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

Aestivation and its impact on the survival of snail intermediate hosts and trematode transmission in rice paddies

In this study, we investigated the diversity and survival of aestivating snails in dry-season rice paddies, focusing on their role as intermediate hosts for trematodes. A total of 1,159 snails from various families were collected and analysed, revealing nine species, primarily from the Bithyniidae family, with Bithynia siamensis siamensis being the most abundant. Of the nine species collected, the most common species, B. s. siamensis, exhibited a relatively high survival rate of 81.5% throughout the three-month dry period post-harvest, whereas the remaining eight species had survival rates below 24.0% (0-23.1%). Four snail species, B. s. siamensis, Filopaludina martensi martensi, F. sumatrensis polygramma, and F. doliaris, were found infected with larval trematodes, with an overall prevalence of 8.46% (57/674). The larval trematodes identified were categorized into four types: echinostome metacercaria, Thapariella anastomusa metacercaria, unidentified metacercaria, and unidentified rediae. These findings demonstrate that trematode infections can persist in aestivating snails despite the challenging conditions during the dry season, emphasizing the potential of aestivating snails to act as vectors for trematode transmission in agricultural settings. This underscores the need for effective management strategies to mitigate the risks associated with trematode transmission.

Limiting the spillover of zoonotic pathogens from traditional food markets in developing countries and a new market design for risk-proofing

Traditional food markets are age-old systems that primarily serve the food supply needs of society's less affluent sectors, often operating with minimal infrastructure. These markets are prevalent in low and middle-income countries. However, their hygienic conditions are frequently suboptimal, potentially fostering the emergence and spread of presumptive zoonotic diseases. The recent emergence of zoonotic or potentially zoonotic diseases and their possible links to traditional food markets underscore the need for focused attention on this overlooked issue. The socioeconomic characteristics of traditional food markets reveal that despite the risk of zoonotic pathogen spread, these markets play a crucial role for large segments of the population. These individuals rely on such markets for their livelihood, food, and nutrition. Therefore, a comprehensive set of measures addressing various aspects of traditional food markets is necessary to manage and mitigate the risks of potential zoonotic disease emergence. In this article, we explore various facets of traditional food markets, paying special attention to the risks of zoonotic diseases that urgently require stakeholder attention. We also propose a new market design to prevent the risk of zoonotic spillover and advocate for the development of a Market Hygiene Index for these markets.

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

We investigated diversity, infective situations, morphological features and phylogenetic relationships of the metacercariae in freshwater snails from Bangkok between March 2018 and February 2020. Crushing and dissection techniques were performed to explore the metacercariae in the snail hosts. Polymerase chain reaction was implemented to amplify the internal transcribed spacer 1 (ITS1), 5.8S ribosomal DNA and ITS2 regions of metacercarial DNA. A total of 3173 of all 21 707 snails showed infections with metacercariae, representing a relatively high infective prevalence (14.62%) compared to earlier research. All infected snails belonged to 14 species/subspecies. A group of viviparid snails exhibited the highest metacercarial infections (26.10–82.18%). We found metacercariae with seven morphological groups. Five of them can be stated as new records of the metacercariae in Thailand, indicating a broader spectrum of larval trematode diversity. Our phylogenetic assessments established that five of the seven morphological groups can be molecularly classified into different taxonomic levels of digenean trematodes. Echinostome A metacercariae revealed the highest infective prevalence (7.15%), and their sequence data were conspecific with a sequence of Echinostoma mekongki, which is a human intestinal fluke; this finding denotes the distribution and suggests epidemiological surveillance of this medically important fluke in Bangkok and adjacent areas. However, two groups of Opisthorchiata-like and renicolid metacercariae remain unclear as to their narrow taxonomic status, although their molecular properties were considered. For more understanding about trematode transmissions in ecosystems, both physical and biological factors may be further analysed to consider the factors that relate to and contribute to trematode infections.