Coronavirus News: Researchers Caution That Aquatic Animals Could Be Potential Reservoirs For SARS-CoV-2 And Prospective Therapeutics From Algae
: Researchers from the Department of Hydrobiology at the Institute of DACBiol at the Universidad Juárez Autónoma de Tabasco-Mexico are warning that careful attention and monitoring needs to be paid to the aquatic life forms and water life as they could be potential impacts from the current COVID-19 pandemic.
The researchers expressed their concerns and study findings from analysis of past studies in a paper published on a preprint server and are currently being peer-reviewed. https://www.preprints.org/manuscript/202009.0198/v1
Already studies have shown that the SARS-CoV-2 coronavirus can survive in water and are being found in waste-waters coupled with the fact that certain aquatic mammals and fishes can be infected by the virus. Several studies have demonstrated the presence of SARS-CoV-2 in sewage from infected areas, and the virus persists for weeks in infectious form.
Most coronaviruses are known to infect humans, bats, camels, and birds, all of which are terrestrial species. However, as part of the order Nidovirales, they can infect crustaceans, fish, and marine mammals as well, many of which are commercially important.
Past studies have shown that the alpha-, beta-, gamma- and delta-coronaviruses infect the respiratory tract in both humans and non-humans and the gut in other organisms. This includes the betaCoVs SARS-CoV and MERS-CoV (Middle East Respiratory Syndrome). These two are zoonotic viruses, with animal reservoirs. The coronavirus also includes another subfamily containing two genera, Toro- and Bafini-virus, which have been found in Teleosts.
Past studies have shown that over a hundred pathogenic viruses have been found to be shed in human and animal feces, and thence to water bodies. This can lead to feco-oral transmission, allowing them to infect the digestive system and perpetuating the transmission chain. In fact, it is thought that 10 billion viruses may be present in a gram of feces.
These infective viruses can enter free-living organisms in the water and be transmitted to humans, triggering new outbreaks. This risk must be evaluated, stressed the researchers.
Importantly water-borne transmission is known to occur with alpha- and beta-CoVs, and the contaminated water may come into contact with the new host via swallowing, breathing of aerosolized droplets, through the skin or mucosal membranes, or aspiration into the lungs. CoVs are present in only minute concentrations in natural aquatic bodies, however.
It is known through past studies that crustaceans also called shellfish, may harbor the virus in their exoskeleton. Still, since this is typically removed before eating, they have not been identified as potential agents of transmission to humans. Shrimps in Southeast and East Asia may harbor the yellow head virus.
Interestingly, the first Bafinivirus was found in white bream, but some Bafiniviruses colonize certain fish, such as the common carp, or the salmon, or bighead face fish. They have caused 70% mortality in fish farms, due to liver and kidney damage, with bleeding from the skin and into the abdomen. However, these are typically found in the gut of the host.
Also, since the SARS-CoV-2 coronavirus can tolerate a broader range of temperatures than earlier thought, between 4 to 20 degrees Celsius in the air, it can live and replicate within fish, especially since they are ectothermic creatures with body temperature equalizing with the environment. Many such fish hosts have an adaptable body temperature. And the infection of marine mammals and Peneid shrimps that have a tropical habitat seems to indicate that this would not restrict future infection with the virus in these marine and aquatic creatures.
Significantly, waterfowl seem to harbor the widest range of coronaviruses, about 96 varieties, if not more, from gamma- and delta-CoVs. Among the many waterfowl that feed with aquatic environments, ducks appear to be the group with the higher diversity. Some migratory birds have an expansive habitat and could, in theory, spread the virus effectively over a vast area. Research is required to explore the potential for CoV infection and transmission in these species.
Marine mammals such as seals in a Florida aquarium are known to have died of coronavirus-induced hemorrhagic pneumonia half a century ago, called the HSCoV (Harbor Seal coronavirus) outbreak. Other CoV infections in these species have involved viral bronchitis in beluga whales and bottlenose dolphins, both of which live in groups promoting viral spread. Thus, monitoring is essential to maintain the health of these species and to prevent onward transmission to other wild species, as well as to humans who come into contact with these animals in water parks or aquariums, in food markets, and when working with them in the wild.
Although there is no literature on the actual spread of aquatic coronaviruses to humans, respiratory viruses have been carried to humans from wild or captive animals, as in the H7N7 flu virus, which infected people via an autopsy of a seal, or through aerosols from a captive sneezing seal. The outcome, however, was conjunctivitis, rather than flu or respiratory disease.
Although many other viral infections have been detected in shellfish, involving human enteric viruses like hepatitis A virus, norovirus, rotavirus, and enterovirus, CoV outbreaks have not been recorded. H5N1 and A1 avian influenza viruses are associated with birds and are very contagious, spreading through infected duck meat and blood to humans. Ducks being very susceptible to CoVs, careful monitoring is required to make sure the same does not happen with these pathogens.
Meanwhile In the absence of scientifically documented spread of SARSC-CoV-2 through aquatic organisms, the World Health Organization (WHO) and other health organizations have advised that wild animal markets should be avoided, while also ensuring that contact with farmed animals should be with due precautions. Meanwhile, further studies will occur to understand the effects of mutations and other genetic adaptations on changing routes of transmission between humans and animals, and the emergence of natural reservoirs.
The study team stresses, “The diversity and presence of CoVs in aquatic organisms should be monitored to understand their infectious potential better and avoid future outbreaks in the wild, which eventually could also reach humans.”
On another aspect of the study, the researchers say that certain aquatic organisms, such as seaweed or sponges, could play a key role in the treatment of coronavirus infections. It has been observed through laboratory tests with Halimeda tuna algae, a natural product known as diterpene aldehyde or halitunal found in the algae has anti-coronavirus properties. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7147892/
Also the sponge Mycale sp, which produces a substance called micalamide A, has antiviral capacity against the A59- 241 coronavirus of murine or rodent origins. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7125756/
More interesting is the Axinella corrugata sponge that produces a compound called ethyl ester of esculetin-4-carboxylic acid that has antiviral effects against SARS-CoV. https://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532007000200030
These substances together with other products of natural origin could be studied as possible therapeutics against the SARS-CoV-2 in the future. https://pubmed.ncbi.nlm.nih.gov/32248575/
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