Changing landscapes alter ‘disease landscapes’: Study

A new study has highlighted how and when changes in the environment lead to transmissible animal disease thresholds being exceeded, allowing for a better understanding and increased ability to predict the risk of transmission.

For the first time, researchers from Griffith University, Stanford University and the University of California used cumulative pressure mapping and machine learning to better understand how six vector-borne diseases (those transmitted by the bite of insects) found in different environments respond to human impacts. pressures.

Posted in Sustainability of Naturethe research found that diseases associated with lower human pressure, including malaria, cutaneous leishmaniasis, and visceral leishmaniasis, gave way to diseases associated with high human pressure, such as dengue, chikungunya, and Zika.

The human impact on Earth

“Humans are very good at modifying the Earth—as much as 95% of the Earth’s surface has been modified in some way by humans,” said Dr Eloise Skinner, lead researcher of the study from Griffith’s Center for Planetary Health and Food Security .

“We know that when we modify the Earth’s surface we also change the species community, which includes plants, animals and insects.”

“What we didn’t know until recently is how these changes in species change disease risk in humans.”

Dr. Skinner said the findings enhance the ability to predict these transitions, and will support a dynamic public health care infrastructure that could adapt to changes in disease occurrence through space and time.

Vector-borne diseases are a global challenge

Vector-borne diseases (VBDs) are highly responsive to environmental changes, but such responses are notoriously difficult to isolate because pathogen transmission depends on a range of ecological and social responses to vectors and hosts that may differ between species.

With more than half of the world’s population at risk of contracting VBD, Dr. Skinner and team recognized how changes in the environment affected the unique transmission cycle of each disease presented various complexities.

“Often, vectors and pathogens occupy their own unique niche, so that each cycle of transmission clearly responds to environmental change,” he said.

“With increasing human pressure, one would expect transitions in the occurrence of different diseases – for example, dengue fever is a highly urban pathogen while malaria occurs at the frontier of deforestation.

“But how urban does an area have to be for dengue to become a risk? How much forest has to be converted before we start seeing increases in malaria?”

These are some of the research questions the team sought to answer, to highlight land-use transition thresholds that could lead to sharp shifts in infectious disease burden and public health needs.

Impact thresholds were identified, first

For the first time, researchers were able to identify distinct boundaries of human impact that specific diseases occupy.

Comparing six vector-borne diseases in Brazil, the team found that in a critical window in which the human footprint changed from moderate (4-7) to high (7-12) to severe (>12), disease occurrence shifted sharply from malaria, cutaneous leishmaniasis and visceral leishmaniasis to dengue fever, chikungunya and Zika (arboviruses transmitted by the urban mosquito Aedes aegypti).

“These are diseases that require distinct responses to vector control, diagnosis and environmental management,” Dr. Skinner said.

“Because biomedical and chemical approaches alone have failed to sustainably eradicate these diseases, managing the socio-ecological contexts that promote pathogen transmission is a critical frontier for global health.”

“Combined with climate pressures, human pressure is a significant risk of disease occurrence and transmission and therefore a major threat to human and environmental well-being.”

“Brazil was an ideal case study to assess the human pressure on disease transmission because it is a large, ecologically and socioeconomically diverse country that contains many biogeographic zones, intense and variable land-use pressures, a high incidence of multiple diseases with contrasting ecologies, and a long-standing national disease surveillance system’.