Analysis of Coronavirus Spillover Risk in Southeast Asia
In a thorough analysis of previously published and new data, EcoHealth Alliance scientists seek to identify where future SARS-related coronavirus outbreaks are most likely to originate. The findings show that a high risk of SARSr-CoV spillover from bats to people extends from southern China throughout Southeast Asia, a geographically large and densely populated area where small outbreaks could spread quickly.
Relative risk of coronavirus spillover is mapped throughout southern China and Southeast Asia from lowest (purple) to highest (yellow)
The analysis involved producing the most realistic maps of the likely sites where bats known to carry coronaviruses live. These were coupled with population density estimates and measures of land use change to provide the most accurate estimates to date of where people and bats that carry SARS-related CoVs overlap.
The study, which has been submitted for peer review and is out now as a preprint, also built on previous EcoHealth Alliance research which found evidence of coronavirus spillover among people living near or in frequent interaction with bat roosting sites in China. In a study sampling 218 people, just under 3% tested positive for bat SARS-related CoV antibodies. Using this and other published data as a baseline to look at the potential for spillover throughout the hotspot region, the paper estimates that an average of 400,000 people per year are likely infected with bat-origin coronaviruses related to SARS-CoV and SARS-CoV-2 in southern China and Southeast Asia alone.
This research is done to help pinpoint areas for better surveillance, not just of the early warning signs of an outbreak, but also of potentially high-risk behavior like visiting bat caves or hunting and eating wildlife.
Bats are very common mammals and play a vital role in most ecological systems around the world. They come into frequent contact, not just with humans, but with other wild and domestic animals presenting ample opportunity for viral spillover. The best way to prevent outbreaks and pandemics is to prevent that initial spillover and to equip medical systems and clinicians in high-risk hotspot areas to recognize cases and control outbreaks before they get out of hand.
Bats are mostly nocturnal and aren’t frequently seen by humans. Exposure to viruses they carry can come from the contamination of food or surfaces with bat excrement or urine, by living near or sheltering in caves where bats roost, through the hunting, butchering, trade, and consumption of bats or other wildlife, and other close contact with bats and their waste, such as the collection of bat guano for use as fertilizer without appropriate safety measures or PPE.
Information gaps also present problems in preventing spillover. There are relatively few data mapping extensive wildlife farms and trade networks throughout the region, making it difficult to track the movement of potential secondary hosts. It is known that 14 million people worked in the wildlife trade in China as recently as 2016 and that each of these people come into regular contact with animals and this is likely to increase the overall risk of spillover and spread. Many of these farmed animals have the capacity to be infected by SARS-related CoVs, and they are rarely tested for viral infection.
Analyses like this allow the scientific community to more finely tune research and intervention measures so that they target areas and activities most likely to experience spillover of novel coronaviruses. Increased surveillance and community engagement can help to lessen this risk. By targeting the identified hotspots, we stand a better chance of disrupting the chain of spillover upstream.