Zoonoses are no respecter of biological boundaries and are notorious for crossing genus and even higher taxonomic boundaries. SARS-CoV-2 is no exception, the current outbreak most probably having originated in bats, a common source of human-affecting zoonoses throughout history. But it is not a one-way street, and the virus has been shown to spread from infected humans to a variety of other land mammals, including our domesticated animals and kept zoo species.
A recent troubling report, however, has indicated that sea mammals may be part of a next wave of likely candidates for infection, put at risk by the current human pandemic and environmental degradation on a global scale, according to a the results of a genomic analysis of four major groups of sea mammals.
Researchers Sabateeshan Mathavarajah and colleagues from Dalhousie University, Halifax, N.S., examined the sequences of the ACE2 receptors in the various marine mammal species. The ACE2 receptor has recently been identified as the SARS-CoV-2 receptor, which allows for infection.
The researchers examined genomic databases of the marine species to determine if their ACE2 receptor sequences indicated the potential for high, medium, or low susceptibility to infection, as reported in Science of the Total Environment. Database analysis was performed for four groups: Cetacea (whales and dolphins), Pinnepidia (seals), Sirenia (sea cows), and Fissipedia (sea otters and polar bears).
The researchers defined susceptibility values based on comparable binding with the receptor and came up with the following subgroups: higher than human, high (resembles human ACE2), medium (resembles cat ACE2), and low (resembles dog ACE2). It has yet to be established if these marine mammals actually are infected with SARS-CoV-2 and what the impact of such an infection might have on animal health or humans who come in contact with infected animals.
They also cross-referenced for the level of species endangerment and with maps of potential wastewater contamination for certain areas that species came in contact with, using Alaska as the model.
Populations in danger
The researchers found 15 species that are already at risk globally that fall under the categories of near threatened, vulnerable, endangered, and critically endangered that were predicted to be medium to higher susceptibility to the SARS-CoV-2 virus than humans. Cross infection is of particular concern because other coronaviruses have been shown to have severe and lethal effects among many of these species.
Among the potentially impacted species were the near threatened–status Antarctic Mink whale and the stellar sea lion; the vulnerable sperm whale, northern fur seal, and Atlantic walrus; the endangered northern and southern sea otters, the North Pacific right whale, and the Amazon River dolphin; and the critically threatened Baiji and Vaquita dolphin species.
Pollution risks
In Alaska, as of Aug. 7th, 2020, there were 4,221 confirmed cases of COVID-19 and this number continues to rise, according to the researchers. Since there is a diversity of marine mammals in Alaska and their populations are well documented, they compared this information with available data on the wastewater treatment plants in the state. They were thus able to determine the potential geographic locations and species at high risk for transmission of SARS-CoV-2 via wastewater effluent.
Among their findings, the city of Cold Bay discharges wastewater into Cold Bay, where there are Northern sea otter populations that are predicted to be highly susceptible to the virus. Beluga whales are also predicted to have high susceptibility and they can be found in Bristol Bay near Naknek, a city which relies only on lagoon treatment prior to the discharge of wastewater effluent; the city of Dillingham discharges wastewater into the Nushagak River where beluga whales are found. In Palmer, wastewater effluent flows into the Talkeetna River, which is a tributary to the Susitna River and home to two species predicted to have high susceptibility, beluga whales and harbor seals, the authors added.
Based on these results, the researchers predicted that there was likely a significant risk to sea mammals across the globe, especially where less-adequate treatment facilities and high population densities may lead to greater wastewater contamination.
“Given the proximity of marine animals to high-risk environments where viral spill over is likely, we must act with foresight to protect marine mammal species predicted to be at risk and mitigate the environmental impact of the COVID-19 pandemic,” the researchers concluded.
The authors reported that they had no disclosures.
SOURCE: Mathavarajah S et al. Sci Total Environ. 2020 Oct 29. doi: 10.1016/j.scitotenv.2020.143346.