Deforestation reduces malaria bed nets’ effectiveness

When a forest is lost to development, some effects are obvious. Stumps and mud puddles across the landscape, a plowed field or houses a year after that. But deforestation isn’t just a loss of trees; it’s a loss of the countless benefits that forests provide—one of which is control of disease.

Now, a startling new global study shows that a widespread malaria-fighting strategy—bed nets—becomes less effective as deforestation rises. The research underscores how important a healthy environment can be for human health.

Insecticide-treated bed nets are one of the most common malaria prevention measures. They prevent malaria-transmitting mosquitos from biting residents as they sleep, and nonprofits distribute them widely, spending into the billions of dollars, said Gund Institute Director Taylor Ricketts.

The researchers found that bed-net use was associated with up to 32% lower malaria rates in children. However, bed-nets were only effective in areas where forests remained over 50% intact. The findings were published in People and Nature.

In other words, “bed-net use is effective in areas with lower deforestation rates, but when deforestation rate exceeds 50% over the 20-year period studied, bed-net use has no effect,” said lead author Tafesse Estifanos, a former postdoctoral scholar at UVM’s Gund Institute for Environment and still an affiliated scholar there.

“Tafesse’s research is a wake-up call for those working in public and planetary health. He has shown that the effectiveness of what we typically do to control malaria depends on the state of nature around the people we're trying to help,” Ricketts said. “I think in global public health, there is still a huge blind spot regarding the importance of nature.”

For the study, the researchers combined several types of information: demographic, health, and economic data about residents of the study area—combined with geographic and environmental data including deforestation, climate, and population density. They developed four categories of deforestation rate, ranging from nearly no forest loss to over 50% loss over the course of 20 years. The team also included data on bed-net use and malaria cases among children residing in the study areas.

Why does deforestation increase malaria risk? There are probably several interacting reasons, noted Ricketts, but one of them is that deforestation creates ideal habitat for malaria-carrying mosquitoes, leaving puddles of sun-warmed water in which the insects breed and thrive. The researchers next plan to look for the exact mechanism through which forest loss changes bed-net efficacy, Ricketts added.

This work builds from an earlier study, in which researchers showed that deforestation increases risk of malarial infection in children across six countries, especially for those in low-income communities.

“We have lots of case studies that look at the adoption and efficacy of malaria prevention, especially bed net access and use,” noted study coauthor and Rubenstein School of Environment professor Brendan Fisher. “What we were able to do here is get data on close to 20,000 children in six malaria-endemic countries to test, on a large scale, how natural and human mechanisms for malaria prevention interact."

The take-home message, said Estifanos and Ricketts, is that maintaining intact forests is not just a conservation goal—it’s a public health measure. “Especially in developing countries, where the resources are scarce and poverty is a significant factor, conservation of the environment has a dual purpose,” Estifanos said.

It also means that government and NGO efforts to improve public health—and the money spent on these efforts—can be wasted if deforestation overwhelms their effectiveness, Ricketts said. “If we don’t treat nature well, we could undermine the impressive gains we’ve made in public health.”

“By conserving the environment, we can help public health policy interventions,” Estifanos said. “Our project examines how poverty and environmental conservation interact in malaria transmission, and shows that environmental conservation has public health benefits.”

World Health Organization data reports over 600,000 deaths worldwide from malaria in 2022, nearly all of which occurred in Africa. Children are particularly vulnerable: over 75% of these malaria deaths were children.

Learn about UVM’s Planetary Health Initiative, which explores connections between nature and human health so that people and planet can thrive.