Land use changes could increase risk of disease outbreaks

Aug. 5 (UPI) -- When land use changes disrupt ecosystems, new research suggests species known to carry diseases that infect humans benefit from the disruptions.

The findings, published Wednesday in the journal Nature, suggest land use changes caused by urbanization, agricultural expansion and other types of human activity could put humans at greater risk of infectious disease outbreaks.

For the new study, scientists analyzed data from 184 studies on 7,000 species, including 376 known to carry disease capable of infecting humans.

"One of the main challenges for these datasets are that they are from very different habitats and from a large number of separate studies that use contrasting methods to assess the types and numbers of animal species at each of our study sites," study co-author David Redding told UPI.

"Not only this, but the confidence that we can tell if a species is known to carry disease-causing pathogens, strongly depends on how much we have studied that particular species," said Redding, a researcher at the University College London's Center for Biodiversity.

To account for these biases, researchers used a complex statistical method known as linear mixed regression modeling.

"We have also had to run these analyses many times, slightly changing the data each time to ensure that any assumptions we made using these analyses did not adversely affect the results," Redding said.

Their analysis showed that as habitats are degraded, species that carry zoonotic diseases fare better than those that don't, either persisting or increasing in abundance.

"What this means is that animal communities in more human-dominated landscapes end up with a higher proportion of disease-carrying species, both in terms of species richness and in the total number of individuals," Redding said.

Scientists don't yet have an explanation for the phenomenon, but Redding suggests it's possible the species that do well in degraded and fragmented landscapes have invested in strong immune systems, allowing them to carry greater numbers of pathogens.

Researchers considered the possibility that species that either persist or thrive in human-dominated landscapes might simply have more opportunities to pass along pathogens to humans, while animals that don't may never get their chance to demonstrate their potential as carriers of zoonotic diseases.

"This was a key concern when we designed the study," Redding said.

"What our results show is that there is the same pattern with non-human infecting pathogens, Redding said. "Whereas if the results we see were mainly driven by ongoing human contact, we would expect non-human infecting pathogens to show some different relationship with land use change."

The findings add to the growing body of evidence that global land use changes are causing significant ecological damage, as well as fueling climate change -- and in turn, increasing the risks to human health.

The authors of the new study suggest land-management policy must account for the costs associated with land use changes.

"We need to do further work to understand how we can best design landscapes to prevent future disease risk," Redding said. "It might be that we need to share land with more intact ecological communities that are natural biological controls for disease-carrying species, such as predators."