Can veterinary extension services reduce the risk of antimicrobial resistance on small stakeholder fish farms ?

 Small fish farm operators in low income countries can rarely afford the costs of private veterinary services. When there is a disease outbreak on one of these farms and there is no access to affordable health professionals with diagnostic capabilities, farmers will rely on their own knowledge, that of non-professionals, or pharmaceutical sales agents for treatment options and advice.  Further, farmers may not know how to properly deliver treatment products to their animals, especially on farms where the estimated biomass may not be accurate.  In these situations, the delivery of drugs, top coated on feed, can result in inadequate uptake, leaching, and environmental contamination with low levels of the products.

Can providing free diagnostic services and veterinary advice to these small farmers reduce the misuse of antibiotics and antimicrobial resistance (AMR) in the aquatic environment? Veterinary extension services for food animals are expensive to maintain, but if they help reduce the misuse of antibiotics they may be worth supporting.  

City University of Hong Kong (CityU) and the Agriculture Fisheries Conservation Department of the government of Hong Kong in 2018 initiated a subsidized aquatic animal veterinary service to help small stakeholder farmers improve their fish production and reduce the use of antibiotics on farms.  The veterinary service had a dedicated phone line for farmers to call if they wanted fish health advice.  When they called, we would send a veterinarian and a technician to the site to investigate, diagnose, and provide advice on mitigation strategies to address the issue. We made a point of responding to farmers in a timely manner, usually within 24 to 48  hours. We also had at least one follow-up visit or phone call to ensure the situation was under control. Local veterinarians and technicians were hired for this service to facilitate communication with local farmers in Cantonese, and by 2022 the aquatic animal veterinary service had over 80 clients.  We provided service to salt and fresh water aquaculture systems, including net pen sites, ponds, and recirculating aquaculture facilities. 

The range of aquatic animals we encountered included shrimp, grouper, pompano, jade perch, mullet, carp, tilapia, as well as number of other minor aquaculture species.   The most common issues we diagnosed were water quality problems, parasite issues, and bacterial diseases, with the latter usually secondary to water quality and or parasite issues. When we diagnosed a bacterial disease on a fish farm we conducted a sensitivity analysis and if appropriate (i.e. fish were on commercial pelleted feeds, were not close to market size, the bacteria was sensitive to one of the two antibiotics that we had in stock, the fish inventory was known, and the fish were feeding) we would recommend an antibiotic treatment to reduce mortality. To circumvent the purchase of less expensive counterfeit products from the internet by the farmers, the veterinary service also subsidized the cost of selected, approved drugs for fish use.  When we prescribed medication for the treatment of an infectious disease we always followed up with the farmer within a few days to ensure the fish were responding and, if they were not, we would revisit the farm to understand why the treatment failed.  These visits sometimes included additional diagnostic work.

Over time, we developed a trusting relationship with our clients and they began to change some of their management strategies to focus on prevention of diseases, including better monitoring of fish health and earlier detection of health issues.  The government of Hong Kong also requested  our service to provide workshops for farmers to address industry fish health issues once or twice a year. We based these workshops on the knowledge gaps that we identified from discussions with farmers during our site visits.  One of the first workshops we offered was on the prudent use of antibiotics on fish farms, which provided farmers with a baseline understanding of the issues related to treating fish with antibiotics and introduced some practical actions they could take to avoid treatment failure and AMR.  

In the article, we present the data on the AMR profile of the fish pathogens isolated by the veterinary service over a 4-year period.  Results suggested a reduction in the proportion of cases requiring antibiotics, and a decline in antimicrobial resistance associated with antibiotics formulated for fish use. In contrast, resistance to other drugs, likely used in human medicine, remained elevated.   

Although the initial purpose of the veterinary service was to increase the sustainability of the small aquaculture industry in Hong Kong and train veterinary students in fish medicine, it appears to have had several unexpected collateral benefits vis-à-vis AMR.  We believe the advice given during visits by the veterinarians has led to improved farming practices in Hong Kong, which has improved and probably reduced local antibiotic use.  Although this type of service is expensive it may be an effective way to deal with the misuse of antibiotics.