BREAKING! Researchers Warn That SARS-CoV-2 Could Also Infect Aquatic Mammals Such As Dolphins And Whales, Creating New Viral Reservoirs!
Italian researchers have in a new study found that cetaceans which include aquatic mammals such as whales, dolphins, and porpoises could also become infected with the SARS-CoV-2 virus and could also end up as potential viral reservoirs.
As a result of such 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).
Furthermore, 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, the study team 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.
Although no SARS-CoV-2 positivity was found in samples analyzed for the survey, 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.
Interestingly a 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.
The study findings were published in the peer reviewed journal: Pathogens.
This study however only focused on stranded cetaceans found dead along the Italian coast. The National Reference Centre for Diagnostic Investigations on Stranded Marine Mammals, in collaboration with the Istituti Zooprofilattici Sperimentali, screened these stranded aquatic mammals along the Italian coast between 2020 and 2022 for SARS-CoV-2.
The COVID-19 disease, which arises from infection with the SARS-CoV-2 coronavirus, has caused over 6.55 million deaths worldwide. In addition to infecting humans, SARS-CoV-2 can potentially infect various types of wild mammals.
Already SARS-CoV-2 has been found to infect and replicate in ferrets, cats, rabbits, and farmed mink. In farmed mink, spillover events occurred involving farm workers in Poland and the Netherlands.
SARS-CoV-2 infections were identified in other mammals; however, most wild animals do not appear to have a significant role in the current spread of SARS-CoV-2 among humans, albeit pet hamsters that have demonstrated the possibility
of zoonotic spread.
However, the circulation of SARS-CoV-2 in animals could promote the emergence of new variants while also putting them at risk.
It was found that similar as in humans, SARS-CoV-2 infection in animals can lead to pneumonia, causing the animals could die, thus affecting wildlife conservation efforts.
Such an impact on wildlife has been reported with the cetacean morbillivirus (CeMV), which has caused large numbers of deaths among cetaceans.
Corresponding author, Dr Cristina Casalone from the Scientific and technical office of REMESA Istituto Zooprofilattico Sperimentale della Sicilia told Thailand Medical News
, “As a result of cetaceans having homologous angiotensin-converting enzyme 2 (ACE2) receptors to those in humans, they are considered potentially susceptible to infection with SARS-CoV-2, especially given the broad host range of this virus.”
To date however, there is no evidence of such reverse zoonosis.
It is already known that wastewater contaminated with SARS-CoV-2 could carry the virus to susceptible cetaceans and other species in the aquatic environment, depending on the temperature, humidity, type of water treatment, presence of other microbes, and effects of ultraviolet light and chemicals. With high viral titers, SARS-CoV-2 may survive, especially in the cold, for over 20 days at 4 degrees Celsius or one week at 22 degrees Celsius.
Hence, cetaceans may also act as a natural reservoir for zoonotic microbes, thereby making surveillance for SARS-CoV-2 essential in the case of stranded cetaceans.
More detailed studies and research are needed to understand how such infections affect these mammals, what symptoms occur, whether ACE2 on cetacean macrophages mirrors that in human immune cells, and whether these cells become decoys, or 'Trojan horses,' for the SARS-CoV-2, thus enabling it to enter the lung parenchyma and anchor itself there.
Interestingly, the presence of specific antibodies against SARS-CoV-2 from 61 lung tissue specimens and 25 swabs was reported.
ACE2 receptor expression remained intact, irrespective of age, gender, and species. However, the origin of the cetacean, whether wild or captive, did show a small association.
The study team noted that the current study was small; therefore, research on a larger scale is essential to confirm these associations.
The study team also assessed the presence of ACE2 in lung samples from four animals belonging to S. coeruleoalba and T. truncatus associated with the activation of CD68 macrophages. This experiment aimed to explore the degree of ACE2 expression on inflammatory cells infiltrating the lungs.
The findings showed that the pulmonary intravascular macrophage (PIM) that engulfs and phagocytizes foreign particles is found in blood, while alveolar macrophages reside in the lungs. ACE2 and CD68 molecules were found on cells only in animals exhibiting infection caused by various microbes.
The study team warned that marine cetaceans must be closely monitored to prevent a resurgence of SARS-CoV-2 and further transmission to endangered species living near humans.
Though ACE2 expression did not vary in these cetaceans by age or sex, captive cetaceans showed a higher level of expression. This could be due to their higher stress level, resulting in higher cortisol levels.
Another reason for this observation could also be related to the drugs used to treat captive animals. However, more extensive studies in the future are needed to confirm this association.
The study also emphasized the critical role of neutrophils and macrophages in the innate immune-inflammatory response to SARS-CoV-2. The co-localization of ACE2 with CD68 at higher levels in infected lung tissue, likely on activated type 1 macrophages (M1), may indicate that both alveolar and PIM macrophages are in the frontline of defense against SARS-CoV-2 and may be immediate targets of the virus.
The study team added, “From a One Health perspective, monitoring stranded specimens for systematic surveillance of SARS-CoV-2 infection in marine mammals is essential to protect human health and that of endangered marine mammal species.”
At present, 23 species of animals from 36 countries are capable of being infected by SARS-CoV-2, which has led to nearly 680 outbreaks among animals. As a result, scientists fear the potential for spillover events into humans and their potential to cause new pandemics in the future.
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