—209— The Korean Journal of Parasitology Vol. 39, No. 3, 209-221, September 2001 Mini-Review Trematodes of the family Opisthorchiidae: a minireview Sandie KING1),2) and Tomá˘s SCHOLZ1)* Institute of Parasitology1), Academy of Sciences of the Czech Republic, Brani˘sovská 31, 37005 Ceské˘ Bud˘ejovice, Czech Republic, and Institute of Biomedical and Life Sciences2), University of Glasgow, Glasgow, Scotland, UK, G12 8QQ Abstract: Examination of the original descriptions of genera placed within the family Opisthorchiidae has revealed that only 33 of the original 43 genera are valid members of this family. Further study of these descriptions should also reveal that many of the subfamilies are also invalid. With reference to the original descriptions of these genera, and subsequent literature, a brief survey of the family has been compiled. Information on the spectrum of definitive hosts that these helminths parasitize is provided, as well as information on the life cycles, geographic distribution, and socioeconomic impacts of the family. More in-depth information is given on those species that are of particular medical importance; namely, Clonorchis sinensis, Opisthorchis viverrini, and O. felineus. The final aims of this review are to provide information on the entire genera of the family Opisthorchiidae, which will aid understanding of the phylogenetic relationships not only within the family, but also within the Class Trematoda. Key words: Opisthorchiidae, liver flukes, classification, survey of genera, host spectrum, distribution humans (Yamaguti, 1971). INTRODUCTION The family Opisthorchiidae has been studied fairly exhaustively in a number of monographs The liver flukes (Digenea) of the genera or comprehensive volumes: Skrjabin and Clonorchis Looss, 1907 and Opisthorchis Petrov (1950), Yamaguti (1958, 1971, and Blanchard, 1895 are notorious as causative 1975). In these works, the family was thought agents of human infections transmitted by to include approximately 50 genera, fish. The disease clonorchiasis, and the closely encompassing several hundred species; related opisthorchiasis, annually infect however, the lack of more recent research has millions of people in regions where raw or brought the taxonomic status and validity of undercooked fish harbouring opisthorchiid these genera into question. Also, as no new metacercariae are consumed, particularly in data have been compiled recently as a specific Southeast Asia and circumpolar parts of condensed volume, very little is known about Eurasia and North America. However, the the family as a whole. The species compos- family Opisthorchiidae also includes numer- ition, geographical distribution, life cycles and ous genera whose members rarely infect phylogenetic relationships within the family have all been insufficiently examined. It is the purpose of this review, therefore, to ·Received 14 August 2001, accepted after give a brief summary of the family as a whole revision 27 August 2001. and to provide information concerning the *Corresponding author (e-mail: tscholz@paru. cas.cz) taxonomy of the family in an attempt to —210— eliminate invalidities and synonyms amongst fication used by Brooks et al. (1985) are not genera. Information will also be provided on reliable enough to base the phylogenetics of the host spectrum, life cycles, geographic the digeaneans on. After his analysis of the distribution, and socioeconomic factors of the characters used by Brooks et al. (1985), he family. states that 97 of the 212 characters used in the cladistic classification of the Digenea were CLASSIFICATION AND TAXONOMY invalidly used, resulting in the homoplasy increasing by 18% to 37%, with an accom- The main problem with classifying any panying decrease in resolution from 82% to group of digenetic trematodes is the fact that 32%. they have complex life cycles involving 2-4 Cribb et al. (2001) have attempted to further hosts and many different larval stages. Thus, unravel some of the mysteries surrounding there are many morphologically different forms digenean evolution and expand on such on which taxonomy can be based. studies of Brooks et al. (1985) and Pearson Yamaguti (1971) refers to his previous clas- (1992), among others, in order to resolve some sifications and, indeed, those of others, when of the many inconsistencies that can be found he maintains that the adult morphology of in this area of study. They have attempted to digeneans is the best method of classification. do this by combining many data sets, However, he also states: “We must be content including those containing morphological and for the present with an artificial classification molecular characters, to provide a truer based chiefly on adult morphology.” It is with representation of the relationships between this statement in mind that another school of digenean families. The use of combined data thought has arisen, which many believe is a sets can be controversial in itself, as outlined much more accurate means of classification. It by de Queiroz et al. (1995) who have reviewed involves the examination of cercariae, as these the arguments both for and against the use of are believed to be recapitulations of ancestral combined data sets in phylogenetic analyses. forms, and thus enable the production of a Although the studies mentioned above have more phylogenetically accurate classification. used extensive phylogenetic analysis in order It is considered that the use of cercarial forms to try and resolve the relationships between all also eliminates the possibility of misidenti- the families within the Digenea, such work is fication through convergent evolution (Brooks important when individual families are re- et al. 1985). examined in order to validate subfamilies and Brooks et al. (1985) went some way towards genera. In essence, when classifying addressing the issues concerned with the trematodes within a particular family, in this classification of digeneans and have carried case the Opisthorchiidae, it is the species that out an extensive study on the phylogenetic are closely related enough to be included relationships of the entire Digenea. Using both within the same family, subfamily, and genus adult morphology and larval forms, they have that are being identified. The taxonomic state attempted to provide a starting point for future of the entire class or subclass being studied phylogenetic studies on this diverse group, plays an important role in such a re- which, they hope, will grow into a compre- examination as closely related families can hensive and increasingly accurate method of provide information on the composition of the classification. However, the use of evidence family of interest. from both adult and cercarial forms seems to Perhaps still considered as the most further outline the prevalence of conflicting extensive attempt to form a complete theories concerning the classification of this classification of digenetic trematodes was that group. Until such inconsistencies can be of Yamaguti (1971) (with the life cycles treated overcome to a greater extent, the Digenea and separately in 1975). Although three decades methods used to classify them seem destined old, the material in these volumes is still to remain under scrutiny. Indeed, Pearson referred to as one of the most comprehensive (1992) argues that the methods of classi- studies of digeneans, and for this review, these —211— volumes were a starting point from which to The two genera found not to belong to the source the original descriptions of members of Opisthorchiidae are thought to be synonymous the Opisthorchiidae. Subsequently, it was with one another, and, as indicated by their these original descriptions which formed the morphology, belong to the family Acantho- basis of the reclassification reported in this stomidae (subfamily Acanthostominae of the study. Cryptogominidae according to some authors) Firstly, by referring to papers containing the as originally reported. Thus, with all of the original descriptions of each genus, 11 genera above genera omitted from the family, it is can be omitted from the family on the basis of proposed that the family Opisthorchiidae being invalid or not belonging to the contain only 33 genera, as listed below: Opisthorchiidae at all: Valid genera of Opisthorchiidae Invalid genera Agrawalotrema Sahay & Sahay, 1988 Allometorchis Baer, 1943 Allogomtiotrema Yamaguti, 1958 Synonym of Metametorchis Morozov, 1939 — Amphimerus Barker, 1911 see Skrjabin & Petrov (1950) Cladocystis Poche, 1926 Assamia Gupta, 1955 Clonorchis Looss, 1907 Preoccupied by Assamia Sorensen, 1884 Cyclorchis Luhe, 1908 (Arachnida) and Assamia Buckton, 1896 Delphinicola Yamaguti, 1933 (Insecta) — Lakshminarayana & Hafeezullah Diasiella Travassos, 1949 (1974) Erschoviorchis Skrjabin, 1945 Satyapalia nom. nov. proposed by Euamphimerus Yamaguti, 1941 Lakshminarayana & Hafeezullah (1974) Evranorchis Skrjabin, 1944 Brachymetra Stossich, 1904 Gomtia Thapar, 1930 Preoccupied by Brachymetra Mayr, 1865 Hepatiarius Fedzullaev, 1961 (Insecta) — Poche (1926) Holometra Looss, 1899 Synonym of Ratzia Poche, 1926 Metametorchis Morozov, 1939 Diasia Travassos, 1922 Metorchis Looss, 1899 Preoccupied by Diasia Travassos, 1923 — Microtrema Kobayashi, 1915 Yamaguti (1958) Nigerina Baugh, 1958 Synonym of Diasiella Travassos, 1949 Oesophagicola Yamaguti, 1933 Gomtiotrema Gupta, 1955 Opisthorchis Blanchard, 1895 Preoccupied (Yamaguti 1958, 1971) Pachytrema Looss, 1907 Allogomtiotrema nom. nov. Proposed by Parametorchis Skrjabin, 1913 Yamaguti (1958)