Is COVID-19 a Potential Threat to Marine Mammal Populations?

COVID-19, caused by the novel coronavirus SARS-CoV-2¹, was declared a global pandemic on March 11, 2020². The impacts of COVID-19 have been devastating and far-reaching; health care systems are overwhelmed, country-wide lockdowns have been imposed, borders have been closed, and many industries have been severely affected. With over 59 million confirmed cases worldwide³, COVID-19 is a real and unprecedented threat to human beings throughout the globe.

But could COVID-19 also be a threat to marine mammal populations?  Some scientists say it’s a possibility. 

The transmission of COVID-19 to terrestrial mammal species in proximity to humans has already occurred.  At the Bronx Zoo in New York, several large cats were infected with the SARS-CoV-2 virus.  Mink kept in large numbers on mink farms have caught the virus from infected workers, resulting in the culling of millions of animals in the Netherlands, Denmark, Spain, Sweden, Italy, and the United States. While there are no documented cases of COVID-19 infection in marine mammals⁴, some researchers are concerned that the SARS-CoV-2 virus could be transmitted to marine mammal populations living in coastal areas through wastewater runoff⁴.  COVID-19 patients shed the virus in their stool and urine⁵, and the virus has been detected in marine areas throughout the world with untreated wastewater⁶.

In order to determine the susceptibility of marine mammals to the SARS-CoV-2 virus, researchers at Dalhousie University in Halifax examined a particular protein, called angiotension-converting enzyme 2 (ACE2), found on the surface of many cells in an animal’s body.  ACE2 acts as a “cellular doorway” for the SARS-CoV-2 virus.  The virus binds to an animal’s ACE2 receptors, much like a key in a lock.  Variations in the ACE2 receptors of different species determine how well the virus’s spike protein can bind to the cell surface, and this binding efficiency dictates how easily the virus can penetrate an animal’s cells⁷.  Researchers examined how ACE2 variations in marine mammals could make some species susceptible to infection by the SARS-CoV-2 virus.

The results are concerning.  The majority of cetacean (whale, dolphin, and porpoise) species have variations in their ACE2 receptors that make them even more susceptible to the SARS-CoV-2 virus than humans⁴.  Many pinniped (seal and sea lion) species, as well as Northern sea otters, are also predicted to be highly susceptible⁴.  More than half of the species predicted to be susceptible to the virus are already at risk of extinction.

The study uses Alaska as an example of an area where COVID-19 could be transmitted to vulnerable marine mammal populations.  In some areas, Alaska’s wastewater treatment system is not sufficient for removing all virus particles⁸.  The study identifies some high-risk areas where insufficient wastewater treatment occurs in the vicinity of marine mammals, including an area that is frequented by the endangered Cook Inlet beluga population⁴.  Populations of Northern sea otters, walruses, and harbour seals were also determined to be at risk⁴.  While the effect of the SARS-CoV-2 virus on marine mammals is not known, infections with other coronaviruses can lead to necrosis of the liver in beluga whales and of the lungs in harbour seals^9,10.

But is wastewater runoff a viable route of transmission for the SARS-CoV-2 virus?

Some experts think that it’s highly unlikely; studies have shown that coronavirus particles are likely to experience a significant loss of infectivity in aquatic habitats due to dilution and exposure to UV radiation¹¹.  But other researchers argue that the risk cannot be ruled out.  The SARS-CoV-2 virus is sturdy, and has proven to be far more stable in the environment than predicted⁸.  The high binding efficiency of ACE2 receptors to the SARS-CoV-2 virus for some marine mammals means that they would not need to be exposed to high concentrations of the virus to become infected⁴.  Much like humans, many species of marine mammals are highly social, so the virus could have the potential to spread quickly through these populations if one animal were infected⁴.

It would not be the first time that a terrestrial pathogen has infected marine mammals; Toxoplasma gondii, a protozoan that causes toxoplasmosis in cats, infected a threatened population of sea otters in California.  A population of elephant seals off the coast of California were infected with the H1N1 virus-the virus responsible for the swine flu outbreak in 2009.  It is thought that animals were exposed to the virus via human excrement discharged into the water by shipping vessels in the area¹².  The same H1N1 virus was then transmitted to Northern sea otters, who were likely infected after being in proximity to elephant seals¹².

While it remains to be seen if COVID-19 will infect marine mammal populations, the current global pandemic is having an indirect impact on marine mammal populations.

As highlighted in our Ocean Watch Spotlight report, the negative consequences of the pandemic include increased exposure to plastic pollution due to the rising demand for single use items and personal protective equipment, as well as the decreased ability to respond to marine mammal incidents and monitor cetacean populations.  Cetacean sightings reported to the BC Cetacean Sightings Network (BCCSN) during the pandemic are almost halved compared to the same period in 2019.  These reports provide valuable information about species distribution and abundance and provide real-time information for the WhaleReport Alert System (WRAS) to help prevent ship strikes and disturbance.

The study highlights the importance of identifying high risk areas where viral spillover may impact susceptible wildlife.  The assessment and appropriate treatment of wastewater in these high-risk areas is a key factor in reducing the transmission of the SARS-CoV-2 virus and other pathogens into our marine environment.  The potential effects (both direct and indirect) of COVID-19 on marine mammal populations emphasizes the need for monitoring technologies-such as the use of drones to collect cetacean blow samples and assess body condition-to detect any outbreaks in marine mammal populations.

References

1. World Health Organization. Naming the coronavirus disease (COVID-19) and the virus that causes it [Internet]. 2020 [cited 2020 May 22]. Available from: https://www.who.int/emergencies/diseases/novel-coronavirus-2019/technical-guidance/naming-the-coronavirus-disease-(covid-2019)-and-the-virus-that-causes-it
2. Cucinotta D, and Vanelli M. (2020). WHO Declares COVID-19 a Pandemic. Acta Biomed. 91:157–60.
3. World Health Organization. WHO Coronavirus Disease (COVID-19) Dashboard. 2020 [Internet]. 2020 [cited 2020 Nov 16]. Available from: https://covid19.who.int/?gclid=EAIaIQobChMIs6bQi_eH7QIVIRxlCh1iFAgmEAAYASAAEgJLD_D_BwE
4. Mathavarajah S., Stoddart, A.K., Gagnon, G.A. et al. Pandemic danger to the deep: The risk of marine mammals contracting SARS-CoV-2 from wastewater. Science of the Total Environment. https://doi.org/10.1016/j.scitotenv.2020.143346
5. Sun, J., Zhu, A., Li, H., Zheng, K., Zhuang, Z., Chen, Z., and Li, Y.M. (2020). Isolation of infectious SARS-CoV-2 from urine of a COVID-19 patient. Emerg Microbes Infect 9 (1), 991–993. https://doi.org/10.1080/22221751.2020.1760144.
6. Ahmed, W., Angel, N., Edson, J., Bibby, K., Bivins, A., O’Brien, J.W., and Mueller, J.F. (2020). First confirmed detection of SARS-CoV-2 in untreated wastewater in Australia: A proof of concept for the wastewater surveillance of COVID-19 in the community. Sci Total Environment 728, 138764. https://doi.org/10.1016/j.scitotenv.2020.138764.
7. Mathavarajah, S. and Dellaire, G. (2020). Lions, tigers and kittens too: ACE2 and susceptibility to COVID-19. Evolution, Medicine, and Public Health, 101-113. https://doi.org/10.1093/emph/eoaa021
8. Aboubakr, H.A., Sharafeldin, T.A., and Goyal, S.M. (2020). Stability of SARS-CoV-2 and other coronaviruses in the environment and on common touch surfaces and the influence of climatic conditions: a review. Transbound. Emerg. Dis. https://doi.org/10.1111/tbed.13707.
9. Mihindukulasuriya, K.A., Wu, G., St Leger, J., Nordhausen, R.W., Wang, D., 2008. Identification of a novel coronavirus from a beluga whale by using a panviral microarray. J. Virol 82 (10), 5084–5088. https://doi.org/10.1128/JVI.02722-07.
10. Woo, P.C., Lau, S.K., Lam, C.S., Tsang, A.K., Hui, S.W., Fan, R.Y., and Yuen, K.Y. (2014). Discovery of a novel bottlenose dolphin coronavirus reveals a distinct species of marine mam-mal coronavirus in Gammacoronavirus. J Virol 88 (2), 1318–1331. https://doi.org/10.1128/JVI.02351-13.
11. Mordecai, G. J. and Hewson, I. (2020). Coronaviruses in the sea. Frontiers in Microbiology 11, 6pp. https://doi.org/10.3389/fmicb.2020.01795
12. Goldstein, T., Mena, I., Anthony, S.J., Medina, R., Robinson, P.W., Greig, D.J., and Boyce, W.M. (2013). Pandemic H1N1 influenza isolated from free-ranging Northern Elephant Seals in 2010 off the central California coast. PLoS One 8 (5), e62259.https://doi.org/10.1371/journal.pone.0062259.