The occurrence of 37-collar spined echinostome metacercariae in freshwater snails was investigated in 6 districts of Chiang Mai Province, Thailand, from October 2011 to April 2012. A total of 2,914 snails that belong to 12 species were examined, and 7 snail species (Clea helena, Eyriesia eyriesi, Bithynia funiculata, Bithynia siamensis siamensis, Filopaludina doliaris, Filopaludina sumatrensis polygramma, and Filopaludina martensi martensi) were found infected with echinostome metacercariae. The prevalence of metacercariae was the highest in Filopaludina spp. (38.5-58.7%) followed by B. funiculata (44.0%), E. eyriesi (12.5%), B. siamensis siamensis (8.2%), and C. helena (5.1%). Metacercariae were experimentally fed to hamsters and domestic chicks, and adult flukes were recovered from both hosts at days 15 and 20 post-infection. The adult flukes were identified based on morphological features, morphometrics, host-parasite relationships, and geographical distribution. They were compatible to Echinostoma revolutum or Echinostoma jurini, with only minor differences. As the adults were recovered from both hamsters and chicks, our specimens were more compatible to E. revolutum rather than E. jurini (reported only from mammals). This is the first report for metacercariae of E. revolutum in the snail host, C. helena, and also confirmed that Filopaludina spp., E. eryresi, and Bithynia spp. act as the second intermediate hosts of E. revolutum under natural conditions, which are indigenously distributed in Chiang Mai province.

The aim of this study was to conduct a freshwater snail survey in Mae Lao agricultural basin to assess the diversity with a focus on habitat types and their larval trematode infections. Snails were collected and examined in 14 sites of Mae Lao agricultural basin from August 2016 to October 2017. A total of 1,688 snail individuals were collected and classified into 7 families, 8 genera, and 12 species. Snail diversity and habitat types were higher in rice paddies than irrigation canals and streams. The most abundant species was Bithynia siamensis siamensis, representing 54.6% of the sample. Three species of snails act as first intermediate host were found with cercarial infections. They were Filopaludina sumatrensis polygramma, B. s. siamensis, and Melanoides tuberculata. The cercariae were categorized into 7 types; echinostome, monostome, gymnocephalous, virgulate, parapleurolophocercous, pleurolophocercous and megalurous cercariae. Parapleurolophocercous cercariae constituted the most common type of cercariae recovered, contributing 41.2% of all infections in snails. Echinostome metacercariae infections were found in 6 snail species with 7.6% prevalence. In addition, the metacercaria of avian trematode, Thapariella sp. were found in Filopaludina spp. snails and B. funiculata with a prevalence of 0.5%. This is the first report for Thapariella metacercariae in the snail host, B. funiculata, and also confirmed that viviparid and bithyniid snails act as the second intermediate hosts of this trematode. This work will provide new information on the distribution and intermediate host of trematode in this area.

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.

IntroductionStellantchasmus falcatus, a species of fluke in the Family Heterophyidae, is a minute intestinal trematode of fish-eating birds and mammals. Human infections with this fluke have been reported in Hawaii [1], Philippines [2], Japan [3], Thailand [4] and Korea [5]. The S. falcatus metacercariae or infective stage is commonly found in freshwater fish such as Mugil sp. [5], Xenetodon cancila [6] and Dermogenus pusillus [7]. In Thailand, five species of flukes i.e. Haplorchis pummilio, H. taichui, H. yokogawai, S. falcatus and Centrocestus caninus were found responsible for human infections [8,9] due to the consumption of raw or undercook fish.Some medical properties of bitter cucumber (Mormordica charantia Linn.) include antiviral, antibacterial, anti-inflammatory, immunestimulant, insecticidal and anthelmintic properties. A bitter cucumber has been used to study about the anthelmintic activity on Ascaridia galli and Plasmodium berghei as antimalarial agent. A bitter cucumber (M. charantia Linn.) was shown that it was safe in experimental animals when ingested at low doses up to 2 months [10]. Previous study has confirmed that various preparations of papaya (Carica papaya Linn.) seeds can against helminthes effectively in vitro and in infected animals. Bioactive compounds responsible for the anthelmintic properties were ascribed to carpaine, carpasemine and benzyl isothiocyanate [11]. Most importantly, both papaya seeds and bitter cucumber fruits are cheap and easily available in tropical countries. However, there is no report that study regarding the effect of both extract of papaya seeds and bitter cucumber fruits on tegumetal surface of helminthes. Thus, this study is the first paper that study anthelmintic activity of both papaya seeds and bitter cucumber fruits on S. falcatus by observation under a Scanning Electron Microscope (SEM). Materials and Methods Preparation of the aqueous extract of papaya seeds and bitter cucumber fruitsThe aqueous extract of papaya seeds and bitter cucumber fruits were prepared according to the Thai Pharmacopoeia. Papaya seeds, 0.75 grams were dried and boiled in distilled water until the volume was 200 ml (3.75 mg/ml) then filtered through a sieved cloth to obtain a 100% stock solution. Twelve grams of bitter cucumber fruits was chopped and boiled in distilled water until the volume was 200 ml (60 mg/ml) and then filtered through a sieved cloth to get a 100% stock solution. The 100% stock solution was diluted in Tyrode's solution to give 12.5% and 50% concentration. Adult Stellantchasmus falcatus preparationThe chicks (Gallus gallus domesticus) were orally force fed with half-beaked fish (Dermogenus pusillus) infected with metacercariae of S. falcatus. Three days later, adult worms were collected from the small intestine of the chicks with Baremann's apparatus and washed with 0.85 % NaCl solution. The worms obtained were stored in Tyrode's solution. Experimental designThirty adult worms were individually incubated in Petri-dish containing 5 ml of Tyrode's solution, 12....

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