Dear Editor,
The recent description of a human infection caused by a highly divergent SARS-CoV-2 lineage (B.1.641) circulating among white-tailed deer (Odocoileus virginianus) in Ontario, Canada (1) is a matter of concern. Indeed, white-tailed deer have been already shown to be highly susceptible to SARS-CoV-2 infection, thereby supporting in a very efficient way, under natural conditions, the intra-species transmission of multiple “variants of concern” (VOCs) and “variants of interest” infecting people (2). Furthermore, phylogenomic analyses have provided clear-cut evidence for the natural selection in white-tailed deer of one of the most divergent SARS-CoV-2 lineages hitherto identified (B.1.641), harbouring 76 mutations (37 of which had not been previously detected in human viral isolates) and sharing a quite recent common ancestry with a mink SARS-CoV-2 strain from Michigan (1). Although the B.1.641 viral isolate from white-tailed deer and a human patient in Ontario was not characterized by the S:Y453F mutation reported among intensely reared mink in Denmark, from which the “cluster 5” VOC subsequently spilled back into humans (3), the gregarious nature of white-tailed deer should be adequately taken into account as a host ecology factor efficiently supporting SARS-CoV-2 intra-species replication and spread, in a similar manner to what happened – yet under “artificial” conditions – in mink farms in Denmark and elsewhere (3).
Enhanced viral replication could lead, in turn, to the progressive acquirement of “non-silent” mutations in the SARS-CoV-2 genetic make-up, considering its genome consists of approximately 30,000 bases, with each replication cycle implying the occurrence, as an average, of 1 mutation/10,000 nucleotides (4). Indeed, by progressively undergoing mutational events in both naturally and “artificially” gregarious species like white-tailed deer and mink, respectively, the possibility that new, highly divergent and pathogenic SARS-CoV-2 lineages could emerge from “animal communities” and infect people should be seriously taken into account.
Luckily enough, the interhuman transmission efficiency of the hitherto characterized SARS-CoV-2 strains recovered from animals appears to be quite limited at this stage.
As a concluding remark, while also considering the animal vaccination opportunity – with special emphasis on wildlife species highly susceptible to SARS-CoV-2 infection (5) -, a rigorous and continuous eco-epidemiological surveillance activity, to be implemented through a multidisciplinary, holistic, evidence- and One Health-based approach, would be needed in order to adequately monitor these crucial phenomena and, more in general, the highly intriguing SARS-CoV-2 trajectories from animals to mankind and viceversa.
References
1. Pickering B., et al. (2022). Divergent SARS-CoV-variant emerges in white-tailed deer with deer-to-human transmission. Nat. Microbiol. https://doi.org/10.1038/s41564-022-01268-9.
2. Hale V.L., et al. (2022). SARS-CoV-2 infection in free-ranging white-tailed deer. Nature 602, 481-486.
3. Lassaunière R., et al. (2021). In vitro characterization of fitness and convalescent antibody neutralization of SARS-CoV-2 cluster 5 variant emerging in mink at Danish farms. Front. Microbiol. 12, 698944. doi: 10.3389/fmicb.2021.698944.
4. Di Guardo G. (2022). Is gain of function a reliable tool for establishing SARS-CoV-2 origin?. Adv. Microbiol. 12, 103-108. doi: 10.4236/aim.2022.123009.
5. Di Guardo, G. (2022). We should be vaccinating domestic and wild animal species against CoViD-19. Vet. Rec. 190, 293.
SARS-CoV-2 infections acquired from animals: How much should we worry?