Tasmanian Salmon Antibiotics Could Create Health Crisis

Our Tasmanian farmed salmon industry is seeking fast-tracked approval to use the antibiotic Florfenicol to combat the bacterial disease, Piscirickettsia salmonis (P. salmonis).

This disease has been circulating in salmon pens, particularly in southern Tasmania’s D’Entrecasteaux Channel, following a mass mortality event during the summer. Although departmental staff describe the disease as ‘endemic’ rather than an ‘outbreak,’ crossbench MPs claim a worsening situation. The industry previously used oxytetracycline, and an EPA report found residues of this antibiotic in wild fish, specifically blue mackerel, near a salmon lease.

The industry is now pushing for Florfenicol, which Primary Industries Minister Gavin Pearce supports, noting that oxytetracycline has “limited uses.”

Tasmanian Times brings you an article translated from Spanish written by Felipe Cabello 29 June 2023.

In recent weeks, the environmental problems generated by the expansion of salmon farming [in Chile] into so-called “potentially protected” geographical areas have been widely exposed in the media.

The discussion included, albeit marginally, the mention of the biodiversity problem generated by the increase in resistance to antimicrobials (antibiotics), which in addition to affecting the aquatic environment, also negatively affects animal health and that of people.

This problem is generated because the feed of salmon in industrial farming may contain antimicrobials, used to prevent and treat infections.

It is a topic that evolves in the microscopic world, invisible to the naked eye, and its catastrophic results on human health are revealed belatedly in doctors’ offices and hospitals, far from the aquatic environment.

However, microbiological science, with its concepts and methods, helps us to visualise the evolution of these practically invisible phenomena, and to overcome the apparent physical barrier that would exist between the aquatic and the terrestrial. Salmon farming is the human activity that uses the most antimicrobials in the country. The solid canons of microbiological science indicate that they contribute to the selection of bacteria resistant to these therapeutic, life-saving compounds; in a process that, by eliminating the bacteria that are sensitive to them, causes microbial biodiversity to decrease. This results in several negative aspects, of which resistance selection is the most axiomatic.

In 2020, salmon farming used, in addition to other antimicrobials, approximately 360 thousand kilograms of phenyls (florfenicol), while human medicine used about 100 kg (chloramphenicol).

In other words, salmon farming used 3600 times more of these drugs than human medicine (while the latter should be understood as extending to the entire country, the former is limited to limited areas of Patagonia).

The geographic concentration of this colossal use of antimicrobials, and the fact that phenicals and others degrade slowly, causes them to accumulate in the aquatic environment for a long time, selecting bacteria with resistance genes and facilitating their dissemination, for months and years. This intense and permanent selective pressure, given the physical organisation of resistance genes, also means that antimicrobials that have never been used in salmon farming are selected for resistance, generating bacteria with multiple resistance to them (the so-called “superbugs”).

The resistance-selecting impact of this use on bacteria in the aquatic environment—including sediments, water, salmon, wild fish and farmed mussels—has been repeatedly demonstrated by various researchers and with various methods.

In 1958, the Nobel Prize in Medicine was awarded to Professor Joshua Lederberg (33 years old) for his early experiments that demonstrated the presence of sexuality in bacteria and their ability to transmit genetic information to each other, such as antibiotic resistance. Professor Lederberg’s discovery allows us to understand why resistance genes that are selected by salmon farming in the aquatic environment can be transmitted to terrestrial bacteria, including human pathogens diagnosed in doctor’s offices and hospitals.

The ability of resistance genes to spread among various groups of bacteria, including pathogens, makes it difficult to treat bacterial infections, increases their complications, and also increases their mortality and the cost of treatment.

For his discoveries to explain the spread of antimicrobial resistance, in addition to the health impact on disease and death of this resistance, Lederberg – with whom I fortunately had multiple scientific and social interactions at Stanford University – became a champion in the fight against the indiscriminate use of antimicrobials until the end of his days.

In a tribute celebrating Lederberg’s fundamental microbiological contributions, another Stanford professor, S.N. Cohen, (with whom I worked on the resistance problem for several years) said:

“It is remarkable that despite the enormous progress in the treatment of infectious diseases during Joshua Lederberg’s lifetime, the ominous problem of bacterial infections and their resistance to treatment is still a major current problem.”

In this way, the WHO has called antimicrobial resistance a silent epidemic, which kills approximately five million people each year (more than malaria or AIDS), with a health cost of billions of dollars.

The validity of this problem in Chile is indisputable, and has been demonstrated by numerous studies.

The fundamental role of salmon farming in the evolution of this health threat is also undeniable. In Patagonia, the high levels of bacterial resistance in the aquatic environment, including in salmon, are undoubtedly anthropogenic, and the presence of resistance in human pathogens in hospital and clinic patients is one of the results of this indiscriminate use of antimicrobials in salmon farming.

The industry justifies its reckless practices in this regard by the presence of the fish pathogen Pisciricketsia salmonis.

However, various reports seem to suggest that it is, above all, widespread and uncontrolled overproduction that is the main cause of high fish mortalities due to infections.

The sustained culture of fish at high and unhealthy concentrations stresses and immunosuppresses them, facilitating their infection by bacterial, viral and parasitic pathogens. Bacterial infections are being prevented with the intensive use of antimicrobials without great success, as they continue to cause great losses due to resistance to these compounds and the atrocious farming conditions of salmon, which apparently disrespect minimum animal welfare safeguards.

This problem only confirms the relationship differences between animal and human health and the integrity of the environment, which we must understand under the concept of One Health.

Parliamentarians from Patagonia – apparently ignorant of microbiology – have unreservedly supported the expansion of salmon farming into protected areas, arguing for conservation and increased employment.

But a precondition for employment is to be alive, healthy and free of untreatable infections, which salmon farming in the region undermines. The expansion of salmon farming in the conditions described will further deteriorate human and fish health in the territory, together with the assault on biodiversity that this entails, which will probably repeat phenomena of environmental, social and economic catastrophe such as those of 2016 in Chile.

We need to expand and understand microbiological knowledge to protect the biosphere and life in it:

Salux populi suprema lex. [Latin for ‘the health of the people is the supreme law‘]

Felipe Cabello is a Professor of Microbiology and member of the American Academy (United States) of Microbiology. For more than forty years he has worked on various aspects of Sorantimicrobial resistance, from the molecular to the epidemiological, with publications on the subject.

Authors note: The elaboration of the concepts summarised in this article has been the result of the exchange and suggestions of countless colleagues and was partially funded with a Guggenheim Fellowship, USA/Canada and a project of the Lenfest Ocean Program/Pew Charitable Trust.

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