The causal linkages between the use of antibiotics in animals and the spread of antibiotic resistance in humans involve complex ecological processes, including the development of resistance, within- and between-species spread, circulation amongst animal and human populations, and the behavioral and economic conditions that foster or inhibit this circulation and spread. This study will look at the ecology and evolution of the spread of antibiotic resistance in northern coastal Ecuador, where road-building and deforestation are leading to an influx of small-scale poultry farming in rural communities. The study area offers a unique opportunity to investigate the role of the environment in the evolution of antibiotic resistance at the household, village and landscape scales and will draw on our expertise in molecular and microbial ecology, epidemiology, mathematical modeling, and ethnography.
Intensive antibiotic usage in animal husbandry is a major contributor to the growing problem of antibiotic resistance worldwide, posing threats to both animal and human health. Understanding the ecological processes involved in the emergence and spread of antibiotic resistance is crucial in designing effective intervention programs. The research team will include graduate students at the University of Michigan and the Universidad San Francisco de Quito (USFQ). There will be training and periodic health education workshops for community health workers, and the sharing of findings with health ministry employees at the local, provincial and national levels in Ecuador.
Intensive antibiotic usage in animal husbandry is a major contributor to the growing problem of antibiotic resistance worldwide, posing threats to both animal and human health. The causal linkages between the use of antibiotics in animals and the spread of antibiotic resistance in humans involve complex ecological processes, including the development of resistance, within- and between-species spread and the behavioral and economic conditions that foster or inhibit this spread. Our study took place in northern coastal Ecuador, where road-building and deforestation are leading to an influx of small-scale poultry farming in rural communities. This context provides a unique opportunity to examine the ecology of antibiotic resistance (AbR) evolution and spread. Results observable in this small-scale system can be generalized to other contexts through mathematical models. Our overall goal was to examine the ecology of AbR in human and animal populations, emphasizing how antibiotic (Ab) consumption by animals contributes to AbR in humans. We published a framework for the evolution and spread of antibiotic resistance in the American Journal of Epidemiology that provided guidence for model selection to study the transmission of AbR bacteria. We also published a commentary in The Lancet on the role of the social sciences in studying emerging infectious diseases. We have one manuscript under review showing that the prevalence of antibiotic resistance is highly dependent on both the rate of onset of antibiotic use as well as the duration of antibiotic use. A second manuscript examines the influence that disease prevalence in neighboring communities has on a given community, both in terms of that community’s incidence levels and transmission pathways that are causing disease. This research project has involved many students from a wide variety of backgrounds. At Michigan, we involved undergraduate and graduate students and a post-doctoral fellow. At Trinity we have had undergraduates, and at Emory a mixture of undergraduates and master’s students. In Ecuador, we trained and mentored several masters level students, which will open up opportunities for them to go on to doctoral level training internationally. We also involved members of the local Afro-Ecuadorian and Chachi communities in our research, providing opportunities for them to increase their capacity to obtain future employment, or to save money to be able to attend college. Although traditionally chickens were exclusively free ranging in this part of Ecuador, the introduction of roads in this region has led to an emerging local industry where chickens are farmed using feed that contains antibiotics. We found that farmed chickens were much likelier to have high rates of AbR than free-range chickens. When comparing human resistance patterns with those of chickens we observed that, in general, the prevalence of antibiotic resistant E. coli in chickens is higher than in humans, especially for quinolones and gentamicin. But although chickens had higher prevalence of AbR than humans, we saw high resistance levels in animals and humans for the same antibiotics. For example, the six antibiotics with the highest levels in chickens were also shown to be the highest in humans. Likewise, the lowest three antibiotics observed in chickens were also the lowest observed in humans. This suggests that either resistance is flowing from chicken to humans or humans to chickens, or that both chickens and humans have a common selection pressure. These ecologic data, therefore, provide some evidence for a linkage between chickens and humans. Because of the noticeable difference in antibiotic use between humans and chickens in the region, the similar resistance pattern seen in humans and chickens is not likely to be entirely the result of the same selective pressure. To describe how antibiotic resistance emerges in chickens, we did a controlled study in an experimental facility. Since antibiotics are heavily used in this chicken hatchery, newly hatched chickens already have significant levels of antibiotic resistant bacteria. Resistance levels increased from Days 1-21 across 9 antibiotics tested, but generally decreased from Days 21-38. Only 5 genotypes persisted within the same chicken between time points 1 and 2 compared to 47 between times 2 and 3. This provided evidence for a change in selection pressure and exposure when the chickens moved from the hatchery to the experimental site. Project investigators have lectured about the project to audiences at various Schools of Public Health in the United States, Ecuador, and Brazil, as well as to USAID in Washington, DC. In Ecuador we conducted town meetings in every village to discuss the relevance of our work to the community and to give educational talks on health-related issues. Photos, village maps, summaries of village census and network data, and summaries of disease prevalence and incidence were distributed. Materials were reworked so as to be intelligible to audiences with limited formal education. We prepared a summary of village statistics for village leaders to use in applications for provincial, national, or foreign development assistance.
