As severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to circulate around the world, ecologists have become increasingly concerned about the potential for cross-species transmission of the virus from humans to susceptible wildlife species.
Previous studies have highlighted the virus’s ability to survive in water of varying pH levels and temperatures, and also its persistence through stages of wastewater treatment.
Now, researchers in Italy, in a recent pre-print – available to read in full on the bioRxiv*server – have identified a number of marine mammal species native to Italian seawaters that may be highly susceptible to the disease. Additionally, these species inhabit ocean areas where the virus may be present even after receiving sewage treatment, thus highlighting the need for strict sewage improvement plans.
SARS-CoV-2 is zoonotic in origin and binds to angiotensin-converting enzyme 2 (ACE2), an enzyme attached to the cell membranes of animal cells predominantly found in the lungs, heart and kidneys.
Due to the high degree of homology between humans and some animal ACE2, the risk of cross-species infection is greatly increased in those species. Thus, local outbreaks within wildlife populations must be prevented where possible.
Additionally, SARS-CoV-2 is known to be able to survive many of the treatment stages undergone in wastewater, and may be passed back into natural water sources. Studies have shown that the virus can remain active for up to 25 days, suspended in 5 °C water, and able to remain intact through pH levels between 3 and 10.
Taken together, there is a significant risk of wild marine mammals encountering and thus contracting the virus from sources originating from wastewater treatment plants. Especially in the case of some cetaceans, which are highly social, the risk of local outbreaks in aquatic wildlife is increased even more so.
Determining mammals at risk
The research team identified 15 marine mammal species (12 regular, 3 irregular) that inhabit the seas surrounding Italy.
Of these, they were able to acquire ACE2 sequencing from 9 of these, and compared the homology to human ACE2. They determined 7 species as being “high risk”, the remaining 2 as “medium risk”.
Risk of exposure and wastewater treatment quality
Wastewater powerplants typically perform up to three levels of treatment on sewage water. Although most plants in Italy carry out at least secondary treatment, SARS-CoV-2 has known to be able to survive both primary and secondary treatment plants.
Following this, the researchers identified the North Adriatic Sea and the Ligurian Sea as at-risk basins, where untreated or insufficiently treated water discharge from wastewater plants may ultimately gather, from the Po and Arno rivers. They also note an additional risk factor for the Central Adriatic, the Northern and Southern Ionian, and the South-Eastern Tyrrhenian seas, where some local plants have lower sanitization guarantees. Furthermore, they describe potential high-risk areas where flooding or over-spilling from plants may result in SARS-CoV-2 enriched water sources.
Immunohistochemical characterization of ACE2
SAR-CoV-2 primarily binds to ACE2 in respiratory cells. However, the lungs of cetaceans undergo physiological and anatomical changes for deep diving that terrestrial mammals are incapable of. The research team, therefore, wished to determine whether this might affect ACE-2 immune response to SARS-CoV-2.
They confirmed the expression of ACE2 antibodies in lung tissue of all the examined species, signaling that recovery and resistance to SARS-CoV-2 can be achieved in these Italian cetaceans.
The researchers highlight areas of the Italian sealine that may be of increased risk to exposing marine mammals to SARS-CoV-2. As of yet, the virus has not been known to survive in seawater, although it is capable of surviving in many other waterbodies that animals may come into contact with.
The conservation of Mediterranean cetaceans is greatly important at present, as many of the native species suffer from a large number of anthropological effects occurring in their environment.
Amongst net entanglement, boat collisions, plastic ingestion, chemical pollution and many other factors, potential virus infection is just another issue that must be addressed for aquatic mammals.
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.