1. Context
2. Objectives
3. Methods
3.1. Search Protocols, Data Resources, and Registration
3.2. Selection Criteria
3.3. Quality Assessment, Study Selection, and Data Extraction
3.4. Analysis
4. Results
4.1. Study Screening
4.2. Characteristics of Included Studies
| Author and Reference | Publication Year | HDV Genotyping Method | HDV Genotype Classification | Sampling Location, No. | HDV Genotype, No (%) | Notes | |||
|---|---|---|---|---|---|---|---|---|---|
| HDV I (HDV-1) | HDV II (HDV-2 or HDV-4) | HDV III (HDV-3) | Othera | ||||||
| Wu et al. (40) | 1995 | RFLP | Old | Taiwan, 88 | 24 (27.3) | 64 (72.3) | 0 (0) | 0 (0) | |
| Casey et al. (81) | 1996 | RFLP | Old | Peru, 37 | 0 (0) | 0 (0) | 37 (100) | 0 (0) | |
| Niro et al. (45) | 1997 | Sequencing | Old | Italy, 46 | 46 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Shakil et al. (71) | 1997 | Sequencing | Old | Greece, 30 | 30 (100) | 0 (0) | 0 (0) | 0 (0) | |
| USA, 22 | 22 (100) | 0 (0) | 0 (0) | 0 (0) | |||||
| Albania, 10 | 10 (100) | 0 (0) | 0 (0) | 0 (0) | |||||
| Cotrina et al. (70) | 1998 | Sequencing | Old | Spain, 37 | 37 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Wu et al. (41) | 1998 | RFLP and sequencing | Old | Taiwan, 58 | 5 (8.6) | 53 (91.4) | 0 (0) | 0 (0) | Five samples presumed as HDV IIb |
| Ivaniushina et al. (82) | 2001 | RFLP and sequencing | Old | Russia, 29 | 14 (48.3) | 15 (51.7) | 0 (0) | 0 (0) | |
| Quintero et al. (85) | 2001 | Sequencing | Old | Venezuela, 12 | 7 (58.3) | 0 (0) | 5 (41.7) | 0 (0) | |
| Kao et al. (42) | 2002 | RFLP | Old | Taiwan, 31 | 11 (35.5) | 18 (58.1) | 0 (0) | 2 (6.4) | Two with mixed HDV I and HDV II infection |
| Watanabe et al. (79) | 2003 | Sequencing | Old | Japan, 33 | 2 (6.1) | 31 (93.9) | 0 (0) | 0 (0) | One HDV IIa and 30 HDV IIb |
| Bozdayi et al. (34) | 2004 | RFLP | Old | Turkey, 59 | 59 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Takahashi et al. (55) | 2004 | Sequencing | Old | Mongolia, 20 | 20 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Kaymakoglu et al. (35) | 2005 | RFLP | Old | Turkey, 19 | 19 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Tsatsralt-Od et al. (57) | 2005 | Sequencing | Old | Mongolia, 117 | 117 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Parana et al. (17) | 2006 | Reverse hybridization | Old | Brazil, 40 | 22 (55) | 0 (0) | 18 (45) | 0 (0) | |
| Su et al. (12) | 2006 | RFLP | New | Taiwan, 133 | 51 (39.1) | 82 (60.9) | 0 (0) | 0 (0) | 74 HDV IIa and eight HDV IIb |
| Tsatsralt-Od et al. (56) | 2006 | Sequencing | Old | Mongolia, 32 | 32 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Altuglu et al. (36) | 2007 | Sequencing | Old | Turkey, 26 | 26 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Moatter et al. (48) | 2007 | RFLP | Old | Pakistan, 23 | 23 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Gomes-Gouvea et al. (18) | 2008 | Sequencing | New | Brazil, 14 | 0 (0) | 0 (0) | 14 (100) | 0 (0) | |
| Khan et al. (83) | 2008 | Sequencing | Old | Tajikistan, 10 | 10 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Mohebbi et al. (26) | 2008 | Sequencing | New | Iran, 22 | 22 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Esmaeili et al. (27) | 2009 | Sequencing | New | Iran, 26 | 26 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Makuwa et al. (52) | 2009 | Sequencing | New | Gabon, 17 | 10 (58.8) | 0 (0) | 0 (0) | 7 (41.2) | Two HDV-7 and five HDV-8 |
| Mirshafiee et al. (28) | 2009 | RFLP | Old | Iran, 13 | 13 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Hofmann et al. (66) | 2010 | Sequencing | New | Germany, 42 | 42 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Chang et al. (43) | 2011 | Sequencing | New | Taiwan, 99 | 5 (5.1) | 94 (94.9) | 0 (0) | 0 (0) | 41 HDV-2, 51 HDV-4, and two HDV-2/HDV-4 mixed infection |
| Foupouapouognigni et al. (64) | 2011 | Sequencing | New | Cameroon, 25 | 22 (88) | 0 (0) | 0 (0) | 3 (12) | One HDV-5, one HCV-6, and one HDV-7 |
| Pollicino et al. (46) | 2011 | Sequencing | New | Italy, 21 | 21 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Le Gal et al. (37) | 2012 | Sequencing | New | Turkey, 34 | 34 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Mansour et al. (67) | 2012 | Sequencing | New | Mauritania, 28 | 25 (89.3) | 0 (0) | 0 (0) | 3 (10.7) | Three HDV-5 |
| Mansour et al. (68) | 2012 | Sequencing | New | Mauritania, 31 | 28 (90.3) | 0 (0) | 0 (0) | 3 (9.7) | Three HDV-5 |
| Perveen et al. (49) | 2012 | RFLP and sequencing | New | Pakistan, 22 | 22 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Ghamari et al. (29) | 2013 | Sequencing | New | Iran, 12 | 12 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Karaca et al. (38) | 2013 | RFLP | Old | Turkey, 32 | 32 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Popescu et al. (69) | 2013 | Sequencing | New | Romania, 40 | 40 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Sy et al. (61) | 2013 | Sequencing | New | Vietnam, 21 | 19 (90.5) | 2 (9.5) | 0 (0) | 0 (0) | Two HDV-2 |
| Andernach et al. (58) | 2014 | Sequencing | New | Nigeria, 15 | 8 (53.3) | 0 (0) | 0 (0) | 7 (46.7) | Five HDV-5, two HDV-6 |
| Braga et al. (19) | 2014 | Sequencing | New | Brazil, 28 | 0 (0) | 0 (0) | 28 (100) | 0 (0) | |
| Bulut et al. (39) | 2014 | RFLP and sequencing | Old | Turkey, 113 | 113 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Butt et al. (50) | 2014 | Sequencing | New | Pakistan, 21 | 21 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Crispim et al. (20) | 2014 | RFLP and sequencing | Old | Brazil, 38 | 0 (0) | 0 (0) | 38 (100) | 0 (0) | |
| Han et al. (80) | 2014 | Sequencing | New | Kiribati, 14 | 14 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Kay et al. (21) | 2014 | Reverse hybridization | Old | Brazil, 90 | 0 (0) | 0 (0) | 90 (100) | 0 (0) | |
| Servant-Delmas et al. (77) | 2014 | Sequencing | New | France, 14 | 12 (85.7) | 0 (0) | 0 (0) | 2 (14.3) | One HDV-6 and one HDV-7 |
| Botelho-Souza et al. (22) | 2015 | RFLP and sequencing | Old | Brazil, 52 | 4 (7.7) | 0 (0) | 48 (92.3) | 0 (0) | |
| Lin et al. (44) | 2015 | Sequencing | New | Taiwan, 153 | 13 (8.5) | 140 (91.5) | 0 (0) | 0 (0) | 54 HDV-2 and 86 HDV-4 |
| Sadeghian et al. (30) | 2015 | RFLP | Old | Iran, 12 | 10 (83.3) | 2 (16.7) | 0 (0) | 0 (0) | |
| Shirvani-Dastgerdi et al. (31) | 2015 | Sequencing | New | Iran, 34 | 34 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Yacoubi et al. (84) | 2015 | Sequencing | New | Tunisia, 11 | 11 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Borzacov et al. (23) | 2016 | Sequencing | New | Brazil, 22 | 0 (0) | 0 (0) | 22 (100) | 0 (0) | |
| Francois-Souquiere et al. (53) | 2016 | Sequencing | New | Gabon, 16 | 2 (12.5) | 0 (0) | 0 (0) | 14 (87.5) | 14 HDV-8 |
| Opaleye et al. (59) | 2016 | Sequencing | New | Nigeria, 14 | 14 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Chen et al. (74) | 2017 | Sequencing | Old | China, 48 | 0 (0) | 48 (100) | 0 (0) | 0 (0) | |
| Makiala-Mandanda, et al. (75) | 2017 | Sequencing | New | Congo, 12 | 12 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Nguyen et al. (62) | 2017 | Sequencing | New | Vietnam, 25 | 5 (20) | 20 (80) | 0 (0) | 0 (0) | |
| Aberra et al. (76) | 2018 | Sequencing | New | Ethiopia, 12 | 12 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Aftab et al. (51) | 2018 | Sequencing | New | Pakistan, 17 | 17 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Binh et al. (63) | 2018 | Sequencing | New | Vietnam, 57 | 52 (91.2) | 5 (8.8) | 0 (0) | 0 (0) | |
| Butler et al. (65) | 2018 | Sequencing | New | Cameroon, 211 | 138 (65.4) | 0 (0) | 0 (0) | 73 (34.6) | 11 HDV-6, 61 HDV-7, one HDV-8 |
| Jackson et al. (72) | 2018 | Sequencing | New | Australia, 169 | 136 (80.5) | 6 (3.5) | 0 (0) | 27 (16) | 27 HDV-5 |
| Komas et al. (73) | 2018 | Sequencing | New | Central African Republic, 18 | 18 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Meysami et al. (32) | 2018 | RFLP and sequencing | Old | Iran, 37 | 32 (86.5) | 3 (8.1) | 0 (0) | 2 (5.4) | Two indeterminate isolates; sequencing of one indeterminate and one HDV II isolate resulted in HDV-1 genotypes. |
| Ricco et al. (47) | 2018 | Sequencing | New | Italy, 69 | 69 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Romania, 53 | 53 (100) | 0 (0) | 0 (0) | 0 (0) | |||||
| Shirazi et al. (78) | 2018 | Sequencing | New | Israel, 55 | 55 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Da Silva et al. (24) | 2019 | Sequencing | New | Brazil, 54 | 4 (7.4) | 0 (0) | 48 (88.9) | 2 (3.7) | Two HDV-5 |
| Groc et al. (54) | 2019 | Sequencing | New | Gabon, 42 | 23 (54.8) | 0 (0) | 0 (0) | 19 (45.2) | Seven HDV-7 and 12 HDV-8 |
| Ifeorah et al. (60) | 2019 | Sequencing | New | Nigeria, 10 | 9 (90) | 0 (0) | 0 (0) | 1 (10) | One HDV-6 |
| Karimzadeh et al. (33) | 2019 | Sequencing | New | Germany, 72 | 72 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Italy, 18 | 18 (100) | 0 (0) | 0 (0) | 0 (0) | |||||
| Spain, 12 | 12 (100) | 0 (0) | 0 (0) | 0 (0) | |||||
| Iran, 14 | 14 (100) | 0 (0) | 0 (0) | 0 (0) | |||||
| Scarponi et al. (25) | 2019 | Sequencing | New | Brazil, 26 | 26 (100) | 0 (0) | 0 (0) | 0 (0) | |
| Spaan et al. (11) | 2020 | Sequencing | New | UK, 39 | 18 (46.2) | 0 (0) | 0 (0) | 21 (53.8) | 21 HDV-5 |
aHDV-5, HDV-6, HDV-7, HDV-8, mixed infection, and unknown genotypes.
4.3. Country-Level, Regional, and Global Distribution of HDV Genotypes
| Region, Country | Records (N) | Isolates (N) | HDV Genotypesa | |||
|---|---|---|---|---|---|---|
| HDV I (HDV-1) | HDV II (HDV-2 or HDV-4) | HDV III (HDV-3) | Others (HDV-5, -6, -7, or -8) | |||
| Africa | ||||||
| Cameroon | 2 | 236 | High | Very low | Very low | Intermediate |
| The Central African Republic | 1 | 18 | Very high | Very low | Very low | Very low |
| Congo | 1 | 12 | Very high | Very low | Very low | Very low |
| Ethiopia | 1 | 12 | Very high | Very low | Very low | Very low |
| Gabon | 3 | 75 | Intermediate | Very low | Very low | High |
| Mauritania | 2 | 59 | High | Very low | Very low | Low |
| Nigeria | 3 | 39 | High | Very low | Very low | Intermediate |
| Tunisia | 1 | 11 | Very high | Very low | Very low | Very low |
| Total | 14 | 462 | High | Very low | Very low | Intermediate |
| Asia | ||||||
| China | 1 | 48 | Very low | Very high | Very low | Very low |
| Japan | 1 | 33 | Low | High | Very low | Very low |
| Mongolia | 3 | 169 | Very high | Very low | Very low | Very low |
| Pakistan | 4 | 83 | Very high | Very low | Very low | Very low |
| Taiwan | 6 | 560 | Intermediate | High | Very low | Very low |
| Tajikistan | 1 | 10 | Very high | Very low | Very low | Very low |
| Vietnam | 3 | 103 | High | Intermediate | Very low | Very low |
| Total | 19 | 1006 | Intermediate | High | Very low | Very low |
| Europe | ||||||
| Albania | 1 | 10 | Very high | Very low | Very low | Very low |
| France | 1 | 14 | High | Very low | Very low | Low |
| Germany | 2 | 114 | Very high | Very low | Very low | Very low |
| Greece | 1 | 30 | Very high | Very low | Very low | Very low |
| Italy | 4 | 154 | Very high | Very low | Very low | Very low |
| Romania | 2 | 93 | Very high | Very low | Very low | Very low |
| Russia | 1 | 29 | Intermediate | High | Very low | Very low |
| Spain | 2 | 49 | Very high | Very low | Very low | Very low |
| UK | 1 | 39 | Intermediate | Very low | Very low | High |
| Total | 15 | 532 | High | Low | Very low | Low |
| Middle East | ||||||
| Iran | 8 | 168 | High | Low | Very low | Very low |
| Israel | 1 | 55 | Very high | Very low | Very low | Very low |
| Turkey | 6 | 283 | Very high | Very low | Very low | Very low |
| Total | 15 | 506 | Very high | Low | Very low | Very low |
| North America | ||||||
| US | 1 | 22 | Very high | Very low | Very low | Very low |
| Total | 1 | 22 | Very high | Very low | Very low | Very low |
| Oceania | ||||||
| Australia | 1 | 169 | High | Low | Very low | Intermediate |
| Kiribati | 1 | 14 | Very high | Very low | Very low | Very low |
| Total | 2 | 183 | High | Low | Very low | Low |
| South America | ||||||
| Brazil | 9 | 364 | Intermediate | Very low | High | Very low |
| Peru | 1 | 37 | Very low | Very low | Very high | Very low |
| Venezuela | 1 | 12 | High | Very low | Intermediate | Very low |
| Total | 11 | 413 | Intermediate | Very low | High | Very low |
| World (Total) | 77 | 3124 | High | Intermediate | Low | Low |
aPrevalence of HDV genotypes: < 1%, very low; 1 - 14.9%, low; 15 - 49.9%, intermediate; 50 - 98.9%, high; ≥ 99%, very high.

