Habitat destruction could fuel disease risk

Scientists have been sounding progressively louder alarms about the repercussions of human expansion across the planet through intensive agriculture, deforestation and urbanisation, destroying wildlife habitats in the process.

These activities don’t just impact biodiversity, ecosystems and livelihoods. They could also help foster the growth of animals that carry diseases known to infect humans, according to a study published in the journal Nature.

“The way humans change landscapes across the world, from natural forest to farmland, for example, has consistent impacts on many wild animal species,” says first author Rory Gibb from University College London, UK.

“Our findings show that the animals that remain in more human dominated environments are those that are more likely to carry infectious diseases that can make people sick.”

The authors suggest animals more likely to survive in human-dominated landscapes may have biological or ecological traits that are related to greater zoonotic disease carrying capacity.

Zoonoses are human diseases caused by pathogens such as bacteria, viruses, protists and worms that are naturally carried by animals and can “spillover” to people.

Potential links between risk of zoonoses, which include Lyme disease, West Nile fever, Chagas disease and malaria, and biodiversity loss have been a topic of debate amongst scientists, with conflicting views and findings.

Much of the research has focussed on specific diseases in specific areas, Gibb explains, and global studies have been limited by poor or limited data.

His team accessed a dataset, PREDICTS, that includes site-level species data from 184 studies collected across a gradient of undisturbed to disturbed landscapes in thousands of sites across six continents, and cross-checked them with records of 376 zoonotic disease-carrying species.

As human land use intensified, they found ecological communities were increasingly and predictably dominated by disease carrying species, by either persisting or multiplying while the overall community of species declines.

This trend was most pronounced for rodent, bat and passerine bird species that carry zoonotic diseases, which may account for their emergence as important hosts.

Although evidence suggests COVID-19 most likely somehow originated from bats, the study doesn’t shed specific light on links between land use and the current pandemic, says Gibb.

Rather, it gives “insights in the general, global context of human-driven biodiversity changes that make the spillover and emergence of known and novel zoonoses more likely”.

Intensive livestock breeding can also increase human exposure to pathogens as these farm animals have increased exposure to wildlife and can act as intermediate hosts, Gibb says.

He notes that while their findings highlight a risk for zoonotic spillover in human-dominated landscapes, several other elements come into play for disease to spread.

These include socioeconomic factors such as livelihoods, hygiene, access to water and sanitation and affordable healthcare, which need special attention in areas of intensive land disturbance – scenarios that commonly overlap in low- and middle-income countries where rich nations are driving deforestation and intensive agriculture.