Pangolins Study Shows Wildlife Trade Significantly Increases Risk of Pathogen Spillover

An oral swab is collected from a pangolin by WCS wildlife health professionals at a wildlife rescue center in Vietnam. Samples collected from pangolins confiscated from the illegal wildlife trade were screened for coronaviruses and other pathogens at Vietnamese research and diagnostic laboratories. Credit: WCS Vietnam

The authors of a recent study that detected SARS-CoV-2 related coronaviruses in illegally transported pangolins say more needs to be done regarding both legal and illegal wildlife trade if humans wish to avoid multiples and epidemics caused by zoonotic-origin pathogens in the future .

The research team, led by scientists from the Wildlife Conservation Society (WCS), tested samples from 246 pangolins from wildlife confiscation events that occurred in Vietnam between 2015 and 2018. Of these, seven individual pangolins tested positive for a SARS-CoV-2- related to coronavirus.

While the scientists did not perform full genome sequencing to characterize the pangolin CoVs, they did screen the samples using a standard PCR/qPCR approach. However, the researchers quickly discovered that neither of the two broadly reactive conventional PCR assays, nor the RT-PCR assay targeting the RNA-dependent RNA polymerase gene—including one specifically designed for SARS-CoV-2—were able to successfully detect pangolin CoVs .

Only the RT-PCR assay targeting the E gene (developed by Victor Corman and collaborators) and the team’s own PCR assay based on pangolin-CoV specific primers were able to amplify short sequences of pangolin CoVs.

The unexpected discovery forced the scientists to question previously published research by Lee et al. that seemingly showed pangolin samples collected in Malaysia were not infected by CoVs.

“Additional investigations using PCR primers specific to pangolin CoVs would therefore be needed to confirm these and other results,” the researchers write in their paper, published in Frontiers in Public Health. “In the interim, mitigation measures should consider that the wildlife trade spillover interface contains novel viruses, which may not be detectable with current diagnostic tests. These findings have important implications for further CoV surveillance efforts in pangolins and potentially other species.”

In addition to testing pangolins for SARS-CoV-2, the authors reviewed related media reports of pangolin coronavirus trafficking cases between 2016 and 2020. The main route for the illegal trade of Sunda pangolins in Southeast Asia has been documented as flowing along the Indonesia- Malaysia-Thailand-Lao-Vietnam-China route.

The Lee et. al paper found no evidence of CoVs in pangolins taken from Malaysia—the beginning of the illegal trade route. However, the current study examined samples from pangolins from Vietnam—the end of the trade route.

“Our study therefore provides a ‘midstream’ sampling point in the ‘upstream’ to ‘downstream’ pangolin supply chain described by Lee et al., and this contributes additional insight into the role of the expanding trade in wildlife as a risk factor for the emergence of novel zoonotic-origin pathogens like SARS-CoV-2,” the WCS team explains in their paper. “This progression in positivity rate and apparent amplification of risk of CoV infection aligns with Vietnam’s role as a major transit country in the trade of live pangolins and pangolin carcasses sourced from pangolin strongholds in other Southeast Asian countries.”

The researchers also found that multiple pangolin confiscation events, including the ones sampled for this study, involved other live wildlife, including a mix of non-human primates, reptiles and birds.

“The review…supports long held concerns that the wildlife trade, moving wildlife species out of their natural habitats and into human-dominated landscapes and large urban centers, poses a serious and increasing risk of initiating epidemics from emerging pathogens in human populations,” write the scientists.

While WHO, the United Nations Environmental Program and the International Organization for Animal Health have passed guidance and called on nationals to suspend the trade of live caught wild animals for food or breeding purposes, this international research team says these regulations are not enough. They believe the regulations are too narrowly focused on open markets, failing to address the much longer wildlife supply chains and trade of both legally and illegally sourced wildlife.

“Additional surveillance for viruses of pandemic potential along wildlife supply chains, and a more comprehensive understanding of the complexity of wildlife supply chains is needed to inform wildlife trade regulation policy,” concludes the team.

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