The scourge of antibiotics in animal feed
The inappropriate use of antimicrobials in animals is thought to be a leading cause of the rise in antimicrobial resistance, the UN General Assembly said in a landmark statement in 2016.
We are making breakthrough innovations and we have tools… to essentially change the paradigm on how we look at anti-infectives. – Cyril Gay, US Department of Agriculture
While it is the livestock in higher-income, meat-consuming nations that dominate the consumption charts, antibiotics are more easily available in lower and middle-income countries – and their use is harder to document, as Nguyen demonstrated. Researchers are finding worrying levels of resistance to antibiotics in farm animals in poorer countries, he says. And with rising human populations ever hungrier for meat, farming is intensifying and increasingly dependent on antimicrobials.
“There’s a really high burden of infectious disease already in the Global South,” says Chris Creese, a communications specialist who works with the Food and Agriculture Organization (FAO). “If farmers just stopped prophylactic use on a dime then there’s this risk of infection proliferation, which is a livelihood issue but also a public health threat.”
There are several routes by which resistance on farms could translate into human diseases becoming more resistant to drugs. The biggest worry is that antimicrobials are flooding out of farms in effluent, turning the environment into a cooking pot of drug-resistant microbes of all kinds.
A dose of silver
To tackle the problem, in 2015 the World Health Organization, the World Organization for Animal Health (OIE) and the FAO published a global action plan on antimicrobial resistance (AMR), pressing countries to develop national action plans, and for these to include livestock strategies. And in April, a UN interagency report on AMR called for the phasing out of growth-promoting antimicrobials in agriculture, with an immediate ban on using antibiotics of critical importance to humans.
Some countries have passed legislation. In January, Vietnam joined a growing list of countries that have prohibited manufacturers adding antibiotics to feed. But legislation can be hard to enforce, says Nguyen, particularly if there is no alternative. “People… understand that the more [antibiotics] you put [in], the more the pig is healthier and grows faster,” he says.
Nguyen has been experimenting with an alternative antimicrobial that he thinks could avoid the resistance issues: nanosilver. In an unpublished pilot study, he found that two groups of pigs – one fed with antibiotic and one with tiny particles of silver – differed little in their levels of growth and disease.
Silver nanoparticles have been shown to have effective antibacterial activity against a range of disease-causing bacteria.
Although there are concerns about the safety of nanomaterials, such as possible toxicity, other nano-replacements are emerging. For example, particles of polystyrene can bind bacteria together in the gut, forming clumps that are then excreted.
Worldwide, the search for alternative feed additives is heating up. “We are making breakthrough innovations and we have tools … to essentially change the paradigm on how we look at anti-infectives,” Cyril Gay at the United States Department of Agriculture, told a meeting of the OIE in 2018.
Front-runners include prebiotics – nutrients that nourish beneficial bacteria in the gut – and probiotics – doses of the beneficial bacteria themselves. One problem is that it’s not clear how probiotics work, says Gay. It might be by out-competing more damaging bacteria in the gut; or it might be that the bacteria release anti-infective agents. Working this out is crucial so that they can be used rationally, he says.
But that hasn’t stopped farmers and manufacturers adopting them. They have been used successfully in shrimp farms in Thailand, and Nguyen is about to pilot them in a feed trial.
Meanwhile, the search for alternative treatments includes rifling through the thousands of compounds found in plants. People claim various compounds are effective antimicrobials all the time, but the mechanisms of action and potential toxicity are unknown, says Gay.
Elisabeth Erlacher-Vindel, an antimicrobial resistance specialist at OIE, is concerned about “one-year wonders” emerging on the market that later turn out to be ineffective. “A lot of people have started using plants and all kinds of things but nobody evaluates,” she says. “We really want to invest in this as well because telling people to stop using things will be very difficult.” An OIE conference in Bangkok, Thailand, in December will scrutinise some of these touted alternatives.
The UK’s Fleming Fund has been supporting research in 12 African and Asian countries that is revealing how antibiotics prop up a system lacking in vets, diagnostics, medicines and sanitary practices.
Creese, who has worked on the project, tells of an eight-year-old Maasai pastoralist’s son in Tanzania sent to the vet to fetch antibiotics for a sick cow. “There’s no inspection of the animal, there’s no proper diagnosis, there’s not a consideration of whether that antibiotic is an important one. There isn’t the infrastructure to support prudent use.”
So much can be done on farms to reduce infection levels, says Daniela Battaglia, livestock production officer at the FAO. Switching to locally adapted breeds inured to local diseases, and vaccination, are important strategies. So are a host of biosecurity measures: keeping animal feed dry and water clean; good nutrition and ventilation; separating sick animals and restricting human access. Other key measures are promoted in the FAO’s Top Ten Actions for Farmers guidelines.
But it can be hard to drum up motivation to change, says Creese. “If you take something as simple as a footbath [which assists in the prevention and treatment of hoof diseases] … farmers know that it’s important to have them but … it’s really hard sometimes to justify all these additional expenses when you don’t see what the gain is.”
Philip Mathew, a public health consultant for the NGO ReAct Asia-Pacific, agrees. In Kerala state, India, ReAct is most concerned by intensive poultry production where tens of thousands of chickens are reared in cramped quarters, disease often warded off by antibiotics. “There is no incentive for a farmer to produce antibiotic-free food,” he says.
Mathew claims that better chicken housing, with ventilation and pest control measures built-in, would pay for itself in improved yields within a year. He would like to see loans available for such investments, and insurance that could help farmers tolerate the risk of going antibiotic-free.
For Nguyen, too, it’s a question of changing the incentives in the system. “In Vietnam many vets are working for feed companies or vet companies… their income relies on how many vet drugs they are selling… we need to see how they can get enough earnings but not rely on selling as much as possible to farmers.”
Ultimately, however, if changes aren’t made now, they will be made in a rush when antimicrobials really begin to fail.
“We can pay less now or more later,” says Creese. “Change is coming. Whether we like it or not.”