Bat-Borne Sarbecoviruses Spilled Over in Southeast Asia Pre-Pandemic

Elephant loggers bring in a timber harvest in Myanmar.
Photo Credit: Tierra Smiley Evans/UC Davis

Scientific Frontline: "At a Glance" Summary: Bat-Borne Sarbecoviruses Spilled Over in Southeast Asia Pre-Pandemic

• Main Discovery: A virus previously found exclusively in bats was detected in the antibodies of human populations in rural Myanmar, demonstrating that exposure to diverse sarbecoviruses, including strains closely related to SARS-CoV-2, occurred prior to the pandemic.
• Methodology: Researchers collaborated with local clinics to screen nearly 700 rural and urban residents for sarbecoviruses between July 2017 and February 2020. The surveillance relied entirely on human patient sampling, targeting individuals seeking medical treatment and healthy populations near elephant logging camps, without collecting direct wildlife samples.
• Key Data: Blood screenings revealed that 12 percent of the study participants possessed antibodies indicating past exposure to a sarbecovirus, though no active infections were found. Exposure was exclusively identified in rural residents, particularly those working in logging, hunting, or bat guano harvesting, which put them in direct proximity to bats.
• Significance: The results yield concrete epidemiologic and immunologic evidence that zoonotic spillover of bat-borne coronaviruses is actively occurring. The data strongly suggests that human intrusion into newly disturbed, biodiverse environments substantially elevates the risk of wildlife-to-human viral transmission.
• Future Application: The findings establish a baseline for developing targeted mitigation strategies and underscore the necessity of continuous viral surveillance at the human-wildlife interface in Southeast Asia. This reconnaissance approach will be utilized to predict and potentially intercept the future emergence of novel zoonotic diseases.
• Branch of Science: Virology, Epidemiology

A virus previously found only in bats was detected in the antibodies of people screened for exposure to sarbecoviruses between 2017 and 2020 in rural Myanmar in Southeast Asia, according to a study from the University of California, Davis and collaborators in Myanmar and Singapore. The work is published in the International Journal of Infectious Diseases.

Sarbecoviruses are a group of coronaviruses. This study found exposure to diverse sarbecoviruses, including some known to be closely related to SARS-CoV-2, such as RaTG13.

The study found that people were significantly more likely to have been exposed to sarbecoviruses if their livelihood involved working directly with or close to bats, such as logging, hunting or harvesting bat guano.

“This study provides new evidence that bat-borne coronaviruses can and do spill over to people, underscoring the importance of surveillance in high-risk rural areas, where humans and wildlife closely interact,” said lead author Tierra Smiley Evans, an epidemiologist and research faculty with the One Health Institute in the UC Davis School of Veterinary Medicine.

Reconnaissance work

Partnering with local clinics in Myanmar, the study’s scientists screened nearly 700 people for sarbecoviruses between July 2017 and February 2020, before the first reported case of SARS-CoV-2 in Myanmar. They did not detect any active infections. However, 12% of study participants had antibodies in their system indicating they had been exposed to a sarbecovirus in their past.

While both rural and urban residents were tested, only people from rural areas had been exposed, and most of them worked in forested areas and extractive industries, such as mining, logging or hunting. This suggests that newly disturbed, biodiverse environments can increase the risk of wildlife-to-human transmission of viruses.

No wildlife was sampled for the study. Instead, people seeking treatment for fever in rural and urban clinics were enrolled in the surveillance studies, as were patients from clinics near local elephant logging camps. In Myanmar, the traditional method of using elephants to harvest timber is still practiced, so a network of temporary logging villages dots the forest edges. Samples were also collected from healthy people living in regions believed to have high levels of contact with bats.

“It’s like reconnaissance work,” Smiley Evans said. “We get an idea of what’s in the forest by looking at what people have been exposed to, without even going into the forest.”

Evidence of spillover

The study provides epidemiologic and immunologic evidence that zoonotic spillover is occurring.

“Our findings underpin the critical importance of continued surveillance at the rural wildlife-human interface in Southeast Asia, where some of the highest levels of known mammalian diversity exist and where future emergence of zoonotic diseases is likely,” the study said.

Funding: The study was funded by the National Institutes of Health, National Institute of Allergy and Infectious Diseases, National Science Foundation, United States Agency for International Development, and the National Medical Research Council Singapore.

Funding newly awarded from the NIH will allow the scientists to further investigate behaviors that contribute to sarbecovirus spillover and strategies to mitigate exposure.

Published in journal: International Journal of Infectious Diseases

Title: Exposure to diverse sarbecoviruses indicates frequent zoonotic spillover in human communities interacting with wildlife

Authors: Tierra Smiley Evansa, Chee Wah Tanb, Ohnmar Aunga, Sabai Phyuc, Htin Lind, Lark L. Coffeye, Aung Than Toea, Pyaephyo Aung, Tin Htun Aung, Nyein Thu Aunga, Christopher M. Weisse,  Kyaw Zin Thantg, Zaw Than Htund, Suzan Murrayh, Linfa Wang, Christine Kreuder Johnsona, and Hlaing Myat Thu

Source/Credit: University of California, Davis | Kat Kerlin

Reference Number: vi060923_01

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