The pangolin, a mammal distinguished by its unique scale armor, became a figure in global health discussions. As scientists sought the origins of a novel coronavirus, their inquiry turned to the animal kingdom. The pangolin was identified as a potential source, launching an investigation into its connection with the virus that causes COVID-19.
The Basis for Suspecting Pangolins
The investigation into SARS-CoV-2 origins introduced the term zoonotic disease, an illness that jumps from an animal to a human. Scientists focused on identifying an “intermediate host,” an animal that could have contracted the virus from its natural source and passed it to people.
Pangolins became a subject of this search because they are frequently and illegally trafficked, creating opportunities for viral transmission to humans under unhygienic conditions. This suspicion was amplified by the discovery of pangolins in the Huanan Seafood Wholesale Market in Wuhan, a location linked to the initial outbreak. Researchers also knew that pangolins could harbor their own coronaviruses, creating a strong circumstantial case for their involvement.
Analyzing the Genetic Evidence
The scientific case for a pangolin link intensified with early genetic analysis. Scientists sequencing the genome of a coronavirus from smuggled Malayan pangolins found the Receptor-Binding Domain (RBD) of its spike protein was very similar to that of SARS-CoV-2. The RBD acts like a key, allowing the virus to enter host cells by binding to the ACE2 receptor on human cells. This near-identical match in the RBD initially suggested a direct evolutionary link.
The finding was significant because the equivalent RBD in the closest known bat coronavirus, RaTG13, was less similar to the human virus. This led to a hypothesis that the unique RBD of SARS-CoV-2 might have evolved in pangolins. However, a comprehensive look at the genetic data revealed a different story. While the RBD “key” was a match, the overall genetic backbone of the pangolin coronavirus was substantially different from SARS-CoV-2, sharing only about 90-92% of its genetic material and indicating it could not be the direct ancestor.
The Current Scientific Consensus
The investigation has since broadened, with bats now widely considered the most probable natural reservoir for SARS-CoV-2. This is based on the discovery of the bat coronavirus RaTG13, which shares approximately 96% of its overall genome with SARS-CoV-2, a much closer match than any pangolin-derived coronavirus. This genetic similarity points toward a bat origin, even though the RBD of RaTG13 is less similar to the human virus than the pangolin version is.
This evidence led to a revised understanding of the pangolin’s role, with the scientific view being that they are not the direct intermediate host. Instead, the origin story is likely more intricate, possibly involving a process called recombination where a bat and pangolin coronavirus infected the same animal. It is also conceivable that another unidentified animal served as the true intermediate host.
While coronaviruses have been identified in pangolins, the direct lineage to humans is not supported by the full body of genetic evidence. The search continues, acknowledging the complexities of viral evolution.
Implications for Public Health and Pangolin Conservation
The investigation into the pangolin-coronavirus link, despite not confirming a direct connection, has provided lessons for public health. It highlighted the dangers posed by the illegal wildlife trade and live animal markets. These environments, where various species are kept in close and unsanitary confinement, create an ideal setting for viruses to jump between animals and to humans, a process known as zoonotic spillover. The pangolin case serves as a global warning about how these practices can create pathways for new infectious diseases to emerge.
Simultaneously, the media and scientific focus had a profound impact on pangolin conservation. As the pangolin became a household name, global awareness of its plight as the world’s most trafficked mammal increased. This attention has invigorated conservation efforts, adding urgency to campaigns against poaching and the illegal trade networks. Protecting endangered species is not only a matter of biodiversity but also a measure for safeguarding human health.