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11.9 Evolutionary biology can help manage antibiotic and insecticide resistance

The pathogens and insect disease vectors, such as mosquitoes, that we are trying to control evolve in response to selection we create by using antibiotics or insecticides. Adopting common-sense measures to limit infections and infestations, and to reduce the chances of resistance genes increasing in frequency offers the best hope of a long-term solution.

Prevention and Appropriate Treatment

Because the likelihood increases that bacteria will evolve resistance to antibiotics each time we use such treatment, it pays to try to prevent infections in the first place. For example, good hygiene in medical care facilities and in the home can reduce the spread of infectious disease. Reducing the rate of infection decreases the need for treating patients. Having to treat fewer patients lowers selection pressure on pathogenic bacteria for antibiotic resistance. When treatment with antibiotics is necessary, appropriate treatment is essential. Antibiotics should be used only when they can benefit the patient and should target a specific pathogen. In addition, the antibiotic must be taken in the appropriate dosage and for the full length of time prescribed for effective treatment.

Lower Antibiotic Use in Livestock Production

Reducing the use of antibiotics in livestock production can also lower the prevalence of antibiotic resistance among bacteria in meat products and animal waste without compromising the welfare of the industry. For example, the amount of antibiotics given during the production of a kilogram of meat in Denmark, the world’s leading exporter of pork, is one-sixth that given in the United States. Concerned about the growing problem of antibiotic resistance, Denmark banned the use of antibiotics as growth promoters for livestock in 1998. Since then, the antibiotics used in Denmark’s highly industrialized livestock production systems can only be administered to treat illness and upon prescription by a licensed veterinarian. As a result, the amount of antibiotics administered to livestock in Denmark has been cut in half.

Why might some agricultural interests oppose changing the use of antibiotics in meat production in the United States?

To combat disease, Danish livestock producers now rely less on antibiotics and more on preventative hygiene—for example, more frequent cleaning of pens, better ventilation, and reduced crowding. Adjustments such as these have increased the costs of production by less than 1% and the meat-producing industry in Denmark continues to grow. Meanwhile, the occurrence of antibiotic-resistant bacteria in livestock and meat products in Denmark has decreased dramatically (Figure 11.22 below).

RESISTANCE DECLINE IN BACTERIA FROM PIGS

FIGURE 11.22 The use of macroclide antibiotics declined rapidly after Denmark’s 1998 ban on the use of antibiotics as growth stimulators. Following that decrease, the occurrence of resistance to macroclide antibiotics in the bacterium Campylobacter coli in pigs also decreased significantly. (Data from Pew Charitable Trusts, 2013)

Surveillance Is Essential for Managing Resistance

What role can the business community play in efforts to control malaria in Africa and elsewhere?

Surveillance, or monitoring, of pest and pathogen populations aimed at detecting the appearance and prevalence of resistance is essential to any program aimed at limiting antibiotic or insecticide resistance. As we saw in Chapter 7, monitoring of pest populations is critical to effective Integrated Pest Management in agricultural settings (see page 221), and it is just as important to controlling disease vectors. A surveillance program that detects the appearance of resistance early permits a timely and effective response. An early response, such as switching to an alternative antibiotic or pesticide, is essential to prevent resistance from becoming too frequent in pest and pathogen populations.

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Diversifying Chemical Treatments

Developing a diversity of antibiotics and insecticides with different modes of action is crucial for combating resistance. In their attempts to control malaria vectors, researchers have identified several new insecticides that are highly effective against populations of malaria-transmitting mosquitoes. Of particular interest are those new insecticides that are effective at controlling mosquito populations now resistant to pyrethroids and DDT. For example, controlled studies in Benin, Africa, conducted by researchers from the London School of Hygiene and Tropical Medicine and local scientists have demonstrated the effectiveness of an inexpensive, long-acting substitute for DDT and pyrethroid insecticides for indoor spraying (Figure 11.23). This insecticide, chlorpyrifos methyl, which was developed by Dow AgroSciences, also has low toxicity to mammals and is rated as safe for indoor spraying. As we continue our quest for sustainable solutions, partnerships between research scientists, environmental health specialists, and business will be essential.

MORTALITY OF MOSQUITOES EXPOSED TO DIFFERENT HUT-SPRAYING TREATMENTS

FIGURE 11.23 A new insecticide, Chlorpyrifos methyl, shows promise for reducing malaria transmission by a population of the mosquito Anopheles gambiae known to be resistant to pyrethroid insecticides and DDT. (Data from N’Guessan et al., 2010)

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Think About It

Why should there be an evolutionary cost to antibiotic or insecticide resistance?
Is there likely to be any chemical defense against pathogenic bacteria or insect vectors of disease that will not eventually lead to resistance in the target population? Why or why not?
There are significant benefits to using large amounts of antibiotics in livestock production. What are the risks to people and the environment?

11.7–11.9 Solutions: Summary

A risk is anything with the potential to cause us harm or loss or put us in danger. Risk management practices include four basic steps: identification of the hazard, dose–response assessment, exposure assessment, and risk characterization. Based on risk assessment, the EPA phased out lead in gasoline and banned or limited lead used in consumer products such as residential paint.

The precautionary principle can be used as a tool for making better health and environmental decisions. It aims to prevent harm from the outset rather than manage it after the fact. Modern approaches to disease control go beyond vaccines and medicines to include cooperation among health organizations and governments, innovative research, education, and awareness of culture and values. The health risks associated with the bushmeat trade may be reduced by public health campaigns that emphasize the dangers of harvesting certain animals. Insecticide-treated mosquito nets and indoor spraying are being used to reduce the rates of malaria infection, especially among children and pregnant women. The principles of evolutionary biology can contribute to more sustainable control of pathogens and pests.