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Table 1A

Recommended terms for the genetics and epidemiology of Echinococcus species.

Word/expression Definition Arguments for acceptance, references, linguistic clarifications Comments
Echinococcus Rudolphi, 1801 (Cestoda: Taeniidae) Genus in the family Taeniidae Ludwig, 1886, order Cyclophyllidea, class Cestoda, phylum Platyhelminthes, kingdom Animalia. International nomenclature; name of the genus Echinococcus [67]; must be written in italics with first letter in capital letter; abbreviation “E.” (italics followed by a dot) when in a binomen (i.e. a generic name and a specific name) or in a trinomen (a generic name, a specific name and a subspecific name – this is rare). The genus name Alveococcus (for the species Alveococcus multilocularis (Leuckart, 1863) Abuladze, 1959) was erected to separate E. multilocularis from the other species. There is no longer a taxonomic basis for such a separation, but the name is still used occasionally, particularly in Russian literature. See also Table 2A.
Echinococcus sp. One species within the genus Echinococcus. The abbreviation “sp.” (not italics) stands for a species, the identity of which is not known (e.g. in case of an undetermined Echinococcus isolate)
Echinococcus spp. More than one (or all) species within the genus Echinococcus. The abbreviation “spp.” does not indicate a species with the taxonomic definition of “species”, but stands for “species pluralis” (the Latin for “multiple species”), hence the roman letters (not italics).
spp is followed by a dot (because it is the abbreviation of a Latin expression; see e.g., i.e., as examples), thus: “spp.”
Echinococcus canadensis (Webster & Cameron, 1961) A species within the E. granulosus sensu lato species cluster. E. canadensis (Webster & Cameron, 1961) [80] corresponds to the previous “G6/G7”, “G8” and “G10” genotypes, identified by DNA sequencing [52] (see GenBank: https://www.ncbi.nlm.nih.gov/genbank/); E. canadensis belongs to E. granulosus s.l. E. canadensis cycle may involve camels and goats (G6 genotype), pigs (G7) and cervids (G8 and G10) as intermediate hosts and dogs (as well as wolves for G8 and G10) as definitive hosts; however, sheep, cattle and other ungulates may also be infected by E. canadensis, which is the second species within E. granulosus s.l., after E. granulosus s.s., to infect humans.
Genotypes may be used to differentiate between distinct molecular sequences, within the defined species; the word “strain” should no longer be used. G6 and G7 may in future be separated from this species, so at present the expression “E. canadensis cluster” is recommended.
Echinococcus equinus (Williams & Sweatman, 1963) A species within the E. granulosus sensu lato species cluster. E. equinus (Williams & Sweatman, 1963) [84] corresponds to the previous “G4” genotypes, identified by DNA sequencing [52] (see GenBank: https://www.ncbi.nlm.nih.gov/genbank/). E. equinus belongs to E. granulosus s.l.[66] E. equinus cycle usually involves members of the horse family as intermediate hosts and dogs as definitive hosts. It is also known from a wildlife cycle involving lions and zebras [9, 78].
It is associated with disease in non-human primates (lemurs) [9, 12].
However, the zoonotic potential of E. equinus infection (i.e. infection in humans) has not yet been convincingly demonstrated [2].
Echinococcus felidis Ortlepp, 1937 A species within the E. granulosus sensu lato species cluster. E. felidis Ortlepp, 1937 [59], was first described as such in 1937 by Ortlepp from the lion, Panthera leo, in South Africa; it is now recognized as a distinct species, identified by DNA sequencing [52] (see GenBank: https://www.ncbi.nlm.nih.gov/genbank/collab/); E. felidis belongs to E. granulosus s.l. [26] E. felidis cycle involves lions as definitive hosts, and it is only known from warthogs and hippos as intermediate hosts; E. felidis infection has not been recognized to be associated with disease in humans up to now [25].
Echinococcus granulosus (Batsch, 1786) sensu lato The concept of E. granulosus as one species cluster that contains all agents of cystic echinococcosis. sensu lato” and “sensu stricto” are used, when a species name (here: E. granulosus (Batsch, 1786)) [7] is used in different concepts: in a wider sense (s.l.) that includes e.g. cryptic species, or in a more restricted concept (s.s.) [52]. granulosus” should be followed by “sensu lato” whenever the precise species has not been determined.
sensu lato” should be in italics (although this is debated), without capital letters as first letters. The abbreviation of each word in “sensu lato” is followed by a dot (because it is the abbreviation of Latin words; see e.g., i.e., as examples), thus: “s.l. For publications on the clinical aspects of echinococcosis, as the clinical descriptions of the disease “cystic echinococcosis”(CE) fits with all those species within E. granulosus sensu lato that are responsible for disease in humans, the use of E. granulosus sensu lato is allowed when there was no identification of the real species.
For publications on basic research and epidemiology, molecular identification of the real species is necessary; it should be performed and indicated in the Materials and Methods section.
Echinococcus granulosus (Batsch, 1786) sensu stricto A species within the E. granulosus sensu lato species cluster. sensu stricto” and “sensu lato” are used, when a species name (here: E. granulosus (Batsch, 1786)) [7] is used in different concepts: in a wider sense (s.l.) that includes e.g. cryptic species, or in a more restricted concept (s.s.) [52, 66]. E. granulosus sensu stricto corresponds to the previous “G1”, “G2”, a microvariant of “G3”, and “G3” genotypes, identified by DNA sequencing (see GenBank: https://www.ncbi.nlm.nih.gov/genbank/); its cycle usually involves sheep as intermediate hosts and dogs as definitive hosts; cattle and other ungulates may also be infected by E. granulosus sensu stricto
sensu stricto”, which is the equivalent of a species, should be in italics (although this is debated), without capital letters as first letters. The abbreviation of each word in “sensu stricto” is followed by a dot (because it is the abbreviations of Latin words; see e.g., i.e., as examples), thus: “s.s.E. granulosus s.s. belongs to E. granulosus s.l. [66] A strongly diverging genotype from Africa (“G Omo”) is provisionally retained in E. granulosus s.s., but will have to be reclassified in the future [79].
Echinococcus multilocularis (Leuckart, 1863) A species in the genus Echinococcus. E. multilocularis (Leuckart, 1863) [50], is the agent of the disease “alveolar echinococcosis” (AE) in humans [35, 52] E. multilocularis was clearly distinguished from E. granulosus sensu lato in the middle of the 20th century [18, 77]. It involves a variety of rodents and lagomorphs as intermediate hosts depending on the geographical area, humans as accidental intermediate hosts, and various species of foxes, dog and wolf as definitive hosts. The disease caused by E. multilocularis, characterized by lesions composed of an aggregate of microcysts embedded in a granulomatous host’s reaction, is distinct from that caused by E. granulosus s.l. as well as those caused by E. vogeli and E. oligarthra.
Since then, no major genetic polymorphism has been found within E. multilocularis that would distinguish new species or even strains. For phylogeographic studies (variability at a continental scale), genetic polymorphism within the micro-satellite EmSB may be used [42].
Echinococcus oligarthra (Diesing, 1863) A species in the genus Echinococcus. E. oligarthra (Diesing, 1863) [14] is a species found in South, Central and North America (Mexico) [52, 58]. E. oligarthra cycle usually involves agouti (Dasyprocta spp.) and occasionally paca (Cuniculus paca), spiny rats (Proechimys spp.), rabbits (Sylvilagus floridanus), and opossums (Didelphis marsupialis) as intermediate hosts and various wild cat species as definitive hosts [65].
The component “arthra”, originally proposed by Diesing, comes from the ancient Greek ἄρθρα –arthra (joints) which is the plural of ἄρθρον -arthron (joint). The name is therefore not an adjective, but a noun in apposition, which does not change its ending according to the gender of the generic name. This was recognized earlier but subsequently ignored. It is responsible for a disease in humans distinct from cystic and alveolar echinococcosis, sometimes wrongly called “polycystic echinococcosis” (since it usually presents as a single cyst) [35].
“Neotropical echinococcosis” is the expression recommended to qualify human infection due either to E. vogeli or to E. oligarthra. See also Table 1C
E. ortleppi Lopez-Neyra & Soler Planas, 1943 A species within the E. granulosus sensu lato species cluster. E. ortleppi Lopez-Neyra & Soler Planas, 1943 [51] corresponds to the previous “G5” genotypes, identified by DNA sequencing [1, 52, 66] (see GenBank) E. ortleppi cycle usually involves cattle as intermediate hosts and dogs as definitive hosts; other ungulates may also be infected by E. ortleppi [24]. Human cases are known, but rare [13, 24].
E. shiquicus Xiao, Qiu, Nakao, Li, Yang, Chen, Schantz, Craig & Ito, 2005 A species in the genus Echinococcus. E. shiquicus Xiao et al., 2005 [85] is a species phylogenetically close to E. multilocularis [52] which was identified in the county of Sêrxü (in Tibetan, 石渠县 in Mandarin Chinese (pinyin: Shíqú Xiàn)) in Sichuan province, Qinghai-Tibet plateau region of Western PR China E. shiquicus (pronunciation “seshüicus”) infection has not been recognized to be associated with disease in humans up to now [35].
E. vogeli Rausch & Bernstein, 1972 A species in the genus Echinococcus. E. vogeli Rausch & Bernstein, 1972 [62] is an Echinococcus species found only in South and Central America. E. vogeli natural cycle mainly involves paca (Cuniculus paca) as intermediate hosts; it has also been documented in other rodents such as agouti (Dasyprocta spp.), and the bush dog (Speothos venaticus) and domestic dogs as definitive hosts [65]; E. vogeli is responsible for a disease in humans distinct from cystic and alveolar echinococcosis, often called “polycystic echinococcosis”, because of the presentation of the disease [35].
“Neotropical echinococcosis” is the expression recommended to qualify the human infection due either to E. vogeli or to E. oligarthra: see also Table 1C.
G genotypes Genotypes identified within the species E. granulosus s.l., previously identified as “strains”. Genotypes may be used to differentiate between distinct molecular sequences, within the defined species or complexes; the word “strain” should no longer be used when genetic characterization has been performed [52, 55]. Further definition of new species is still possible. Waiting for such definitions, G genotypes should be kept, in addition to the current species name, if necessary.
G1 and G3 genotypes Genotypes individualized within E. granulosus sensu stricto. The word “genotype” should be used; it is more appropriate than “strain” since it is based on genotyping and not on other techniques (especially morphological) previously used to distinguish between strains [52, 55]. Keeping the distinction between genotypes may be necessary for phylogeographic studies and in some circumstances for echinococcosis control (targeting animal hosts and specific cycles) [38, 41]. Best target for identification of G1 and G3 seems to be the nad5 gene region [39]. G1 is the most common genotype in sheep; G2 was first described as “Tasmanian sheep strain” but is actually cosmopolitan; G3 was initially identified from water buffalo, but is now also known from other intermediate hosts.G2 is considered a microvariant of G3 [40].
G6/G7 G8 G10 Genotypes individualized within E. canadensis (Webster & Cameron, 1961). Pending further distinction between accepted species, genotypes within E. canadensis should be qualified by the previously accepted “G” numbers G6/G7, G8 and G10 [49, 66]. G9 is no longer recognized as a distinct genotype; it is probably a microvariant of G7; the genotypic cluster G6/7 is the second most important agent of human CE worldwide; further distinction between species within the E. canadensis cluster has been proposed, but has not been accepted yet [48, 53, 54, 57].
Genotypes may be used to differentiate between distinct molecular sequences, within the defined species; the word “strain” should no longer be used.

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