- A new study identifies 15 marine mammal species, including whales, dolphins, seals and sea otters, that could be susceptible to the SARS-CoV-2 virus through contact with wastewater.
- According to the researchers, vulnerable populations of marine animals that congregate near wastewater discharge sites face elevated risks.
- To minimize these risks, the researchers suggest closely monitoring vulnerable populations for possible infection and vaccinating if necessary, and also restricting access to at-risk captive marine mammals.
- However, other experts say it is implausible for marine animals to get sick through contact with wastewater since virus transmission through water is unlikely.
A few months after the first confirmed cases of COVID-19 began to pop up in the U.S., a piece of news came out of the Bronx Zoo in New York City: one of its Malayan tigers (Panthera tigris jacksoni), Nadia, had developed a cough. When a veterinarian tested Nadia for SARS-CoV-2, the virus that causes COVID-19, “out of an abundance of caution,” the test came back positive. According to the zoo, Nadia had likely contracted the virus from an asymptomatic caretaker, making her the first known captive tiger to get the disease. The incident raised a pivotal question: could humans transmit SARS-CoV-2 to other species?
News of Nadia’s illness led Saby Mathavarajah, a researcher at Dalhousie University in Halifax, Canada, to investigate whether marine mammals, such as cetaceans and pinnipeds, could get infected with SARS CoV-2 through wastewater.
“There are no documented cases of SARS-CoV-2 to date in marine mammals but we do know that both dolphins and beluga whales have been infected with related gamma coronaviruses in the past,” Mathavarajah told Mongabay in an email. “Since most marine mammals are social, it is also possible for spread of coronaviruses between animals through close contact. So once one animal is infected it could threaten entire populations.”
In a recent paper, Mathavarajah and colleagues at Dalhousie University found that 15 marine species, including whales, dolphins, seals and sea otters, could be susceptible to SARS CoV-2 due to having a receptor — angiotensin converting enzyme 2 (ACE2) — that allows the virus to infect cells. This research builds upon previous studies that examine the risk of SARS CoV-2 infection across a wide range of vertebrates, including cetaceans.
“By modelling the binding of different ACE2 proteins from different animals using computer simulations, we can predict the strength of binding and thus potential susceptibility of different animals to infection by SARS-CoV-2,” Mathavarajah said. “Using this approach, we found that the key amino acids needed for binding the Spike protein of SARS-CoV-2 were very similar between the human ACE2 and that of several marine mammals, including dolphins, beluga whales, seals and sea otters.”
Some species, such as the endangered Amazon river dolphin (Inia geoffrensis), endangered northern sea otter (Enhydra lutris kenyoni), and vulnerable sperm whale (Physeter macrocephalus), are considered to have a higher possible susceptibility to the virus than humans, according to the study. This is wasn’t the only criteria the research team looked at — they also regarded the conservation status of each species to assess the potential danger of SARS CoV-2.
“Taking this criteria into account, certain populations of beluga in Alaska are highly at-risk,” Mathavarajah said. “However, the white dolphin found in the Yangtze River in Wuhan China, known as the Baiji, is the most at-risk marine mammal in the world for COVID-19. This is especially so, considering the Baiji [Lipotes vexillifer] is believed to be functionally extinct and that the Yangtze River flows through Wuhan Province — the epicentre of the COVID-19 pandemic.”
David Larsen, an epidemiologist and associate professor of public health at Falk College, says the virus’s genetic material, known as its RNA, can enter water through “fecal shedding.”
“COVID-19 appears to be a vascular disease, with some implications in the gastro-intestinal [tract],” Larsen told Mongabay in an email. “About half of people with COVID-19 shed viral RNA in their feces, and so that gets deposited into the wastewater.”
Naomi Rose, a marine mammal scientist for the Animal Welfare Institute, says cetaceans could come into contact with the virus “in areas where the wastewater is discharged and the virus would be transmitted through their mucus membranes,” such as their eyes, blowholes or the insides of their mouths. “It would be like how we get infected in air,” she told Mongabay in an email. However, the likelihood of contracting the virus would depend on the amount of exposure, she added.
According to the study, there may be a greater risk for animals that congregate around wastewater discharge sites. For instance, there are several locations along the south shore of Alaska where wastewater is treated in open lagoons, close to local populations of beluga whales (Delphinapterus leucas).
“Many of these whales are found swimming near the wastewater treatment plant of Anchorage, the largest city in Alaska,” Mathavarajah said. “In this situation, any infective virus present in the effluent has the potential to infect these animals. With many of these marine mammal species being social, the capacity for the virus to spread is not negligible.”
The authors suggest closely monitoring vulnerable marine animal populations for signs of infection, and if the virus is found to have spilled over into any populations, a vaccination program could be a solution. “[I]t is not far-fetched to imagine that wild populations affected by the virus, just like humans, can be protected by herd immunity through vaccination,” they write in the study.
But Larsen, who recently published a study on wastewater surveillance of COVID-19, says the risk of infection via water is “possible, but very implausible.”
“We don’t expect transmission to occur within water,” he said. “The idea of marine mammals getting COVID-19 is pretty far-fetched.”
Rose says there’s perhaps a bigger concern for captive cetaceans that would be “in close contact with people who may be asymptomatically infected by SARS CoV-2.”
“Certainly the risk is there — and this is most likely to create problems for captive wildlife interacting with infected caretakers or the public, not free-roaming wildlife,” she said.
Mathavarajah and his colleagues also identified the potential danger to captive marine mammals, and have suggested limiting access to at-risk species in marine parks and other facilities.
According to Rose, the value of this study, as well as other studies that examine the risk of SARS CoV-2 infection in non-human animals, lies in its demonstration of how easily diseases can be spread through zoonosis, as well as reverse zoonosis.
“[D]iseases may start jumping from wildlife to humans and vice versa in the future, more and more,” Rose said. “We need to be aware of this possibility and mitigate the risk — rather than continue on as we have, assuming animal diseases aren’t our problem and vice versa.”
Citations:
Damas, J., Hughes, G. M., Keough, K. C., Painter, C. A., Persky, N. S., Corbo, M., … Lewin, H. A. (2020). Broad host range of SARS-Cov-2 predicted by comparative and structural analysis of ACE2 in vertebrates. Proceedings of the National Academy of Sciences, 117(36), 22311-22322. doi:10.1101/2020.04.16.045302
Larsen, D. A., & Wigginton, K. R. (2020). Tracking COVID-19 with wastewater. Nature Biotechnology, 38(10), 1151-1153. doi:10.1038/s41587-020-0690-1
Mathavarajah, S., Stoddart, A. K., Gagnon, G. A., & Dellaire, G. (2020). Pandemic danger to the deep: The risk of marine mammals contracting SARS-Cov-2 from wastewater. Science of the Total Environment. doi:10.1101/2020.08.13.249904
Banner image caption: A flotilla of killer whales or Orca on review. Image courtesy of Dr. Brandon Southall, NMFS/OPR / NOAA.
Elizabeth Claire Alberts is a staff writer for Mongabay. Follow her on Twitter @ECAlberts.
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