Research analyzes relationship between agriculture, emergence of new diseases

BLOOMINGTON, Ind. — Research from the Indiana University School of Public Health-Bloomington proposes a new way of understanding how diseases spread between animals and humans, by focusing on the effect that agriculture, ecological and sociopolitical factors have on disease emergence and transmission.

In an article published in the journal One Earth, the research team specifically considers how to minimize the emergence of zoonotic diseases, or new infectious diseases where pathogens are circulated between humans and domestic and wild animals. They recommend taking a more holistic approach and looking at broader factors that may be in play as new diseases sicken people.

“Right now, there is an oversimplification of the complex social reality that impacts disease spread,” said study co-author Luis Chaves, associate professor in the School of Public Health-Bloomington. “Most diseases are impacted by this. Why do we have transmission hotspots in certain areas but not others, despite having similar environments? It’s because both landscape change and how society works as a whole matter. Understanding this and reframing our thoughts is imperative to prevent future pandemics.”

“Many people assume that agriculture is always in conflict with biodiversity conservation, but that’s not always the case,” said co-author Ivette Perfecto, professor in the School for Environment and Sustainability at the University of Michigan. “It’s true that large-scale industrial monocultures are notorious for destroying biodiversity. As biodiversity declines locally, the normally species-rich collection of animals is reduced to a few species that are likely to harbor pathogens that may already be — or certainly have the potential to evolve into — pathogens that can infect.”

According to the researchers, there needs to be a focus on the agricultural matrix, or the landscape where food is produced, which includes both human-managed land and natural habitats.

“The agricultural matrix plays two distinct roles: First, as an incubator of novel zoonotic pathogens, and second, as a barrier to the transmission of those pathogens,” Chaves said. “We need to analyze the complex societal, political and ecological interactions that exist in particular agricultural matrices, which promote the conditions that create a barrier or minimize the conditions that create an incubator, to keep animal pathogens from jumping to humans to create new epidemics and pandemics.”

For example, they refer to previous research that looked at the Ebola virus epidemic in west Africa in 2014, explaining that the virus went from an intermittent infection in isolated villages to a widescale epidemic that infected 28,000 and killed 11,000 in that region. They say farmers had transformed areas of the Guinean forest into plantations as demand for international palm oil increased, which drew more bat species to the area, increasing human-bat contact and promoting transmission.

Or, they said, consider malaria, which in Costa Rica is associated with the development of pineapple plantations and open-field mining operations. But in similar landscapes in Africa, where farmers introduced irrigated rice, malaria transmission didn’t increase despite an increase in mosquito numbers. The researchers said that positive social change within these African communities, like improved housing, kept mosquitoes out of contact with humans and reduced transmission.

“Local decisions are vital in disease transmission,” Chaves said. “We have to widen our scope to better understand the relationship between humans, nature and the emergence of diseases. It is key to our future.”

Other authors of the One Earth article are Gordon Fitch of the University of Massachusetts, Amherst; Zachary Hajian-Forooshani, Nicholas Medina, John Vandermeer and Alexa White of the University of Michigan Department of Ecology and Evolutionary Biology; Benjamin Iuliano of the University of Wisconsin-Madison; Kevin Li, Jonathan Morris, Iris S. Rivera-Salinas and Kimberly Williams-Guillén of the U-M School for Environment and Sustainability; Beatriz Otero Jiménez of the University of Central Florida; and Chenyang Su of Dartmouth College.

Part of the study was conducted by Chaves while he was a scholar in the NIH Climate and Health Scholars Program. Chaves, Perfecto, Vandermeer and Li were partially funded by the U.S. National Science Foundation.