Zoonotic viruses: Protect bats to protect people

South Africa’s bats are fast losing the trees that provide them with food, places to roost and landmarks to help them navigate. And the destruction of their habitat has implications for humans: the spread of potentially zoonotic viruses.

In a new study, Mariette Pretorius, a postdoctoral researcher at the University of Pretoria’s Centre for Viral Zoonoses and the Mammal Research Institute, describes how the removal of the country’s trees, harvested for timber products and firewood and cleared for agriculture and housing, is bringing wild animals such as bats into closer contact with humans than ever before.

In addition to the effects of tree loss, agricultural and urban intensification exposes bats to pesticides and other pollutants. 

“These impacts may have far-reaching consequences for bat health and survival,” says Pretorius. “In an era where land cover change increases pandemic likelihood, our research is an important step towards the formal protection of bat-inhabited caves to safeguard both bats and humans.”

Bats, along with domesticated species, primates and rodents, are a large and diverse order that host a variety of viruses with zoonotic potential, with several bat species in South Africa earmarked for ongoing monitoring for potentially zoonotic viruses.

At least 18% of South Africa’s 60 reported bat species are either fully or partially dependent on caves, yet caves and cave-dwelling bats are under-represented in conservation plans. 

In South Africa, at least two species that live in caves are of interest as transmission hosts for potential zoonotic viruses, specifically, various coronaviruses: the Natal long-fingered bat and the Egyptian fruit bat. 

Both species are numerous and widespread throughout the country.

“Land-use changes and urban expansions are a rising concern for both conservation and increased bat-human contact,” the study says, adding that these species are characterised by large population sizes and may often be found co-roosting, which increases the chance of cross-species viral sharing and infection. 

“The viral host status and the abundance of these two species throughout South Africa raises concerns about an increased chance for contact with humans and livestock. Concurrently, the lack of formal protection for these bats and their obligate roost environment is worrisome for continued cave-dwelling bat survival.” 

Pretorius investigated some of the human-caused pressures these species face around their caves. She used land-cover datasets from the former department of environmental affairs to determine the extent of land-cover change within 5km around 47 bat-inhabited caves between 2014 and 2018. 

The results showed an overall 4% decrease in trees around all caves, while agricultural and urban areas increased by 2.13% and 0.96% respectively. And distances between settlements and bat roosts have decreased.

Because many roosts are not located in well-protected ecosystems and no formal cave-conservation plans exist, important bat roost sites are at risk of human interference and destruction and the likelihood of bat-human contact throughout South Africa is increasing. “These developments are concerning for both human health and continued bat survival and cave-specific conservation is urgently required.”

Land cover around bat-inhabited caves in South Africa has changed and is continuing to change. “Within 5km of known cave roosts for these species throughout the country, agriculture, plantations and urban settlements have increased. Simultaneously, natural woody vegetation has declined around all roosts from 2014 to 2018.” 

South Africa has a rich assemblage of karst caves — shaped largely by water on limestone, dolomite and marble, resulting in surface and underground features such as gorges, caves and other underground openings — but much of the focus falls primarily on their archaeological and palaeontological significance. 

If no steps are taken to formally safeguard cave roost sites in South Africa, natural habitat loss, along with human intrusion at roost sites, will probably lead to more frequent human-bat encounters, increasing “the risk of zoonotic virus transmission from bats to humans”, according to the study.