38: Bat ancestors, recombination, and rapid travel: origins of SARS-CoV and SARS-CoV-2

Pekar JE et al., Cell - Recombination-aware, whole-genome analyses of sarbecoviruses show that genomic fragments very closely related to SARS-CoV and SARS-CoV-2 circulated in horseshoe bats only years before human emergence. Phylogeography places recent ancestors in western China and northern Laos and indicates movement patterns inconsistent with bat-only dispersal, implicating intermediate hosts or wildlife trade. Key terms: sarbecovirus, recombination, phylogeography, horseshoe bats, zoonotic spillover.

Study Highlights:
The authors mapped recombination breakpoints and analyzed non-recombinant regions (NRRs) across sarbecovirus genomes to infer separate evolutionary histories for SARS-CoV-1-like and SARS-CoV-2-like viruses. Closest-inferred bat virus ancestors for both human SARS-CoVs often date just 1–6 years before human emergence in specific NRRs. Phylogeographic reconstructions place those recent ancestors in western China and northern Laos/Yunnan, and show viral diffusion rates approximating horseshoe bat movement. The geographic distances and required dispersal velocities make bat-only spread to emergence sites unlikely, supporting a role for intermediate hosts or wildlife trade.

Conclusion:
Non-recombinant genome segments reveal very recent bat ancestors of SARS-CoV and SARS-CoV-2 that likely could not have reached human emergence sites by bat movement alone, highlighting the importance of whole-genome surveillance in bats, targeted sampling in Southwest China and Northern Laos, and monitoring of wildlife trade pathways.

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Article title:
The recency and geographical origins of the bat viruses ancestral to SARS-CoV and SARS-CoV-2

First author:
Pekar JE

Journal:
Cell

DOI:
10.1016/j.cell.2025.03.035

Reference:
Pekar JE, Lytras S, Ghafari M, et al. The recency and geographical origins of the bat viruses ancestral to SARS-CoV and SARS-CoV-2. Cell. 2025;188:1–17. doi:10.1016/j.cell.2025.03.035

License:
This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) – https://creativecommons.org/licenses/by/4.0/

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Episode link: https://basebybase.com/episodes/recency-geographical-origins-bat-viruses-sars-cov-sars-cov-2

QC:
This episode was checked against the original article PDF and publication metadata for the episode release published on 2025-06-07.

QC Scope:
- article metadata and core scientific claims from the narration
- excludes analogies, intro/outro, and music
- transcript coverage: Audited the transcript sections describing non-recombinant regions (NRRs), recombination-aware dating, the Prisoner of War (PoW) molecular clock, phylogeography, dispersal velocities, geographic origins of closest bat ancestors, and implications about wildlife trade as a bridge to emergence.
- transcript topics: Recombination and non-recombinant regions (NRRs); NRR-based dating and closest-inferred bat ancestors; Prisoner of War (PoW) molecular clock and substitution saturation; Phylogeography and isolation by distance; Dispersal velocities and bat-host diffusion; Geographic origins of closest bat ancestors (SARS-CoV-1 in Western China; SARS-CoV-2 in Yunnan/Northern Laos)

QC Summary:
- factual score: 10/10
- metadata score: 10/10
- supported core claims: 8
- claims flagged for review: 0
- metadata checks passed: 4
- metadata issues found: 0

Metadata Audited:
- article_doi
- article_title
- article_journal
- license

Factual Items Audited:
- Closest bat-virus ancestors for SARS-CoV-1 circulated in bats in 2001 (1 year before SARS-CoV-1 emergence in 2002; NRR14).
- Closest bat-virus ancestors for SARS-CoV-2 circulated in bats in 2014 (two NRRs with closest ancestors in 2014; HPD intervals given).
- SARS-CoV-1-like ancestors inferred in Western China (Yunnan, Sichuan, Guizhou) and SARS-CoV-2-like ancestors in Yunnan or Northern Laos.
- Outbreaks in Guangzhou (SARS-CoV-1) and Wuhan (SARS-CoV-2) are ~1000 km from bat-ancestor circulation sites.
- Weighted diffusion coefficients: SARS-CoV-1-like ~1666 km^2/year; SARS-CoV-2-like ~740 km^2/year.
- Isolation by distance indicates viruses spread at rates matching bat host movement; bat dispersal is relatively local.

QC result: Pass.