Potential SARS-CoV-2 Susceptibility of Cetaceans Stranded along the Italian Coastline

Abstract

Due to marine mammals’ demonstrated susceptibility to SARS-CoV-2, based upon the homology level of their angiotensin-converting enzyme 2 (ACE2) viral receptor with the human one, alongside the global SARS-CoV-2 occurrence and fecal contamination of the river and marine ecosystems, SARS-CoV-2 infection may be plausibly expected to occur also in cetaceans, with special emphasis on inshore species like bottlenose dolphins (Tursiops truncatus). Moreover, based on immune and inflammatory responses to SARS-CoV-2 infection in humans, macrophages could also play an important role in antiviral defense mechanisms. In order to provide a more in-depth insight into SARS-CoV-2 susceptibility in marine mammals, we evaluated the presence of SARS-CoV-2 and the expression of ACE2 and the pan-macrophage marker CD68. Aliquots of tissue samples, belonging to cetaceans stranded along the Italian coastline during 2020–2021, were collected for SARS-CoV-2 analysis by real-time PCR (RT-PCRT) (N =43) and Immunohistochemistry (IHC) (N = 59); thirty-two aliquots of pulmonary tissue sample (N = 17 Tursiops truncatus, N = 15 Stenella coeruleoalba) available at the Mediterranean Marine Mammal Tissue Bank (MMMTB) of the University of Padua (Legnaro, Padua, Italy) were analyzed to investigate ACE2 expression by IHC. In addition, ACE2 and CD68 were also investigated by Double-Labeling Immunofluorescence (IF) Confocal Laser Microscopy. No SARS-CoV-2 positivity was found in samples analyzed for the survey while ACE2 protein was detected in the lower respiratory tract albeit heterogeneously for age, gender/sex, and specie, suggesting that ACE2 expression can vary between different lung regions and among individuals. Finally, double IF analysis showed elevated colocalization of ACE2 and CD68 in macrophages only when an evident inflammatory reaction was present, such as in human SARS-CoV-2 infection.

SARS-CoV-2 Susceptibility of Domestic Animals and Wildlife in the Media Narrative

“…Noteworthily, at least 29 different animal species, both domestic and wild, have been hitherto deemed naturally and/or experimentally susceptible to SARS-CoV-2 infection. These include, among others, wild cetaceans such as bottlenose dolphins (Tursiops truncatus), based upon the homology level of their angiotensin-converting enzyme 2 (ACE2) viral receptor with the human one [3]. In this respect, while it should be firmly kept in mind, on one hand, that interhuman transmission is by far the prevailing mode of SARS-CoV-2 infection, it should be additionally emphasized, on the other hand, that clear-cut evidence of "man-to-animal viral spillover" and, to a lesser extent, of "animal-to-man viral spillback" events has been clearly documented.…”