Friday, May 29-Monday, June 1, 2020
Speculation about the origin of the newest coronavirus circulates around pangolins, laboratories, a wet animal market in Wuhan, viral mutations and bats. I just had to put on my biologist hat this weekend and see if a little research might help to connect the dots. SARS-CoV-2 is the third animal coronavirus to burst into the human world in the twenty-first century. Chances are it’s not the last. And what is a pangolin, anyway?
It all begins with a virus. Viruses are little bundles of genetic material, RNA or DNA, wrapped up in a protein coat. They replicate by inserting their genetic material into a living cell and using that cell’s DNA to produce more viruses. Viruses can infect bacteria, plants, and animals, including humans. Viruses have to attach to specific proteins on the surface of the cells they enter, so most viruses only infect one type of host.
Once in a cell, viruses set about copies of themselves on a massive scale, but they are more interested in speed than in accuracy. Changes in the RNA or DNA arrangement, called mutations, happen all the time. Usually the altered code is meaningless, but in some cases a mutation enables the virus to infect a different host. The swine flu virus H1N1 developed mutations that let it spread to humans. What does spread actually mean “on the ground,” as they say? It means that the virus is shed in body fluids such as mucus, feces, urine, or blood and scattered through dust or droplets in the air which can end up on mucous membranes in the mouth, nose, or eyes of another host through touching or breathing the infectious particle.
Picture people working in a crowded pig barn, the air full of particles. Swine flu started in North America with people taking care of infected pigs and spread with the soldiers sent to fight in World War I until the flu became a pandemic in 1918-19 that killed at least 50 million people worldwide. A virus that makes that leap from an animal host to the human species is called a zoonosis. Sixty percent of all human infectious diseases started this way. We all know a few. Rabies, for example, and West Nile Virus. Influenza and the coronavirus diseases SARS, MERS, and COVID-19.
It takes close continued contact for the virus to mutate just right to make that leap to another species, human or not. But throughout history humans have come into close contact with other species in a number of situations. Farming, clearing rainforests, and “wet markets” are a few examples.
Reading about “wet markets,” I realized that of course they are everywhere. The distribution of meat, fish, and poultry in America today depends on refrigeration on a scale not seen throughout most of the world, let alone through most of history. Without energy-intensive refrigeration the safest way to assure freshness and quality of meat products is to check out the live animal before it is butchered. Have you ever been in a restaurant which had displayed live lobsters in a salt water tank? As a child I remember seeing live hens and other birds for sale in Iranian markets. Who would buy a dead chicken or a dead fish?
From a virus mutation point of view, the riskiest wet market would be one with crates of wild animals–porcupines, palm civets, pangolins, snakes, and birds–stacked on top of each other all exposed to each other’s waste products. Viruses are shed all over the place with great potential to get into a new host or even get mixed with another virus’ RNA inside a new host. Research now indicates that our newest coronavirus might have been transmitted via the pangolin, a mammal found mainly in Asia, which looks like an anteater. It’s protected by law, but poaching is widespread because it is valued both as a delicacy and as a medicine. Whether the coronavirus actually did spread to humans in a wet market is just one possibility at this point, however.
Tracing the possible hosts of a particular virus involves determining how close the genetic sequence of the coronavirus in one host is to that of the coronavirus in another host. It’s accomplished through a new science (i.e. wasn’t around when I was in college) using a combination of computing and biology, called bioinformatics. How closely one animal’s coronavirus genome matches another is expressed in percentages, such as 76 percent alike or 95 percent alike. Virus transfers like horseshoe bat to pangolin to person are under investigation and can only be expressed as probabilities at this time.
Bats serve as a reservoir host for several coronaviruses, meaning they can carry the viruses without contracting the disease. The pangolin appears to be an intermediate host, just as camels for MERS and civets for SARS. The intermediate host introduces the virus to humans, but the real damage comes when humans spread viruses to each other especially through our wide-ranging air travel networks.
How bats can harbor viruses without succumbing to disease is the subject of ongoing laboratory research. But the fact is that viruses mutate continuously in ways that sometimes enable them to move from one species to another. Sometimes that transferred virus will cause a respiratory disease that passes rapidly from one person to another. If such a disease has an incubation period that gives the person a few days before they feel ill, we have the perfect storm for a pandemic.
That’s what happened with COVID-19. Regardless of whether this particular coronavirus first got into humans in a laboratory, a wet market, or a superspreader event, animal to human virus transfer has happened before and will happen again because there are more of us than ever before, we impact the environment more than ever before, and we travel more than ever before in history. We can at least start by having procedures in place so that we can minimize the damage of this pandemic and the ones yet to come.
Today’s Notable Headlines
“Engineer? Cancer expert? Physicist? They’re coronavirus researchers now,” Amina Kahn, Los Angeles Times, May 29, 2020. https://www.latimes.com/science/story/2020-05-29/scientists-become-coronavirus-researchers
“U.S. and Chinese Scientists Trace Evolution of Coronaviruses in Bats,” New York Times, June 1, 2020. https://www.nytimes.com/2020/06/01/science/coronavirus-bats-wuhan.html
“The Chinese CDC now says the coronavirus didn’t jump to people at the Wuhan wet market — instead, it was the site of a super-spreader event,” Business Insider, May 28, 2020. https://news.yahoo.com/chinese-cdc-now-says-coronavirus-224900090.html
“China Rules Out Animal Market and Lab as Coronavirus Origin,” Wall Street Journal, May 26, 2020. https://www.wsj.com/articles/china-rules-out-animal-market-and-lab-as-coronavirus-origin-11590517508
Section 6.3 Viruses: Structure, Function, and Uses, National Institutes of Health, https://www.ncbi.nlm.nih.gov/books/NBK21523/
“PANGOLINS: WHAT ARE THEY AND WHY ARE THEY LINKED TO COVID-19?” Inverse, https://www.inverse.com/science/pangolins-explained
“Why They’re Called ‘Wet Markets’ — And What Health Risks They Might Pose,” NPR, Goats and Soda, Jan. 31, 2020. https://www.npr.org/sections/goatsandsoda/2020/01/31/800975655/why-theyre-called-wet-markets-and-what-health-risks-they-might-pose
“Coronavirus: Revenge of the Pangolins? China has banned the trade of wildlife, suspecting that exotic animals infected humans. What will that really do?,” The New York Times, Mar. 5, 2020. https://www.nytimes.com/2020/03/05/opinion/coronavirus-china-pangolins.html
Spillover: Animal Infections and the Next Human Pandemic, David Quammen, W. W. Norton & Company; Reprint edition (October 1, 2012).
“New Coronavirus ‘Won’t Be The Last’ Outbreak To Move From Animal To Human,” NPR, Goats and Soda, Feb. 5, 2020. https://www.npr.org/sections/goatsandsoda/2020/02/05/802938289/new-coronavirus-wont-be-the-last-outbreak-to-move-from-animal-to-human
Science Focus, the home of BBC Science Focus Magazine. https://www.sciencefocus.com/science/how-do-viruses-jump-from-animals-to-humans-2/
“Coronavirus spread: Why blame bats?” NPR, Goats and Soda, Feb. 9, 2020. https://www.mercurynews.com/2020/01/29/coronavirus-spread-why-point-the-finger-at-bats/
Why am I doing this?
The coronavirus pandemic will be indelibly written on our memories just as the Great Depression or the Battle of Britain left their mark on past generations. It is my intention to journal the events of these days from three perspectives: as a retired medical technologist, a historian (Ph.D., 2014), and an ordinary person living through an extraordinary crisis.
You are on History’s Edge.