The Pangolin’s Revenge - Owen Epstein

Wuhan is the capital city of Hubei province in the People’s Republic of China. An ancient city, first settled 3,500 years ago, Wuhan is currently home to eleven million inhabitants serving as a major regional rail and road hub and home to outstanding universities, high tech science parks and factories.

Hidden within Wuhan’s dynamic urban landscape lurks the “Huanan Seafood Market”. The market is dubbed “wet” as opposed to “dry” as its traders deal in perishable staples and exotic delicacies rather than durables such as clothing and electrical goods. In addition to trading fish, the market offers a wide selection of domesticated and wild birds and animals for consumption. There are no refrigerated cabinets with neat packages of meat and fish stamped with a “use by” date. Rather a cacophonous gathering of shoppers, squeezed together with live and slaughtered animals in narrow lanes and crowded stalls with sodden floors stained with the remnants of recent street-side slaughter. Although designated a seafood market, the market traded a menagerie of exotic wild animals including civets, beavers, crocodiles, dogs, foxes, pangolins, peacocks, porcupines and turtles.

As 2019 turned to 2020, almost all mankind turned their thoughts to this previously unknown city and its Seafood Market. Reports emerged of a cluster of local inhabitants requiring intensive hospital care for severe pneumonia. Most, although not all, had recently shopped in the market. By the 2nd of January, the Chinese scientists tasked with identifying the cause of the outbreak announced that the infectious agent was a coronavirus never encountered in humans. Like all viruses, this interloper required nomenclature, and in line with its phylogeny, was classified as SARS -CoV-2 (commonly termed Covid-19).

The announcement brought a shudder to virologists, epidemiologists and healthcare professionals reminded of previous zoonotics, Zoonosis is the term used to describe animal diseases, like rabies, that can be transmitted from animals to humans. The newly identified animal coronavirus had made a sudden jump to infect humans. The link between exotic meat, newly described viruses and human disease is seared into recent memory. In 2002, an outbreak of a contagious epidemic pneumonia (SARS) was traced to a novel coronavirus that had skipped from bats to civet cats bred for human consumption. In 2012, an outbreak of severe pneumonia in Saudi Arabia (MERS) was traced to another novel coronavirus strain that had made a species jump, almost certainly from camels to humans.

The spread of SARS was quickly contained as most patients developed severe viral pneumonia allowing rapid recognition, isolation and contact tracing. It was soon evident that the highly contagious SARS-CoV-2, expressed a different personality, with a minority of infected individuals displaying symptoms severe enough to seek medical attention. Like an iceberg, the bulk of infection lay unsuspected in the depths of the afflicted population creating an ideal medium for the virus to propagate and then disseminate across borders and into the wider world.

What was the trail from the exotic meats in the Wuhan market and the sudden jump to humans? Which exotic animal in the market had hosted the SARS-Cov-2? The horseshoe bat was quickly incriminated as the most likely primary host, but bats were not traded in the market. Most likely was transmission from bat to human via an innocent intermediate host, almost certainly an exotic animal caged for slaughter in the market. Snakes were the first to feature in the identity parade. Genetic analysis of the market’s snake population suggested that snake cells might provide a hospitable landing zone for the bat coronavirus. However, this proposition is unlikely as there is no precedent for a coronavirus jumping from a cold-blooded to a warm-blooded animal.

Enter the market’s current chief suspect, the highly prized pangolin. This scaly ant eating mammal hosts its own coronavirus, and a strain endemic to Malayan pangolins, shares 91% of its genetic sequence with a SARS-CoV-2 virus isolated from horseshoe bats. In particular, the bat and pangolin coronavirus share a striking molecular similarity of the characteristic spike proteins that locks the virus to the animal cell prior to penetration. It seemed reasonable to propose that the genetic similarities of the bat and pangolin coronaviruses facilitated transmission from bat to pangolin and via a second jump, from pangolin to humans. The pangolin hypothesis remains controversial and is yet to be proven, but amongst all the potential intermediate hosts in the market, this strange and lonesome mammal of the African and Asian landscape remains a likely conduit for an ancestral bat coronavirus to have jumped to humans.

Who would choose to eat a pangolin? Cultural superstition has endowed this rare and harmless mammal with magical medicinal and aphrodisiac properties. Ruthless poaching places all pangolin species at the extreme limit of extinction. Has the pangolin reaped its revenge?