Snail-borne zoonotic trematodes in edible viviparid snails obtained from wet markets in Northern Thailand

Abstract

Edible viviparid snails are suspected to be the source of human echinostomiasis in Thailand, but little is known about the prevalence of viviparid snail parasitization by echinostomes in snails sold for human consumption in wet markets. Here, the prevalence of echinostome metacercariae and the association between parasitic intensity and host size, as well as the relationship to host species, were investigated. In total, 1100 viviparid snails belonging to four species (Cipangopaludina annandalei, Filopaludina martensi martensi, F. sumatrensis polygramma and F. doliaris) were obtained from wet markets in Chiang Rai Province, Northern Thailand. All snail species were found to be infected with echinostome metacercariae with total prevalence and mean intensity values of 16.5% and 16.4, respectively. The metacercariae of the avian trematode, Thapariella anastomusa were found in Filopaludina spp. snails. Interestingly, C. annandalei identified in this study had not previously been considered a food source and this is the first report of echinostome metacercaria in this snail species. Results confirmed the role of C. annandalei as the second intermediate host of the trematode; however, the species identity of these echinostomes remains unclear. Comparative morphology of these metacercariae and their adult stage require further study, and molecular markers are necessary to confirm their identification. Prevalence and intensity of echinostomes metacercariae was significantly associated with snail species.

High diversity of trematode metacercariae that parasitize freshwater gastropods in Bangkok, Thailand, and their infective situations, morphologies and phylogenetic relationships

“…Of all seven metacercariae currently observed, only two of them, echinostome A and thapriellid, have usually been reported for their infections in freshwater snail faunas from several areas of Thailand (Anucherngchai and Chontananarth, 2016; Chantima et al ., 2018; Phalee et al ., 2018; Wiroonpan and Purivirojkul, 2018; Chantima and Rika, 2020), representing that a quite high diversity of metacercariae could be established for our study. The remaining five groups (echinostome B, echinostome C, echinostome D, Opisthorchiata-like and renicolid) still had no reports of their infections in snail hosts and can be addressed as the new records in Thailand; this finding provides an additional range of larval trematode diversity and indicates an important role and involvement of freshwater snails in trematode transmissions in ecosystems.…”

“…Regarding the investigated infected snails, all of them belonged to 14 species/subspecies and represented a high number of infected snail taxa when compared with previous studies that reported metacercarial infections in freshwater snails from Thailand (Chantima et al ., 2013, 2018; Noikong and Wongsawad, 2014; Wongsawad et al ., 2017; Chomchoei et al ., 2018; Phalee et al ., 2018; Wiroonpan and Purivirojkul, 2018; Bunchom et al ., 2020; Butboonchoo et al ., 2020; Chantima and Rika, 2020; Wiroonpan and Purivirojkul, 2021). Of the 14, the nine following taxa have never been known to be infected by metacercarial trematodes from those previous reports and can be addressed as the new host record of the metacercarial infections in Thailand: Austropeplea viridis , Filopaludina sumatrensis speciosa , Gyraulus siamensis , Indoplanorbis exustus , Physella acuta , Pomacea canaliculata , Radix auricularia , Sulcospira housei and Tarebia granifera ; this finding expanded an infective database in terms of the snail host spectrum and indicated an important role and involvement of the snail faunas in trematode transmissions among host organisms in ecosystems.…”

“…In Thailand, diversity of trematode metacercariae is relatively low for their infections in freshwater snail hosts; two groups of metacercariae, including echinostomes and thapariellids, have usually been reported from several areas (Anucherngchai and Chontananarth, 2016; Chantima et al ., 2018; Phalee et al ., 2018; Wiroonpan and Purivirojkul, 2018, 2021; Chantima and Rika, 2020). Research studies mentioning a group of echinostome metacercariae has mostly exhibited their occurrence and infection rate and categorized them depending on morphology, causing inability to clearly identify their species.…”

“…According to two gastropod groups stated above, Esch and Fernandez (1994) suggested that their biological variations in terms of reproductive biology, growth patterns and life span might contribute to their disparities in trematode community. In Thailand, more than 10 species/subspecies of freshwater snails have been reported to display their metacercarial infections, from several areas, particularly northern and northeastern parts; most of them frequently belong to prosobranch snails, including Anentome helena , Bithynia siamensis siamensis , Filopaludina doliaris , Filopaludina martensi martensi and Filopaludina sumatrensis polygramma (Chantima et al ., 2013, 2018; Noikong and Wongsawad, 2014; Wongsawad et al ., 2017; Chomchoei et al ., 2018; Phalee et al ., 2018; Wiroonpan and Purivirojkul, 2018; Bunchom et al ., 2020; Butboonchoo et al ., 2020; Chantima and Rika, 2020; Wiroonpan and Purivirojkul, 2021).…”

“…For thapariellids, it has been quite rare for genetic investigations of this metacercarial group to be considered. Likewise, most of them have often been mentioned in terms of appearance and infection rate (Anucherngchai and Chontananarth, 2016; Chantima et al ., 2018; Phalee et al ., 2018; Chantima and Rika, 2020). Species identification of thapariellid metacercariae appears to be uncomplicated because of availability of their reproductive organs, for which the number, position and arrangement of these organs could facilitate assessing the species of many trematodes.…”