Evidence of a species complex within the food-borne trematode Opisthorchis viverrini and possible co-evolution with their first intermediate hosts

Abstract

The food-borne trematodes, Opisthorchis viverrini, O. felineus and Clonorchis sinensis, have long been recognized as the cause of major human health problems, with an estimated 40 million infected persons. Of the three species of liver fluke, only O. viverrini is classified as a type 1 carcinogen because of its role as an initiator of chronic inflammation and the subsequent development of cholangiocarcinoma. At present, there are no techniques for the early diagnosis of cholangiocarcinoma and it is fatal for most patients. There is considerable variation in parasite prevalence and disease presentation in different geographical areas, the latter of which may be associated with genetic differences among parasites. In the present study, multilocus enzyme electrophoresis was used to provide a comprehensive genetic characterization of O. viverrini from different geographical localities in Thailand and the Peoples’ Democratic Republic of Laos. Parasites from different localities were compared genetically at 32 enzyme loci. The results of the genetic analyses are sufficient to reject the null hypothesis that O. viverrini represents a single species. Therefore, O. viverrini consists of at least two genetically distinct, yet morphologically similar (i.e. cryptic) species. Moreover, there was also separation of the different populations of snails (i.e. the first intermediate hosts) into two distinct genetic groups that corresponded with the delineation of O. viverrini into two species. This suggests that there may be a history of co-evolution in this host–parasite lineage. Additionally, five distinct genetic groups of parasites were detected, each of which occurred within a different and independent river wetland system. Our findings have major implications for the implementation of effective control and surveillance programs targeted to these medically important food-borne parasites.

Seasonal Transmission of Opisthorchis viverrini sensu lato and a Lecithodendriid Trematode Species in Bithynia siamensis goniomphalos Snails in Northeast Thailand

“…The snail collections were performed monthly in the same rice paddy field with an area of 1,534 m 2 in Phang Khon district, Sakon Nakhon Province, northeast Thailand, which is a known endemic area of O. viverrini s.l. 2 In addition to rain water, the area is irrigated with water from the Nam Un Dam through a network of irrigation canals. Consequently, irrigated water is available particularly in the dry season, allowing the planting two crops of rice per year.…”

“…1 Evidence from various sources indicates that O. viverrini represents a species complex. 2,3 Human infection with O. viverrini s.l. is contracted by the consumption of raw or partially cooked fish, and chronic infection leads to hepatobiliary diseases and potentially to bile duct cancer (cholangiocarcinoma [CCA]).…”

Analysis of the population genetics of Opisthorchis viverrini sensu lato in the Nam Ngum River wetland, Lao PDR, by multilocus enzyme electrophoresis

“…In northeast Thailand, O. viverrini is a major medical problem with prevalences commonly reaching 30 -80% or more in rural populations (Saowakontha et al 1993;Sripa et al 2011;. A similarly high prevalence (60.7 -86.2%) of O. viverrini infection also occurs in Lao PDR (Kobayashi et al 2000;Sayasone et al 2009) Multilocus enzyme electrophoresis (MEE) analyses by Saijuntha et al (2007) and Kiatsopit et al (2011) found that O. viverrini is a species complex, potentially consisting of genetically very distinct but morphologically similar (hence cryptic) species which are associated with specific wetlands in Thailand and Lao PDR. Additionally, independent biological evidence has revealed significant differences in body size, fecundity and infectivity of O. viverrini that occur in different wetlands, namely the Chi and Songkram in Thailand and the Nam Ngum in Lao PDR.…”

“…From this biological evidence, in conjunction with molecular genetic data, Laoprom et al (2009) suggested that O. viverrini from the Songkram wetland (Sakon Nakhon and Nakhon Phanom) is a morphologically, genetically, and biologically distinct species. Furthermore, Saijuntha et al (2007) and Kiatsopit et al (2013) have shown that the first intermediate snail host, Bithynia siamensis goniomphalos also represents a species complex consisting of cryptic species that occur in the same wetlands as the cryptic species of O. viverrini in Thailand and Lao PDR.…”

Low Genetic Diversity in Wide-Spread Eurasian Liver Fluke Opisthorchis felineus Suggests Special Demographic History of This Trematode Species

“…In contrast, when multilocus enzyme electrophoresis was used to analyze genetic variation of O. viverrini from different geographical areas in Thailand and Lao PDR, high diversity between the isolates from different localities was observed. Thus, the authors speculated that O. viverrini did not represent a single species but rather comprised two cryptic species [54]. Unfortunately, no extensive research on the population genetics of C. sinensis has been published to date.…”