Habitat destruction makes another Covid-19 'entirely feasible' - NZ scientist

The study explored human populations and livestock densities near bat locations - specifically greater horseshoe bats - around China and nearby regions. Photo / 123RF

A New Zealand scientist who's just explored the likely roots of Covid-19 says it's "entirely feasible" the world will see more pandemics as long as humans keep destroying natural habitats.

Because Sars-coronaviruses come from wildlife - and probably relatively recently from bats - it's widely assumed the global Covid-19 crisis had its roots in increasing interactions between humans and nature.

So far, there haven't been any quantitative analyses to back this up, said Massey University's Professor David Hayman, one of the world's leading experts in infectious disease ecology.

But there was more than enough evidence from other notorious diseases to show how growing human encroachment into habitats raised the risk.

In Africa, for instance, Hayman and colleagues have carried out studies drawing a direct link between tropical forest fragmentation and outbreaks of the much-feared Ebola virus disease.

"The question was whether we could see if there were similar human driven processes like forest fragmentation and farming that could have increased the risk of this outbreak and if China had been and is at particular risk," he said.

While New Zealand was under lockdown, Hayman and fellow researchers from the University of California and Italy's Polytechnic University of Milan began looking for an answer.

"The study involved me searching for data of locations where the bats which are hosts to Sars-related viruses had been recorded in China, as well as where the same species exist outside the country but in the region."

At the same time, his colleague, Associate Professor Cristina Rulli, analysed satellite data of the earth's surface.

"Then, when we had the bat location data we tested whether there were recent changes in those localities in forest cover, human and domestic animal density and where the high risk locations were."

The team discovered many parts of China with high human populations and densities of livestock, along with many areas of fragmented forest.

There's increasing evidence that our activities such as clearing forests is increasing the chances of new disease outbreaks, says Massey University's Professor David Hayman. Photo / Supplied

That made them "hotspots" for livestock and people to have contact with wildlife, and in particular, the bats that host Sars-related viruses.

"Interestingly, we also discovered some areas that were at risk of transitioning to become high-risk locations," Hayman said.

"We identified what changes might cause that, for example, the Chinese region south of Shanghai can potentially turn into a hotspot with increasing forest fragmentation, as can parts of Japan and northern Philippines."

Hayman said the study - just released as a pre-print, or before peer review - further highlighted how habitat destruction can heighten risk of outbreaks.

Earlier this year, University of California scientists looked at 142 known viruses known to "spill over" from animals to humans, along with species that have been implicated as potential hosts.

That data revealed clear trends in spillover risk which showed how people had interacted with animals throughout history.

They found domesticated animals like livestock shared the highest number of viruses with humans, with eight times more "zoonotic" viruses compared to wild mammalian species – likely a result of man's centuries-long contact with them.

Wild animals that had increased in abundance and adapted well to human-dominated environments also shared more viruses with people.

These included some rodent, bat and primate species that live among people, near our homes, and around our farms and crops, making them high-risk for ongoing transmission of viruses to people.

At the other end of the spectrum were threatened and endangered species – or animals whose population declines were connected to hunting, wildlife trade and decreases in habitat quality.

These species were predicted to host twice as many zoonotic viruses compared to threatened species that had populations decreasing for other reasons.

Threatened and endangered species also tended to be highly managed and directly monitored by humans trying to bring about their population recovery, which further put them into greater contact with people.

Bats repeatedly have been implicated as a source of "high consequence" pathogens, including Sars, Nipah virus, Marburg virus and ebolaviruses.

Hayman said that, to date, nearly all emerging infectious diseases and particularly novel viruses - from HIV and Ebola to the Sars virus that causes Covid-19 - had stemmed from wildlife.

"There is increasing evidence that our activities such as clearing forest for logging or to replace them with towns and farms is not only bad for the environment, but is actually increasing the chances of new disease outbreaks," he said.

"We need to look at the drivers of those, like what we eat, how we farm and develop land, and start to better plan, because if we don't choose to conserve over convert or destroy it's entirely feasible there will be another pandemic of another virus."