While it is believed that the SARS-CoV-2 coronavirus may have originated in Wuhan, China, and in bats, the jury is still out on its exact source. In certain parts of the world, the conditions of interaction between potential animal hosts and humans are a perfect recipe for disaster. Therefore, knowing such viral hotbeds may help prevent pandemics such as COVID-19 in the future. Taking a step in that direction, a new study has identified 'hotspots' where new coronaviruses may emerge from.

An international team of scientists used remote analysis tools to examine land-use patterns and distribution of Asian horseshoe bats—the species of bat that harbors several coronaviruses related to severe acute respiratory syndrome (SARS)—and identified potential 'hotspots' where the zoonotic viruses from the species could potentially jump to humans. According to the study, most of the current hotspots are clustered in China, and several regions in other countries heading towards becoming new hotspots. The study also identified hotspots in India. 

"Human health is intertwined with environmental health and also animal health. Our study is one of the first to connect the dots and really drill down into the geographic data on land use to see how humans are coming into contact with species that might be carriers," said Dr. Paolo D'Odorico, co-author of the study, in a statement.

Land Use and Spillover of Viruses

Horseshoe Bat
Rhinolophus lepidus (Representational Picture)Wikimedia Commons/David Raju

The final scene from the Hollywood 'pandemic thriller'Contagion is frighteningly real. It highlights how aggressive forest fragmentation and land use by humans may lead to unexpected and hazardous interactions between multiple species that can result in unfavorable outcomes. Researchers believe that the SARS-CoV-2 likely emerged from horseshoe bats and jumped to humans possibly through an intermediate host (the pangolin). And this transmission may have potentially arisen due to land use-led contact.

"Land use changes can have an important impact on human health, both because we are modifying the environment, but also because they can increase our exposure to zoonotic disease," emphasized Dr. Paolo D'Odorico, co-author of the study. The concurrence of three factors— fragmentation, livestock density and human settlement—made for a hotspot according to the authors. 

For the study, the authors analyzed comprehensive and high-resolution datasets on forest cover, livestock density, cropland distribution, human settlements, human population, land-use changes, and distribution of Asian horseshoe bats, in the areas populated by the bat species. Approximately, 28.5 million sq km forms the natural range of horseshoe bats.

Hotspots Across Several Countries

The hotspot analysis is based on the average G∗i z score values for fragmentation, livestock (cattle, goats, pigs, sheep) density, and human settlements. Hotspots are classified based on their two-tailed significance levels, corresponding to those of a standard normal distribution.Rulli, M.C., D'Odorico, P., Galli, N. et al. / Nature

Analysis of the data revealed that most of the current hotspots are concentrated in China. According to the team, this clustering is a consequence of the growing demand for meat products which has impelled the proliferation of industrial livestock farming on a massive scale. They also noted that the danger presented by concentrated livestock production is specifically enormous as large populations of genetically similar animals are brought together by the practice. More than often, several of these animals are immune-suppressed and extremely vulnerable to outbreaks of infections and diseases, the authors added. 

However, the hotspots were found not to be confined to China alone. Other prime global hotspots were found to be located in Bhutan, east Nepal, northern Bangladesh, Java, northeast India, and the Indian state of Kerala. Interestingly, regions in Bangladesh and northeast India have experienced past outbreaks of another bat-related zoonotic disease—the Nipah virus. Through their investigation, the scientists learnt that other parts of Asia were at the risk of becoming hotspots of coronavirus spillovers due to increasing forest fragmentation. These regions are situated in Japan, the northern Philippines, and China (particularly south of Shangai).

In addition to this, the analysis also found that parts of Thailand may eventually become hotspots as livestock production in the areas increases. Dr. Maria Cristina Rulli, co-author of the study, remarked, " We hope these results could be useful for identifying region-specific targeted interventions needed to increase resilience to coronavirus spillovers."

Creation of Hotspots

Clearing Land
Clearing forests (Representational Picture)Pixabay

When the natural habitats of wildlife are encroached upon by humans, it indirectly leads to an increased risk of exposure to zoonotic disease by decreasing vital biodiversity. Certain species require specific habitats to survive and are called 'specialists'. Some species can thrive in any habitat and are called 'generalists'. When forests undergo fragmentation and destruction of natural habitats occurs, 'specialists' begin dying out. This lack of competition helps 'generalist' species take over and flourish.

Being a 'generalist', horseshoe bats are often found in areas marked by human disturbance. A previous study by some of the current team members had found a connection between habitat destruction and fragmentation of forests in Africa, and the outbreaks of the deadly Ebola virus.

"By creating conditions that are disadvantageous to specialist species, generalist species are able to thrive. While we are unable to directly trace the transmission of SARS-CoV-2 from wildlife to humans, we do know that the type of land-use change that brings humans into the picture is typically associated with the presence of these bats who are known to carry the virus," stated Dr. D'Odorico.