{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,27]],"date-time":"2026-02-27T01:34:27Z","timestamp":1772156067284,"version":"3.50.1"},"reference-count":27,"publisher":"The Royal Society","issue":"10","license":[{"start":{"date-parts":[[2025,10,1]],"date-time":"2025-10-01T00:00:00Z","timestamp":1759276800000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"},{"start":{"date-parts":[[2025,10,1]],"date-time":"2025-10-01T00:00:00Z","timestamp":1759276800000},"content-version":"tdm","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["royalsocietypublishing.org"],"crossmark-restriction":true},"short-container-title":["R. Soc. Open Sci."],"published-print":{"date-parts":[[2025,10]]},"abstract":"<jats:p>\n                    This study utilized faecal samples from synanthropic rodents collected during September\u2013December of 2020 from a public park in southern Mexico City, previously identified as positive for SARS-CoV-2, to perform molecular identification of the viral variant. Typing was successful for two\n                    <jats:italic toggle=\"yes\">Mus musculus<\/jats:italic>\n                    and one\n                    <jats:italic toggle=\"yes\">Rattus norvegicus<\/jats:italic>\n                    , revealing Omicron variants BA.5.2 (from a rat) and BA.5.1.17 (from mice). Additionally, confirmation from a reference centre and Global Initiative on Sharing All Influenza Data (GISAID) analysis verified the presence of the Omicron variant. By considering three primary hypotheses regarding Omicron's origin and integrating these findings with concurrent events in Mexico during the initial wave of SARS-CoV-2, it is reasonable to suggest that the variant\u2019s emergence may stem from a combination of a \u2018silent spread\u2019 (indicating circulation among populations with limited viral monitoring and sequencing) and a \u2018mouse origin\u2019 (where the progenitor of Omicron transitioned from humans to mice, acquiring mutations that enhanced its ability to infect that host, before re-emerging in humans). Consequently, our results indicate that Omicron was present in urban rodents a year prior to its official emergence, amplified by the conditions existing during the first wave of COVID-19 in Mexico.\n                  <\/jats:p>","DOI":"10.1098\/rsos.250926","type":"journal-article","created":{"date-parts":[[2025,10,21]],"date-time":"2025-10-21T23:07:13Z","timestamp":1761088033000},"update-policy":"https:\/\/doi.org\/10.1098\/crossmark-policy","source":"Crossref","is-referenced-by-count":0,"title":["A clue to clarify the origin of Omicron"],"prefix":"10.1098","volume":"12","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-6140-8398","authenticated-orcid":true,"given":"Fernando","family":"Martinez-Hernandez","sequence":"first","affiliation":[{"name":"Hospital General Dr Manuel Gea Gonzalez","place":["Ciudad de Mexico, Mexico"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6679-016X","authenticated-orcid":true,"given":"Claudia Irais","family":"Mu\u00f1oz-Garcia","sequence":"additional","affiliation":[{"name":"Departamento de Produccion Agricola y Animal, Universidad Autonoma Metropolitana\u2014Unidad Xochimilco","place":["Coyoac\u00e1n, Mexico"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6264-3907","authenticated-orcid":true,"given":"Emilio","family":"Rendon-Franco","sequence":"additional","affiliation":[{"name":"Departamento de Produccion Agricola y Animal, Universidad Autonoma Metropolitana\u2014Unidad Xochimilco","place":["Coyoac\u00e1n, Mexico"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jos\u00e9 Antonio","family":"Ocampo Cervantes","sequence":"additional","affiliation":[{"name":"Centro de investigaciones biol\u00f3gicas y acu\u00edcolas de Cuemanco, Unidad Xochimilco, Universidad Autonoma Metropolitana","place":["Ciudad de M\u00e9xico, Mexico"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5656-0942","authenticated-orcid":true,"given":"Rigoberto","family":"Hernandez-Castro","sequence":"additional","affiliation":[{"name":"Hospital General Dr Manuel Gea Gonzalez","place":["Ciudad de Mexico, Mexico"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Angelica","family":"Olivo-Diaz","sequence":"additional","affiliation":[{"name":"Hospital General Dr Manuel Gea Gonzalez","place":["Ciudad de Mexico, Mexico"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0522-8357","authenticated-orcid":true,"given":"Mirza","family":"Romero-Valdovinos","sequence":"additional","affiliation":[{"name":"Hospital General Dr Manuel Gea Gonzalez","place":["Ciudad de Mexico, Mexico"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2534-9447","authenticated-orcid":true,"given":"Pablo","family":"Maravilla","sequence":"additional","affiliation":[{"name":"Hospital General Dr Manuel Gea Gonzalez","place":["Ciudad de Mexico, Mexico"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0666-6204","authenticated-orcid":true,"given":"Nelly Raquel","family":"Gonzalez-Arenas","sequence":"additional","affiliation":[{"name":"Hospital General Dr Manuel Gea Gonzalez","place":["Ciudad de Mexico, Mexico"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2733-1654","authenticated-orcid":true,"given":"Guiehdani","family":"Villalobos","sequence":"additional","affiliation":[{"name":"Departamento de Produccion Agricola y Animal, Universidad Autonoma Metropolitana\u2014Unidad Xochimilco","place":["Coyoac\u00e1n, Mexico"]}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"175","published-online":{"date-parts":[[2025,10,22]]},"reference":[{"key":"e_1_3_7_2_2","unstructured":"World Health Organization. 2021 Tracking SARS-CoV-2 variants. 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