Tracing the Zoonotic Origins of SARS-CoV-2

February 22, 2024

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As COVID-19 tragically reminded, viruses emerging from animal reservoirs remain an enduring threat. But pinpointing origins of zoonotic spillovers like SARS-CoV-2 proves notoriously difficult, often taking years. Still, piecing together clues around early zoonotic transmission events informs vigilance and perhaps prevention of future pandemic sparks.

Genomic analyses provide hints on SARS-CoV-2’s enigmatic ancestry – traced back to bat species through unknown intermediates. Ongoing animal reservoirs further complicate containment. Understanding coronaviruses’ complex evolutionary interplay with human and non-human hosts provides insights on what enables these cross-species jumps.

Defining Zoonotic Transmission of Novel Pathogens

Zoonosis refers to infectious diseases that spill over from vertebrate animals to humans, typically through intermediate hosts that facilitate viral adaptation towards exploiting new species.

Common zoonotic examples include:

  • Avian and swine influenza strains
  • Vector-borne diseases like Lyme, Zika, West Nile
  • Rabies cycling through carnivore reservoirs
  • Waterborne illness from livestock waste

Coronaviruses conspicuously zoonotic, having caused regional outbreaks like:

  • 2002-04 SARS epidemic
  • 2012-ongoing MERS cases
  • 2019 SARS-CoV-2 pandemic

Surveillance across widlife populations spotlights frequent zoonosis, with viruses like SARS-CoV-2 demonstrating ability to transmit onward between humans.

The Animal Origins of SARS-CoV-2

In the case of SARS-CoV-2 origins, genomic detective work points to bats as the ultimate viral reservoir from which early progenitor strains emerged over a decade ago.

No evidence indicates SARS-CoV-2 itself circulated in humans prior to late 2019. Crucially, connecting threads to bridge the bat-human species barrier remain undisclosed. Hypothesized wildlife intermediate hosts and direct spillover progenitors include:

  • Pangolins
  • Minks
  • Poultry
  • Snakes
  • Turtles
  • Cats

Debates continue regarding definitively tracing zoonotic events behind the disastrous COVID-19 pandemic. But appreciating this propensity of coronaviruses for navigating between species spotlights what vigilance awaits in the years ahead.

After Zoonotic Spillover: SARS-CoV-2 Reverse Zoonosis

Beyond originating from animal reservoirs itself, SARS-CoV-2 demonstrate capability for reverse zoonosis – transmitting back from humans into new potential animal hosts.

Detected susceptible species include:

  • Felines – Cats, lions, tigers, pumas
  • Mustelids – Ferrets, minks
  • White-tailed deer
  • Non-human primates
  • Small mammals like mice and hamsters

Such secondary zoonotic reservoirs frustrate containment, sustaining viral circulation through pet populations and wildlife. Adaptations facilitating humans-to-animals spread may redefine viral evolution trajectories.

Again by better appreciating zoonosis permeating both directions – animal to human and human back to animal – Context girds against future pandemic threats emerging from obscure corners of the natural world.

Drivers and Enablers of Coronavirus Zoonosis

Why do coronaviruses seem so prone to inter-species jumps underlying epidemics? Various biological properties and anthropogenic realities converge:

High Mutation Rates

Rapid mutation cycles driven by error-prone replication generate continual population diversity testing viability across hosts.

Recombination Potential

Simultaneous circulation of distinct lineages in the same hosts allows viral RNA recombination – fusing advantageous mutations that adapt to new species.

Broad Cell Receptor Tropisms

Coronavirus spike proteins bind a wide range of host receptors (ACE2 for SARS-CoV-2), preadapting opportunistic jumps.

Animal Market Proximity

Cultural practices like wildlife wet markets and industrial livestock enable sustained human-animal mingle zones primes for spillover events, as likely sparked COVID-19.

By appreciating all that enabled SARS-CoV-2 emergence, the world equips itself against future zoonotic threats lurking within ecosytems.

Frequently Asked Questions

Could domestic pets become long-term SARS-CoV-2 reservoirs?

Since cats, dogs and other mammalian pets clearly demonstrate susceptibility, they raise concerns around persistence reservoirs infectious to humans. But idiosyncratic transmission to pets seems unlikely to drive population-level spread comparable to human propagation.

How long might SARS-CoV-2 viably persist in bat populations?

Coronaviruses naturally circulate through certain bat species as chronic infections, potentially for decades. But the particular mutations adapting SARS-CoV-2 to humans may attenuate reservoiring in other species long-term through competitive exclusion by endemic strains.

If identified, should intermediate hosts face culling to curb reservoirs?

Despite short-term appeals, indiscriminate culling risks ecological calamity above any pandemic gains. SARS-CoV-2 has already pervaded global human circulation irrespective of ongoing animal presence. Prevention should center on altering anthropogenic drivers behind zoonotic spillover opportunities.

Could de-extinction restore missing ecosystem functionality inhibiting zoonosis?

Interesting hypothetical, but conservation priorities should focus on preserving existing complexity and limiting anthropogenic disturbances of wildlife rather than applying futuristic biotech fixes. The dynamics at play involve far more than single species.

What future zoonotic threats concern virologists currently?

Beyond predictable influenza strains, paramyxoviruses like Nipah virus capable of broad mammalian infectivity remain on watchlists for adaption risks. Coronaviruses harboring zoonotic risks also lurk within bats across Eurasia and Africa, necessitating ethical surveillance.

In summary, key points on SARS-CoV-2 origins:

  • Zoonotic virus spilling over from still-unknown animal reservoir(s)
  • Genomic links traced to bat progenitor viruses
  • Secondary human-to-animal transmission fuels new reservoirs
  • Combination of viral adaptability and human exposures drive emergence
  • Ongoing vigilance needed to mitigate future spillover risks

Appreciating the ever-shifting landscape of threats requires recognizing ecological complexity including our entanglement within. This offers dual perspectives – whether peering past the next pandemic’s kindling or spotting sparks among our own footsteps.


  1. Zhang, T., Wu, Q. & Zhang, Z. Probable Pangolin Origin of SARS-CoV-2 Associated with the COVID-19 Outbreak. Curr Biol 30, 1578–1585 (2020).
  2. Deng, J., Jin, Y., Liu, Y. et al. Serological responses against SARS-CoV-2 infection among animal models. Transbound Emerg Dis 68, 3316–3326 (2021).
  3. Su, S. et al. Epidemiology, Genetic Recombination, and Pathogenesis of Coronaviruses. Trends Microbiol. 24, 490-502 (2016).
  4. Melin, A. D. et al. COVID-19 reveals risky wildlife trade at odds with postdomestic ethics. Authorea Prepr. (2021).
  5. Banerjee, A. et al. Novel insights into immune systems of bats. Front. Immunol. 11:26 (2020).
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