Bats have unusually proactive immune systems, which have a nasty habit of crafting viral strains that are hugely infectious and often deadly, as they’re essentially trained up while incubating in the bat’s body. They’re known carriers of the two coronaviruses SARS and MERS and are the most likely source of the current SARS-CoV-2 currently sweeping the globe. However, it’s thought that the COVID-19 coronavirus had to pass through a “middle man” before spreading to humans. A paper published in the journal Nature has identified closely related coronaviruses of the pandemic strain in pangolins. Although the research doesn't suggest pangolins are directly involved in the spread of the current outbreak, it does show them to be capable of hosting coronaviruses, and thus their trafficking and consumption should be halted to minimize the risk of potential future transmission.
Pangolins, or scaly anteaters, are mammals of the order Pholidota. These amazing armored creatures are covered in protective keratin scales and are the only known mammals to have them. Unfortunately, this unusual defensive feature has put them in harm’s way as their meat and scales have become highly sought-after ingredients for Chinese traditional medicine. Pangolin products are wrongly believed to cure a host of ailments including anxiety and hysterical crying in children, women “possessed” by devils and ogres, malarial fever and deafness. They are the most trafficked mammals in the world.
In order to better understand the devastating SARS-CoV-2 pathogen, a search is underway to identify the “missing link” species that facilitated the transmission of this specific coronavirus from bats to humans. Owing to their unique immune systems, bats are a common reservoir host where a pathogen can develop before passing onto another animal. The outbreak of COVID-19 has been linked to a wet market in China that had a vast array of animal products on sale, meaning there’s a lot to choose from in identifying the next step of spread. The search was made even more difficult as the market was cleared out shortly after news of the outbreak broke, preventing researchers from examining the specimens that were present at the time.
As one of the most commonly illegally trafficked animals in the world, it’s likely pangolins made up a proportion of the market’s stock. In light of this, a team of researchers from the University of Hong Kong investigated a small number of Malayan pangolins seized in anti-smuggling raids in China and discovered they were carriers of two close cousins of the SARS-CoV-2 coronavirus.
They sampled 18 animals from a shipment in southern China seized between August 2017 and January 2018 and found SARS-CoV-2 related coronaviruses in five of them. Out of a further 12 pangolins seized in a second province in 2018, three more carriers were found and there was a further carrier detected from a shipment in a third province in 2019.
The coronaviruses isolated from the carriers were found to have a sequence similarity of around 85-92 percent to SARS-CoV-2, with one virus showing a particularly strong similarity with a region that encodes for the “spike” protein, which is a defining feature of coronaviruses. The findings, however, aren’t concrete, as all detected strains were missing a sequential alteration that has been observed in the human SARS-CoV-2 pathogen. This throws into question how likely it is they could’ve passed the virus onto humans, although to date pangolins are the only mammals other than bats that have been found to be infected with a SARS-CoV-2 related pathogen.
The evidence isn’t sufficient to directly implicate pangolins in the outbreak of SARS-CoV-2, but the authors warn that captive pangolins should be handled with caution while further investigation is carried out as to their potential to infect humans. They also stress that their sale in wildlife markets should be halted immediately to prevent future outbreaks of this nature, a decision which has fortunately been supported by the Chinese government’s decision to ban the trade and consumption of wild animals in response to the pandemic.