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Population Structure of Opisthorchis Felineus

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Population Structure of Opisthorchis Felineus ©2014 Institute of Parasitology, SAS, Košice DOI 10.2478/s11687-014-0246-3 HELMINTHOLOGIA, 51, 4: 309 – 317, 2014 Population structure of Opisthorchis felineus (Trematoda) and its second intermediate hosts – cyprinid fishes in the Ob-Irtysh focus of opisthorchiasis, based on allozyme data O. N. ZHIGILEVA1,*, V. V. OZHIREĽEV2, T. F. STEPANOVA2, T. I. MOISEENKO3 1Department of Ecology and Genetics, Tyumen State University, Tyumen, Russia, *E-mail: [email protected]; 2Laboratory for Environmental Monitoring of Natural Focal Infections, Tyumen Research Institute of Regional Infection Diseases, Tyumen, Russia; 3V.I. Vernadsky Institute of Geochemistry and Analytical Chemistry of RAS, Moscow, Russia, E-mail: [email protected] Summary Genetic variability of West Siberian populations of Opis- cesses, such as the restructuring of the genome during the thorchis felineus and two species of cyprinid fish, its se- passage of different stages and mitotic recombination cond intermediate hosts, was studied by isozyme analysis. (Grevelding, 1999; Bayne & Grevelding, 2003; Semyo- Low levels of allozyme variation and genetic differentia- nova et al., 2005; Be’er, 2005). tion in O. felineus from the Ob-Irtysh focus of opisthorchi- Particular attention is paid to trematodes of the family asis were detected. The proportion of polymorphic loci was Opisthorchidae, which are pathogenic for humans. Opis- 21.1 %, the average observed heterozygosity (Hobs) was thorchiasis is generally caused by O. felineus and O. viver- 0.008, and expected heterozygosity (Hexp) was 0.052. For rini trematodes in Southeast Asia, Central and Eastern most loci in O. felineus deficit of heterozygotes (FIS = Europe. It is estimated that worldwide over 23 million 0.7424) was observed. A comparison of population genetic people are infected with O. felineus and more than 16 mil- structure of fish and parasites showed they were not con- lion people with O. viverrini, with prevalence rates of 40 to gruent. Estimates of genetic differentiation of the parasite 95 percent in some areas (WHO Report, 1995; Andrews et were smaller than for the fish – its intermediate host. Mi- al., 2008). Large natural focus of opisthorchiasis exists in gration and population structure of the second intermediate the Ob-Irtysh basin in West Siberia. Prevalence of this hosts do not play an important role in formation of the infestation in the local human populations in some areas population-genetic structure of O. felineus in the Ob-Irtysh reaches 80 %. The source of infection is known to be the focus of opisthorchiasis. cyprinid fishes, from which the roach, dace, and especially ide play the leading role. At the center of natural focus Keywords: Opisthorchis felineus; cyprinid fishes; Ob- 100 % of ides infested by metacercariae of O. felineus, Irtysh river basin; genetic structure of populations; iso- with the intensity of infection exceeding 1000 larvae per zymes individual fish. Genetic variability of O. felineus was studied using the Introduction methods of sequencing the sites of nuclear and mitochon- drial genome (Katokhin et al., 2008; Shekhovtsov et al., In recent years, the population genetic studies of parasites 2009), polymerase chain reaction (Pauly et al., 2003), and have attracted much attention of researchers. This is not karyotyping (Polyakov et al., 2010). The authors found a only a practical interest, but also to a large extent the de- low level of polymorphism in the West-Siberian popula- velopment of new methods of studying the genetic struc- tions of O. felineus, although other species of this genus ture of microscopic organisms with poorly studied ge- are known to have a wide genetic variability (Sithithaworn nome. Significant progress has been made in studying the et al., 2007; Saijuntha et al., 2007; 2008a, b), influencing genetics of trematodes – parasites with complex life cycles, the epidemiological situation (Andrews et al., 2008). To and parthenogenetic reproduction of the larval stages. For study the population structure of O. viverrini microsatel- some species of trematodes the full sequencing of the mi- lites (Laoprom et al., 2010), RAPD-markers (Sithithaworn tochondrial genome (Shekhovtsov et al., 2010) and more et al., 2007) and isozyme markers (Saijuntha et al., 2006 a, than 85 % of the transcriptome (Young et al., 2010) are b) were used. Despite some difficulties in the interpretation completed. In some cases, the life cycles of trematodes of isozyme profiles of parasites (Rannala, 1991; Vilas et were a model for studying fundamental biological pro- al., 2002), isozyme analysis is a valuable method for re- 309 solving disputes of systematics and population genetics of temperature of 0 ± 4 °C. They were then viewed under a parasites (Andrews & Chilton, 1999; Šnábel et al., 2006). microscope to assess the extent of infection, identify the The study of population structure of parasites is not possi- trematodes found to a species level and determine their ble without data on genetic subdivision of their hosts. viability. Muscles containing viable larvae of O. felineus, Snails play a major role for parasitism of trematodes, but in were fed to hamsters, 10 g of tissue per animal. Three some cases, there is the effect of population structure and months later, adult flukes were recovered in the liver, migrations of the second intermediate hosts for the parasite washed several times in saline and then frozen in micro- population structure (Keeney et al., 2007). The aim of this tubes for subsequent electrophoretic study. The validity of research is a comparative study of population genetic O. felineus identification was confirmed by morphological structure of O. felineus and their intermediate hosts, the study. There were collected 192 samples (each containing cyprinid fishes, in the Ob-Irtysh focus of opisthorchiasis. 1 – 5 individuals) of adult O. felineus. Additionally we took the samples of liver tissue and the blood of hamsters Material and methods (infected and not infected) which were used as a control. Tissue samples were stored frozen at -40 °C. Proteins were Fish and O. felineus metacercariae were collected from 9 extracted in a standard way using Tris-HCl buffer (pH 8.0) rivers of the Ob-Irtysh river basin, West Siberia, Russia, as follows. The sample was homogenized with a glass rod during the period November-January 2008 – 2010 (Fig. 1). on the ice in an equal volume of buffer, frozen, thawed, The roach Rutilus rutilus lacustris Pallas, 1811 (Cypri- and kept for half an hour at -4 °C, then the homogenate niformes: Cyprinidae) was obtained from the 11 localities, was centrifuged at 3000 g per minute 30 minutes at 4 °C. the ide Leuciscus idus Linnaeus, 1758 (Cypriniformes: The supernatant was mixed with a solution for the applica- Cyprinidae) – from 16 localities. A total of 316 specimens tion of proteins on the gel (40 % sucrose solution, mixed of roach and 331 specimens of ide were surveyed with the bromophenol blue dye). (Table 1). Adult O. felineus were obtained by infection of Vertical electrophoresis in 7.5 % polyacrylamide gel the golden (Syrian) hamster Mesocricetus auratus in the (Maurer, 1971) in a continuous Tris-borate-EDTA buffer standard vivarium conditions (Loskutova, 1980). A total of system (Peacock & Dingman, 1967) was used for protein 30 hamsters were infected. We used muscles of the fish separation. Electrophoresis was performed in the following infected with metacercariae of O. felineus, which were mode: 80 mA, 10 – 12 V/cm for 2.5 hours. Histochemical collected from the same rivers (8 localities) as an invasive identification of proteins was carried out in accordance material. Muscle samples of fish, destined for infection, with the guidelines (Korochkin et al., 1977; Richardson, have been delivered to the laboratory in coolers with a 1986). Six enzymes: malic enzyme (ME, 1.1.1.40), lactate Fig. 1. Places of sample collection: 1 – SSp, 2 – SSs, 3 – SSh, 4 – Okm, 5 – Ob, 6 – Ok, 7 – On , 8 – Os, 9 – BSl, 10 – Ihm, 11 – Ik, 12 – Kb, 13 – Kk, 14 – Km, 15 – Kl, 16 – It, 17 – Tus, 18 – Tk, 19 – Ti, 20 – Tu Geographical localities codes listed in Table 1. 310 Table 1. Places of sample collection and the amount of material Places of sample collection Code Amount of material Ide Roach O. felineus Severnaja Sosva River (Village Pugory) SSp 34 31 Severnaja Sosva River (Village Sosva) SSs 34 34 20 Severnaja Sosva River (Village Khulimsunt) SSh 30 15 Ob River (Village Kazym Mys) Okm 8 21 Ob River (Village Belogorje) Ob 22 Ob River (Village Kedrovii) Ok 22 8 Ob River (Nefteyugansk) On 8 17 Ob River (Sutgut) Os 14 Bolshoj Salym River (Village Lyampino) BSl 31 32 Irtysh River (Khanty-Mansijsk) Ihm 57 Irtysh River (estuary of Konda River) Ik 18 Irtysh River (Village Bolchary) Kb 30 30 Konda River (Village Lugovoj) Kl 15 Konda River (Village Kondinskoje) Kk 30 10 Konda River (Village Mezhdurechensk) Km 31 30 15 Irtysh River (Tobolsk) It 18 20 Tura River (Village Sazonovo) Tus 10 34 Tobol River (Kurgan) Tk 12 38 Ik River (tributary of the Tobol River in Kurgan area) Ti 51 Uj River (tributary of the Tobol River in Kurgan area) Tu 9 Total 20 331 316 192 dehydrogenase (LDH, 1.1.1.27), aspartate aminotransfer- Results ase (GOT, 2.6.1.1), superoxide dismutase (SOD, 1.15.1.1), nonspecific esterase (EST, 3.1.1.n) and myogenes, were Such enzymes as LDH, ME and GOT in O. felineus appear studied both in the parasites and the hosts. on electrophoregrams in the form of an invariant band. According to the results of electrophoretic analysis the These loci are monomorphic in O. felineus, whereas in O. allele frequencies, proportion of polymorphic loci (P), viverrini they were found polymorphic (Saijuntha et al., indicators of the mean observed (Hobs) and expected hete- 2007). Myogenes presented six bands on electrophore- rozygosity (Hexp), the indices of Nei’s genetic identity grams, all of them were also monomorphic in O.
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