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Computer-generated image of bacteria that produces whooping cough. Credit CDC/Unsplash

New tool weighs costs and benefits of managing evolution of pathogens and pests

16 November 2021

Spend money now on antibiotic stewardship practices or save the money but run the risk of potentially deadly antibiotic-resistant bacteria emerging later? A new economic tool can help physicians, farmers and other people whose activities may influence the evolution of biological organisms, such as pathogens and insects, decide when they should invest in evolution management strategies.

The model, developed by an international team of scientists and published today (Nov. 16) in the journal PLOS Biology, suggests that managing evolution is beneficial if the increase in the lifespan of the product — for example, an antibiotic or a pest-resistant crop — that results from management is larger than the increase in profit that could be obtained currently by not managing evolution.

“The bottom line is that there is a simple relationship defining when it is worth investing in evolutionary management. And it turns out, that the break-even point is surprisingly modest,” said Andrew Read, Evan Pugh Professor of Biology and Entomology and director of the Huck Institutes of the Life Sciences, Penn State. “The management doesn’t have to be all that effective and it’s still worth it. We encourage people to implement practices now that will not only protect their products and profits over the longer term, but also help to protect human health and well-being.”

According to the researchers, human behavior often drives the evolution of biological organisms in ways that can profoundly adversely impact human welfare. For example, by using crops that are genetically modified to produce toxins from the fungus Bacillus thuringiensis (Bt) as a way of deterring pests, farmers can unintentionally increase the number of insects that are resistant to the toxin, thus rendering the use of Bt as a pest control strategy ineffective. In another example, the overuse of antibiotics in hospitals can lead to the proliferation of resistant bacteria, which can hamper our ability to treat infections.

Read explained that several evolution management strategies already exist. With Bt crops, farmers can set aside areas for growing non-Bt-crops so that Bt-susceptible insects have a refuge to reproduce. This strategy, he said, has been shown to more than double the lifespan of Bt crops before Bt-resistant insects gain the upper hand. Similarly, the implementation of antibiotic stewardship policies in hospitals, such as using antibiotics only when necessary and optimizing the dose amount and duration of treatment, can lengthen the lifespan of life-saving antibiotics.

“The problem is that people often forgo evolution management because of the upfront costs of investing in it,” said Read. “But our new model demonstrates that in most cases the benefits of evolution management outweigh the costs.”

The centerpiece of the team’s new analysis, said lead author Troy Day, professor of mathematics and statistics, Queens University, is a mathematical formula that determines when physicians, farmers and other “evolution managers” will have sufficient incentive to manage the biological resources that are under their control, trading off the short-term costs of stewardship against the long-term benefits of delaying adverse evolution.

“For instance,” added David Kennedy, assistant professor of biology, Penn State, “when a patient arrives in an urgent-care facility, screening them to determine if they are colonized by a dangerous ‘superbug’ [or antibiotic-resistant bacterium] is costly, but protects future patients by allowing superbug carriers to be isolated from others.”

In addition to projecting the course of evolution of biological organisms under different scenarios, as well as company or owner profits, the model also examines the effectiveness of potential policies that could encourage evolution management, such as taxation strategies or government subsidies. To do this, the researchers incorporated game theory — an economic tool for analyzing how individuals’ decisions can impact others, such as hospitals in the same area whose patients can infect each other or corn farmers with neighboring fields owned by other farmers. Their game-theory analysis identifies conditions under which outcomes can be improved through policies that change incentives or facilitate coordination among individuals.

“In the example of antibiotic-resistant bacteria, hospitals could go above and beyond to control the spread of superbugs through methods like community contact tracing,” said David McAdams, professor of business administration, Duke University. “This would entail additional costs and, alone, a hospital would likely not have an incentive to do so. But if every hospital took this additional step, they might all collectively benefit from slowing the spread of these bacteria. Game theory gives you a systematic way to think through those possibilities and maximize overall welfare.”

The team concluded that evolution management can be economically beneficial under a remarkably wide range of conditions.

Kennedy said, “Our research shows that taking actions to manage evolution can go hand in hand with maximizing profit.”

The Science and Technology Directorate, the Department of Homeland Security, the Fogarty International Center, the National Institutes of Health, the Natural Sciences and Engineering Research Council of Canada, and the Institute of General Medical Sciences supported this research.