The Times Australia
The Times World News

.
The Times Real Estate

.

New preliminary evidence suggests coronavirus jumped from animals to humans multiple times

  • Written by Hamish McCallum, Director, Centre for Planetary Health and Food Security, Griffith University

The origin of the SARS-CoV-2 virus, which has caused the COVID-19 pandemic, has been hotly debated.

This debate has caused substantial difficulties in the Australia-China relationship, with a call by Foreign Minister Marise Payne for another inquiry into its origin[1] being considered by China as a hostile act.

What’s not in doubt is the closest relatives of the virus are found in bats[2]. How, where and when the virus spilled over into humans is the contentious issue.

One widely supported hypothesis is the spillover occurred in the “wet markets” of Wuhan, where many species of wildlife from across China are held in crowded conditions.

However, there’s no evidence the species of bats in which the closest relatives of SARS-CoV-2 are found were sold through the Wuhan wet markets at any time in the two years before the pandemic[3]. This hypothesis requires the existence of a “bridge host”, another species that becomes infected via spillover from the original bat hosts, and then passes the virus onto humans.

Bridge hosts are well-known in many emerging human diseases. For example, Hendra virus, which my group studies, has flying foxes as its reservoir. Hendra spills over to horses with some frequency[4]. Horses then amplify the virus as a bridge host and can infect humans.

Fortunately, this is extremely rare, with only seven known cases[5]. Tragically, four of those people died. Hendra has never been known to spread directly from flying foxes to humans.

Read more: I was the Australian doctor on the WHO's COVID-19 mission to China. Here's what we found about the origins of the coronavirus[6]

More evidence a lab leak is very unlikely

A second, much more contentious hypothesis[7] is the origin of the pandemic was the result of a “lab leak”.

Wuhan has one of the most sophisticated virological laboratories in China, and the laboratory does work on bat viruses. The suggestion is the virus may have inadvertently been released into the general community via one of the workers. No direct evidence supports this hypothesis.

A new pre-print study, released online this month[8], provides strong evidence[9] to support the “natural spillover” hypothesis, with results that are hard to reconcile with the “lab leak” hypothesis.

The study is yet to be peer reviewed. But it’s based on a detailed examination of the genetic sequences of two early lineages obtained from people infected in late 2019 and early 2020.

For convenience, these two lineages are called A and B. The two lineages differ by just two nucleotides (letters in the genetic code) at two different key sites in the genetic sequence.

If there was a single lab escape event, the separation into lineages A and B must have happened after the lab escape. We would therefore expect to see a substantial number of intermediate lineages, with the lineage A nucleotide at one site, and the lineage B nucleotide at the other site.

However, if almost all of the genetic sequences obtained from humans are “pure” lineage A or pure lineage B, this suggests there were at least two different spillover events, either directly from bats or via bridge hosts.

And the evolution of the two lineages occurred before humans were infected.

The researchers downloaded all complete genetic sequences for SARS-CoV-2 that had been lodged in a widely used genomic database. Of these sequences, 369 were lineage A, 1,297 were lineage B and just 38 were intermediates.

Read more: Why it will soon be too late to find out where the COVID-19 virus originated[10]

Genetic sequencing isn’t perfect. Close examination of the 38 intermediates strongly suggested they were more likely to be sequencing errors of pure lineage A or lineage B than to be true intermediates.

The genetic evidence, therefore, suggests very strongly there have been at least two separate spillover events into human populations, one being from lineage A and another being from lineage B.

Did a human bring SARS-CoV-2 to the wet markets?

The data don’t tell us there have been only two spillover events — there may have been more. Nor do they tell us whether these spillovers happened directly from bats, or whether some or all happened via an intermediate bridge host.

A Nature news article suggests this evidence points to the spillover having happened via the wildlife trade[11], but I think this is taking it a step too far.

While some of the wildlife species sold through the Wuhan wet market can indeed become infected with SARS-CoV-2 (for example raccoon dogs[12] and mink[13]), there’s no evidence any sold through the market were infected.

Many of the earliest human viral sequences (all lineage B) were recovered from the Wuhan seafood market, but wet markets and abattoirs are well-known to be places where the SARS-CoV-2 virus spreads very well from human to human.

So, it may have been a human who brought the virus to the Wuhan seafood market, rather than a species of wildlife.

One thing we do know is this pandemic originated through a human coming in contact with another species infected with the virus.

It’s unknown whether this was a bat or a bridge host, and whether this contact occurred in a wildlife market, or in a bat cave, or somewhere else entirely different.

Nevertheless, as humans encroach more and more on the habitats of wild animals and as wild animals are brought more frequently into close contact with humans, we can expect further spillovers and pandemics to occur.

Read more: How do viruses mutate and jump species? And why are 'spillovers' becoming more common?[14]

References

  1. ^ Marise Payne for another inquiry into its origin (www.abc.net.au)
  2. ^ closest relatives of the virus are found in bats (www.nature.com)
  3. ^ two years before the pandemic (www.nature.com)
  4. ^ with some frequency (royalsocietypublishing.org)
  5. ^ seven known cases (www.health.nsw.gov.au)
  6. ^ I was the Australian doctor on the WHO's COVID-19 mission to China. Here's what we found about the origins of the coronavirus (theconversation.com)
  7. ^ contentious hypothesis (theconversation.com)
  8. ^ released online this month (virological.org)
  9. ^ strong evidence (www.nature.com)
  10. ^ Why it will soon be too late to find out where the COVID-19 virus originated (theconversation.com)
  11. ^ points to the spillover having happened via the wildlife trade (www.nature.com)
  12. ^ raccoon dogs (wwwnc.cdc.gov)
  13. ^ mink (www.sciencedirect.com)
  14. ^ How do viruses mutate and jump species? And why are 'spillovers' becoming more common? (theconversation.com)

Read more https://theconversation.com/new-preliminary-evidence-suggests-coronavirus-jumped-from-animals-to-humans-multiple-times-168473

The Times Features

How to Protect Your Garden Trees from Wind Damage in Australia

In Australia's expansive landscape, garden trees hold noteworthy significance. They not only enhance the aesthetic appeal of our homes but also play an integral role in the local...

Brisbane Homeowners Warned: Non-Compliant Flexible Hoses Pose High Flood Risk

As a homeowner in Brisbane, when you think of the potential for flood damage to your home, you probably think of weather events. But you should know that there may be a tickin...

Argan Oil-Infused Moroccanoil Shampoo: Nourish and Revitalize Your Hair

Are you ready to transform your hair from dull and lifeless to vibrant and full of life? Look no further than the luxurious embrace of Argan Oil-Infused Moroccanoil Shampoo! In a...

Building A Strong Foundation For Any Structure

Building a home or commercial building can be very exciting. The possibilities are endless and the future is interesting. You can always change aspects of the building to meet the ...

The Role of a Family Dentist: Why Every Household Needs One

source A family dentist isn’t like your regular dentist who may specialise in a particular age group and whom you visit only when something goes wrong. A family dentist takes proa...

Benefits of Getting an Online Medical Certificate

Everyone has experienced it. Rather than taking a break, you drag yourself to the doctor's office, where you have to wait in lengthy lines, and then you have to hurry to get that...

Times Magazine

"Eternal Nurture" by Cara Barilla: A Timeless Collection of Wisdom and Healing

Renowned Sydney-born author and educator Cara Barilla has released her latest book, Eternal Nurture, a profound collection of inspirational quotes designed to support mindfulness, emotional healing, and personal growth. With a deep commitment to ...

How AI-Driven SEO Enhancements Can Improve Headless CMS Content Visibility

Whereas SEO (search engine optimization) is critical in the digital landscape for making connections to content, much of it is still done manually keyword research, metatags, final tweaks at publication requiring a human element that takes extensiv...

Crypto Expert John Fenga Reveals How Blockchain is Revolutionising Charity

One of the most persistent challenges in the charity sector is trust. Donors often wonder whether their contributions are being used effectively or if overhead costs consume a significant portion. Traditional fundraising methods can be opaque, with...

Navigating Parenting Arrangements in Australia: A Legal Guide for Parents

Understanding Parenting Arrangements in Australia. Child custody disputes are often one of the most emotionally charged aspects of separation or divorce. Parents naturally want what is best for their children, but the legal process of determining ...

Blocky Adventures: A Minecraft Movie Celebration for Your Wrist

The Minecraft movie is almost here—and it’s time to get excited! With the film set to hit theaters on April 4, 2025, fans have a brand-new reason to celebrate. To honor the upcoming blockbuster, watchfaces.co has released a special Minecraft-inspir...

The Ultimate Guide to Apple Watch Faces & Trending Wallpapers

In today’s digital world, personalization is everything. Your smartwatch isn’t just a timepiece—it’s an extension of your style. Thanks to innovative third-party developers, customizing your Apple Watch has reached new heights with stunning designs...

LayBy Shopping