a necropsy of a dead chimpanzee. Quickly hospitalized and treated in Switzerland, she survived (see page 80 in [1]). 

Bundibugyo virus (BDBV)
The Bundibugyo virus emerged in late 2007 as the fifth ebolavirus species. Twenty people died in a remote mountain region in Uganda. Blood samples flown to the CDC in Atlanta revealed an Ebola-type virus, one that genetically was at least 32 percent different from any of the other four (see page 84 in [1]).

The often-used term “Ebola hemorrhagic fever” (EHF) is a misnomer for Ebola virus disease: many Ebola patients do not show any bleeding at all.

Ebolaviruses, like the Marburg virus, were originally classified as filoviruses (a genus), but are now grouped into the Filoviridae family encompassing the two genera of Ebola-like and Marburg-like viruses.

Keywords: field biology, virology, pathology, taxonomy, terminology, zoonosis, Ebola symptoms.

References and more to learn
[1] David Quamman: Spillover. Animal Infections and the next human pandemic. W. W. Norton & Company, New York and London, 2012.
[2] World Health Organization: Ebola virus disease.
[3] J. H. Kuhn et al.: Proposal for a revised taxonomy of the family Filoviridae: classification, names of taxa and viruses, virus abbreviations. Arch. Virol. 2010, 155 (12), pp. 2083-2103. DOI: 10.1007/s00705-010-0814-x.
[4] Tara's Ebola Site: Ebola Classification and Taxonomy.

1 comment:

  1. Ebola is like terrorism. It's "new" and foreign and scary as hell, even though you have a higher chance of dying from bee stings or lightning strikes than Ebola or terrorism. And these issues get a LOT more coverage from the media than the old fashioned killers. It's interesting the way we process risk management.
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