White-tailed deer, another SARS-CoV-2-susceptible species
An interesting commentary published in Nature (Mallapaty, 2021) reports that a vast proportion (40%) of white-tailed deer (Odocoileus virginianus) from North-Eastern USA were proven to harbour anti-SARS-CoV-2 antibodies in their blood serum.
This implies two important things, namely that:
1) the aforementioned deers had been previously exposed to the virus;
2) these deer, once having acquired the infection - most likely from SARS-CoV-2-infected humans - were (most likely) able to transmit the virus to their conspecifics living in close proximity with them.
Based upon the above, white-tailed deer add themselves to the (already) long list of SARS-CoV-2-susceptible animal species, either naturally or experimentally, including - among others - cats, dogs, racoon dogs, lions, tigers, snow leopards, pumas, ferrets, hamsters, otters, gorillas and mink (Di Guardo, 2020; Di Guardo, 2021a).
Within such context, the viral-host interaction dynamics occurring in mink appear to be of special concern, provided that - once acquired from infected humans - SARS-CoV-2 was shown to evolve into a peculiar "variant of concern" (VOC) named "cluster 5" inside the body of mink, which were additionally proven to be able to re-transmit the mutated virus to humans (Di Guardo, 2021a). This has been repeatedly documented, more than one year ago, in intensely reared/bred mink from The Netherlands and from Denmark, where approximately 17 million mink had to be killed as a consequence of the public health hazard posed by them.
In this respect, based upon the fact that the "artificial, man-made gregarious appearance" characterizing intensive mink herds (paradoxically) shares a number of features in common with the ecological behaviour of white-tailed deer, living together in more or less large groups of animals, there are plausibly more chances - for both species - of acquiring and transmitting SARS-CoV-2 infection to their conspecifics in close proximity to them.
This is additionally supported by the primary sequence similarities existing between the viral ACE-2 receptor of white-tailed deer and mink, on one side, and the human one, on the other, as also reported by us for a number of cetacean species inhabiting the Western Mediterranean (Audino et al., 2021).
What does all this mean in terms of "SARS-CoV-2 infection's evolutionary dynamics"?
We know there are almost 8 billion people living on Earth and that the "official numbers" of the SARS-CoV-2 pandemic show that the virus has thus far (at the date of September 08, 2021) infected approximately 220 million humans, with a death toll of nearly 4.6 millions worldwide (World Health Organization/WHO, 2021). We also kmow that the vast majority (over 70%) of people vaccinated against SARS-CoV-2 live in no more than 15 Countries, with the so-called "herd immunity level" (which is now estimated to be reached when around 85-90% of the human population will have received a full vaccination, as a consequence of the widespread circulation of the "Delta VOC") having been achieved, thus far, in none of these Countries, to the best of my knowledge. We additionally know that young people, who may still become infected quite easily, tend to display the clinical features of SARS-CoV-2 infection much less frequently than older adults and elderly people (many of whom are now fully vaccinated, luckily!), with many SARS-CoV-2-infected youngsters showing either no symptom(s) or very mild CoViD-19-associated/related clinical signs. While this is undoubtedly good news, on the "other side of the coin" there is an increased risk of viral transmission posed by asymptomatic, SARS-CoV-2-infected young people, with special reference to unvaccinated, older adults and "fragile" elderly patients.
Furthermore, by circulating "undetected" in young patients - many of whom are getting vaccinated in Italy as well as in other Countries - the chances for the virus to evolve into additional VOC and/or "variants of interest" (VOI), such as the recently described "Kappa", "Lambda" and "Mu" variants, will most likely get increased by far.
This appears to be true also for unvaccinated people and, most plausibly, also for a number of SARS-CoV-2-susceptible animal species, as clearly demonstrated for mink in relation to the "cluster 5 VOC" in The Netherlands and in Denmark.
With this in mind and in tight agreement with the One Health principle, mutually linking "human, animal and environmental health" to each other, I believe we should take into serious account the possibility/opportunity to vaccinate (also) SARS-CoV-2-susceptible animals, both domestic and wild ones (the latter ones not only from a health but also from a conservation perspective), against SARS-CoV-2 (Di Guardo, 2021a).
Indeed, of the many lessons this dramatic pandemic has taught us, the most important one is that we need a "holistic, multi-interdisciplinary strategy" to properly counteract and, most hopefully, prevent similar catastrophes in the years to come.
This is totally different, of course, from the "anthropocentric" and, consequently, "hospitalocentric" approach seen until now, which - albeit important - is by definition a "losing approach" if everything rotates around it.
Notwithstanding the above, it makes me very sad to remark - as a veterinary pathologist and past university professor for almost 20 years at an Italian veterinary medical faculty - that not even one single veterinarian sits yet on the "Italian CoViD-19 Scientific Committee" (popularly known with the acronym "CTS"), after more than 19 months since its official institution (Di Guardo, 2021b)!
1) Audino T., et al. (2021) - Animals.
2) Di Guardo G. (2020) - Journal of Comparative Pathology.
3) Di Guardo G. (2021a) - Veterinary Record.
4) Di Guardo G. (2021b) - BMJ.
5) Mallapaty S. (2021) - Nature.
Competing interests: No competing interests