What’s in an ebolavirus name?

IMPORTED POST*

Virus taxonomy is the classification of viruses into groups based on similarities.

Today, classification is supported by viral gene and genome sequence information.

The International Committee on Taxonomy of Viruses (ICTV) takes care of the official virus taxonomy. It has a pretty friendly website with a good search engine, and the latest (2013 at writing) virus taxonomy can be found here. [1]

So what does it, and its tome, Virus Taxonomy, Ninth Report of the International Committee on Taxonomy of Viruses [2], have to say about ebolaviruses? Well, not as much as you might like, if you want to be able to name them, talk conversationally about them and discuss the issues around the disease resulting from infection by most of them. Sure, you can just call it all “Ebola” (which is a river in Africa by the way) and be done with it, but you’d be wrong. And some smart alec will correct you for sure. Here is where the ICTV Filoviridae Study Group fills in a lot of blanks.

One thing to get on top of first up. When talking or writing about these little pathogens, we can just call lump them together under the conversational term “ebolaviruses” thus…”Hey Jeanette, did you hear about the latest ebolavirus infection numbers over the weekend?” is a question that could refer to any of the 5 very different viruses.

So, let’s try to make that tearoom conversation a little more accurate.

The very dry, detailed stuff down to the level of a species

The italicisation and the capitalisation below are really important to taxonomy guys – so, ya know, care.

Also, the ICTV reminds us that the name of the species is not the name of a virus – they are 2 different things. The species is a broad term for all the measurably different viruses that exist in the wild. Here, species is to viruses what Mitsubishi Sigma is to identifying my old car. A virus name, e.g. Ebola virus (see below), is like identifying my car as “a silver 1989 Mitsubishi Sigma”.

The viruses we are talking about here belong to the order Mononegavirales, the family Filoviridae, and the genus Orthoebolavirus.

There are 6 species within the genus.[6]. The species names are in italics below. In brackets is the commonly used name of the virus (the virus belongs to the species container) and its abbreviation.

But what should I call the latest ebolavirus strain, variant, genotype, subtype, serotype, isolate thingy?

In the current outbreak, the latest virus is an Ebola virus (EBOV), which we can now say belongs to the species Zaire ebolavirus.

But back to the car analogy. The silver 1989 Mitsubishi Sigma name is still not enough to tell it apart from any other silver Mitsubishi Sigma parked at the same shopping centre. How do you choose yours in a way that won’t get you arrested for breaking into someone else’s car? They both look like silver Mitsubishi Sigmas. But the silver Mitsubishi Sigma with license plate ABC 321 is yours and yours alone, and that code differentiates your car from any other anywhere in the world.

We know from genome sequencing studies that the virus circulating in Guinea is an EBOV (a silver Mitsubishi Sigma) and is not identical to the one in (what was then called) Zaire in 1976 (this silver Mitsubishi Sigma has a different license plate). They couldn’t be the same physical virus anyway, because each person hosts millions and millions of virions, each cell has a varied population of viruses, and each virion has a relatively short lifespan.

There is no universal definition for the classification of viruses below the level of a species. But there are lots of terms that are used – most are listed in the heading to this section. In filovirus-land, the Study Group has sought to impart some order upon the chaos [3].

A virus strain needs to have 1 or more observable, genetically stable and unique differences compared to other viruses in the same species. For instance, one might cause a disease that is different from the one we know. So, apart from a different license plate, it might also have an Awesome Mix #1 CD in the tray.

A variant has some genetic sequence or other differences that may result in a slightly different observable change. The West African EBOV is a variant, not a strain, of Zaire ebolavirus, and was named after the Makona River (see figure), which borders all three countries that have had widespread and intense transmission.[5] For example, these from Guinea and Sierra Leone:

• Ebola virus H.sapiens-wt/GIN/2014/Makona-Kissidougou-C15, complete genome
• Ebola virus H.sapiens-wt/GIN/2014/Makona-Gueckedou-C07, complete genome
• Ebola virus H.sapiens-wt/SLE/2014/Makona-EM104

A virus isolate is a virus sample obtained by growing, or ‘culturing’, it in cells or tissues. Variants can, therefore, be represented by isolates. These isolates can be identical or slightly different (your neighbour could order the exact same car as you did, but he would still have a different licence plate and no bobbleheads or fluffy dice).

The naming schemes go into further detail, but you can read about them in [3].

The disease.

The disease caused by EBOV, SUDV, TAFV and BDBV is called Ebola disease (EVD). Frankly, that is a tough one to explain after all of the above. It reads as though we are talking about just 1 virus causing disease (EBOV). But not so. Viruses from 4 species cause EVD – EBOV, SUDV, TAFV and BDBV. Diseases are named according to the World Health Organisation’s International Classification of Diseases (ICD) site (4), and the name of this disease dates back many years. From January 2022, ICD-11 replaced ICD-10, and the new format includes specific disease groupings.

 The disease was called Ebola haemorrhagic fever, but it is not now. Ebola virus disease was used generically for a time, but now the top-level name is Ebola disease, where it is, by itself, a proper noun – that is its name – so it always gets the capital ‘E’. And, to continue with the taxonomy above, Ebola disease (EBOD) is caused by a virus that can be further classified by species. In the West Africa 2013-2016 epidemic, EVD was due to infection by an Ebola virus variant classified in the species Ortheoebolvirus zairense (formerly Zaire ebolavirus), and so it was Ebola virus disease (EVD).

Navigating a tree in the ebolavirus jungle.

Lastly, I’ve cobbled together a tree of genomes from of 5 ebolavirus species. It may help. Or not.

 

References…

1. ICTV Virus Taxonomy: 2013 Release http://www.ictvonline.org/virusTaxonomy.asp
2. Ebola virus disease World Health Organization fact sheet http://www.who.int/mediacentre/factsheets/fs103/en/
3. Virus nomenclature below the species level: a standardized nomenclature for natural variants of viruses assigned to the family Filoviridae.Arch Virol (2013) 158:301–311. http://download.springer.com/static/pdf/619/art%253A10.1007%252Fs00705-012-1454-0.pdf?auth66=1408093824_af9d701ab93574066469a6f6745c11d7&ext=.pdf
4. International Classification of Diseases (ICD) http://www.who.int/classifications/icd/en/
5. Nomenclature- and Database-Compatible Names for the Two Ebola Virus Variants that Emerged in Guinea and the Democratic Republic of the Congo in 2014 http://www.mdpi.com/1999-4915/6/11/4760
6. Replace the species name Lake Victoria marburgvirus with Marburg marburgvirus in the genus Marburgvirushttps://talk.ictvonline.org/ICTV/proposals/2010.010bV.A.v3.Ebolavirus-ren-Sp.pdf
7. Reconsidering Ebola virus nomenclature: a call for a stigma-free and precise terminology
   https://www.thelancet.com/journals/langlo/article/PIIS2214-109X%2825%2900139-1/fulltext

*IMPORTED POST

This post from 13AUG2014 was originally posted on my old blog platform, virologydownunder.blogspot.com.au, and has now been moved here and lightly updated. 

UPDATES

1. 22MAY2026. Updating the definition of Ebola virus disease to Ebola disease, with subgroups in line with ICD-11 disease classification and ICTV nomenclature