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Debate on antibiotic residues in shrimp farming masks broader concerns

There is global concern about antibiotic residues in farmed food products — and the potential economic damage of import bans resulting from exceeding regulatory limits is huge.

Yet according to Stephen G. Newman, PhD, president and CEO of Aquaintech Inc., the financial repercussions of a year of lost production due to disease drives many farmers to use antibiotics to excess in Southeast Asia, the world’s foremost region for shrimp production. A lack of scientific approach in the industry is another issue, he said.

“All too often when farmers have animal health challenges, they have no idea what is actually going on,” he wrote in Global Aquaculture Advocate. “While a competent authority may isolate and identify potential pathogens, disease is often multifactorial with multiple pathogens and stressors playing a role. Few farmers, if they look at all, look further than a single possible culprit.”

Instead, small farmers with their livelihoods on the line may risk using heavy doses of antibiotics. The common practice of “pooling” harvests makes this especially likely, he said, as it severely limits the traceability of compounds from different shrimp populations.

Loss of efficacy, resistance the ‘real issues’

Despite international concerns over residues, the real issues are antibiotic efficacy and resistance, their appropriateness for use in farmed animals, and farmers resorting to compounds designed strictly for human use, Newman wrote.

For antibiotic residues in shrimp to affect humans, he said it would be necessary to consume a quantity of shrimp so large as to be virtually impossible.

“To get the equivalent of a therapeutic dose (orally), say a gram, one would have to ingest 1,000 MT of shrimp,” he said. “Clearly this reduces the risk to as close to zero as one can get from having an adverse reaction to the presence of a residue.”

The greater concern is that administering heavy doses of antibiotics in shrimp farms reduces efficacy — and not just of the compound in question.  Through the transfer and fusion of plasmids between different bacterial species, the pathogens may become resistant to other antibiotics as well.

Effective antibiotic treatment depends on proper quantity and timing, Newman stressed. Though resistance occurs even with responsible practice, it is a much greater risk when using improperly high doses, shorter application times and stopping use when symptoms are no longer observed.

Alternating antibiotic types and monitoring resistance can help, Newman said, but such practices are not widely followed.

New residue standards needed

Making physicians accountable for what they prescribe is more achievable than holding shrimp farmers to account, he said. However, he questioned whether such accountability could be achieved with current priorities in residue testing: a zero-tolerance approach ignores the fact the antibiotics, properly administered to address the underlying cause of disease, can be very successful.

Furthermore, he added, shrimp ponds also contain many metabolic byproducts excreted by shrimp that are not tested for, including the non-protein amino acid BMAA, which is associated with neurological disorders.

“The reality is that the proper and appropriate use of antibiotics across the spectrum is not a realistic goal,” he said. “The double standard regarding the safety of food containing residues will persist until there is a universal, binding agreement by all parties to focus on residues of any number of compounds, not just antibiotics, and to develop methods that can detect most…of the violators.”

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