Another way to prevent disease: Don’t mess with Mother Nature

A bat hangs from a tree branch.

The loss of winter food in the wild can drive bats into closer contact with humans. (Photo by Chris Hudson.)

Trees along the Nanay River in the Peruvian rainforest fell as the population exploded, a road was paved and fields expanded. Researchers, including Jonathan Patz, director of the University of Wisconsin-Madison Global Health Institute (GHI), showed the rate of bites from malaria-carrying mosquitoes was more than 200 times higher than in forested areas.

Diseases emerge as forests are leveled to make way for agriculture and heavily-populated cities. Researchers, including Raina Plowright, an associate professor at Montana State University, found that the loss of winter food can drive Australian bats into closer contact with humans in agricultural and urban areas, where researchers see an emergence of the deadly Hendra virus.

Today (March 5) in The Lancet Planetary Health, Patz and Plowright join colleagues from across disciplines in calling for a deeper and broader look at how changes to the landscape—from deforestation to climate change—influence diseases, animal biology and human-animal interactions.

“Land use-induced spillover: A call to action to safeguard environmental, animal, and human health” looks for collaboration among environmental, wildlife and human health researchers and practitioners to understand the roots of zoonotic diseases—those spread from animals to humans—like COVID-19, Ebola and AIDS.

The paper, with authors from universities and conservation organizations across North America, is based on the premise that science can identify and foster healthy ecosystems and reduce the risk of zoonotic spillover. “Human health is a return on investment for protecting the landscapes, ecosystems and wildlife,” Plowright says. “If we want to stop pandemics, we should prescribe nature.”

Disease prevention is a top priority, says Patz, also a professor in the Nelson Institute for Environmental Studies and Department of Population Health Sciences. While he acknowledges the need for early surveillance to detect the outbreaks of diseases like COVID-19, this paper looks at addressing why diseases move from animals into human populations. “We have an opportunity for even earlier prevention by broadening our focus to include relationships between environmental disruption and disease dynamics even before the first human is infected,” he says.

“Protecting nature is critical for preventing the spillover of pathogens from wildlife to humans,” says co-author Gary Tabor, president of the Center for Large Landscape Conservation in Montana and a member of the GHI Board of Visitors. “As most emerging infectious diseases come from wildlife, and many of these diseases have epidemic or pandemic potential, public health strategies must also consider nature-based solutions to disease prevention.”

A graphic shows the infect-shed-spill-spread cycle.
The disease cycle can bring disease from animals to humans.

Interrupting the infect-shed-spill-spread cycle

The paper is built on the infect-shed-spill-spread cycle of disease, a concept that’s become familiar as scientists try to trace the origin and outcomes of diseases including COVID-19.

  • Infect looks at how and why animals are infected and the dynamics of the infection, including how much disease is present, where and when.
  • Shed is when the infected animals release pathogens into the environment in a variety of ways, from breathing to being slaughtered.
  • Spill marks the passage, or “spillover,” of the disease from animal to human, becoming a zoonotic infection.
  • Spread is the human-to-human transmission.

“The risk of a person getting infected with a pathogen from wildlife depends where wild animals are infected, how much infection they carry and how much pathogen is released from these wildlife hosts,” Plowright says. “Environmental destruction can amplify each of these factors and then also bring humans into contact with the infected animals, triggering the start of a pandemic. If we can stop the conditions that lead to high levels of infection in wildlife, and human contact with wildlife, we can prevent pandemics before they happen.”

Fostering landscape immunity

The scientists believe new research will quantify what they call “landscape immunity,” or creating environmental conditions that support healthy wildlife and biodiversity with the resulting benefits for human health. They look toward a land management philosophy to minimize the emergence of zoonotic diseases like COVID-19.

“Much of our understanding of the “don’t mess with nature” concept has been anecdotal,” Tabor says. “But we show how intact ecosystems provide a degree of ‘landscape immunity’ to disease spread to people.”

The paper also shows again how human, animal and ecosystem health are intertwined and the need for interdisciplinary approaches to global health.

“The overwhelming number of lives lost to COVID and the resulting economic consequences of this pandemic have, sadly, revealed the weaknesses in both our public health and nature conservation infrastructures,” Tabor says. “Organizations such as GHI were designed to marshal the broad skill sets of the university to tackle this grand challenge that is affecting all life on the planet including our own.”

By Ann Grauvogl/ March 5, 2021