Fish farmers in north-east Thailand are dosing tilapia with antibiotics of unknown origin and strength, directly into shared rivers where wild cattle and people also draw water. This matters because antimicrobial resistance (AMR) is rising globally, and aquatic environments are a poorly understood pathway for resistance to spread between animals and humans. Aquaculture is a major food sector in South-East Asia, yet the relative contribution of fish farming to environmental AMR—compared with other sources—has never been systematically quantified. Without that data, regulators cannot design effective mitigation strategies or know whether those strategies work. The team will measure antibiotic residues and resistant bacteria upstream and downstream of fish farms, compare them with control sites, and use genomic fingerprinting to trace whether resistant *E. coli* found in wild cattle, domestic livestock, and local people share a common origin in aquaculture. They will also survey farmers’ antibiotic practices and test which intervention options—such as improved feed or protective equipment—farmers would actually adopt. If successful, the study will produce the first quantified risk profile for aquaculture-driven AMR in a Thai watershed and a stakeholder-validated intervention pathway. That pathway could inform regulatory policy across South-East Asia’s freshwater food systems.
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The rapid global rise in antimicrobial resistance (AMR) is a critical public health crisis. It is widely acknowledged to be a One Health challenge, with aquatic environments playing a role of in the development and spread of AMR to people and animals. Aquaculture is an essential food production sector in South-East Asia; however, overuse of antibiotics and poor adherence to antibiotic treatment regimes are considered key contributors to rapid AMR development in the aquatic environment. This includes several classes of antimicrobials essential to treat human infections that are delivered to fish through medicated feed directly in shared waterbodies. Despite these concerns, the risks associated with environmental AMR – including the relative contribution of aquaculture – are poorly characterised and quantified, making it challenging to devise appropriate mitigation strategies or assess their effectiveness. This study will apply a One Health approach to elucidate the contribution of aquaculture production to environmental AMR and the subsequent risks for people, using the Pao River watershed in north-eastern Thailand. In this region, tilapia farming in open cages is commonly practiced and our team has documented high levels of unregulated antimicrobial use, wherein farmers frequently use products with unknown formulations or products not necessarily developed for use with fish. The risks that this poses for driving the selection for AMR are unknown. Moreover, antibiotic-treated feed is commonly prepared without the use of appropriate personal protective equipment such as masks and gloves, representing a potential risk for heightened AMR in fish farmers. Also in this watershed, our previous study revealed high levels of multi-drug resistant E. coli in banteng – a species of wild cattle – compared with local domestic cattle. This has led us to hypothesise that wildlife and people are at risk of acquiring AMR through this shared water source as a consequence of antibiotic use in aquaculture. To characterise and quantify these risks, we will: Assess the relative contribution of different sources of AMR to the Pao River watershed, and determine the degree of sharing of AMR bacteria/genes across the One Health spectrum. This will be done by i) measuring concentrations of antimicrobial residues and types/levels of resistant bacteria up- and down-stream of fish farms and compared with control sites without aquaculture; and ii) determining the AMR profiles of two key indicator bacterial species isolated across the One Health spectrum within the watershed (i.e. from samples collected from people, livestock, wildlife, fish) to assess for the specific contribution of aquaculture amongst other potential sources of AMR. This will be investigated through a combination of phylogenomic approaches and source attribution modelling. Characterise the practices and risks related to antimicrobial use in aquaculture as a potential driver for AMR in the aquatic environment. This will include measuring the quality and quantity of antimicrobials used, how they are administered, and what is driving these treatment decisions. We will assess likely uptake of different intervention options for improving antimicrobial stewardship through a stated-preference choice experiment. Based on the key risks identified, potential interventions to reduce the development and spread of AMR will be co-developed with multiple stakeholders, incorporating regulatory, political, economic and social dimensions. Overall, this study will generate new knowledge on AMR risks from aquatic food production and lead to an intervention pathway.
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