Maybe, Covid-19 found most powerful habitat as oceans and marine animals of oceans as intermediate hosts. If so that is why viruses accumulate in ocean waters as so much and by evaporation they pass to atmospheric air and dispersed all over the world by winds and probably also by rain and snow ? ? ?
COVID-19 seems not to be very different from SARS regarding its clinical features; it seems to be less lethal than MERS, which is less closely related to the other two coronavirus in terms of both phylogenetic and pathogenetic features.
COVID-19 generally has a less severe clinical picture, and thus it can spread in the community more easily than MERS and SARS, which have frequently been reported in the nosocomial setting.
SARS-CoV-2, SARS-CoV and MERS-CoV use receptors that have been found in both the upper and the lower respiratory tract. Moreover, other human coronaviruses, such as NL63-CoV, cause a mild illness even if they bind to the same receptor as SARS-CoV-2 and SARS-CoV ]. So, in our opinion, it is likely that the different inoculum dose at the time of infection makes the difference in terms of severity of the disease; heavy inoculum exposures seem to be linked to a greater penetration into the lower respiratory tract, causing severe pneumonia, whereas lower inoculum exposures allow viruses to only reach the upper airway, causing a milder infection.
Viral loads are higher at the time of symptom onset and are higher in nose than in throat specimens . Furthermore, in patients affected by COVID-19, viral load progressively decreases within days, following a different pattern from SARS in which the highest shedding is recorded after 10 days from symptom onset . These findings suggest that SARS-CoV-2 may spread more easily in the community than SARS even when initial mild symptoms or no symptoms are present.
The differences in the intrinsic virulence of the viruses themselves can explain the different capacity for spreading. MERS-CoV has a higher mortality but a lower transmissibility, probably because it causes a more severe clinical picture than COVID-19 and SARS, requiring hospitalization more frequently, thus reducing the community spread of the infection and increasing the nosocomial transmission . On the other hand, the apparent higher mortality of MERS could be biased by the fact that most of the data available on MERS were derived from hospitalized patients, thus implicating a more severe clinical picture than community-acquired cases .
Interestingly, despite the high virological similarity between the SARS-CoV-2 and SARS-CoV, gastrointestinal symptoms and diarrhoea seem to be much more common in SARS, although the proportion of SARS patients with gastrointestinal symptoms varies among different studies. The gastrointestinal route of transmission has also been hypothesized for MERS-CoV through the consumption of infected camel milk; moreover, gastrointestinal transmission has been demonstrated in the animal model through intestinal DPP4 receptors . SARS-CoV replicates in the enteric epithelium by binding to the ACE2 receptor, and it cannot be excluded that SARS-CoV-2 would behave in the same way . This may contribute to the hypothesis that SARS-CoV-2 could also be transmitted via this route; there is also evidence that SARS-CoV and MERS-CoV remain viable in environmental conditions that could facilitate faecal–oral transmission .
One reason is, Coronaviruses are the type of viruses which has RNA genome, RNA viruses lack exonuclease activity, so hence no oroofreading and their genome may become very lethal or vice versa in its mutation result. Habitat may favor its mutation rate lil bit, environmntal factors may mutate the genome, no oroof reading and hence even the genotype changes
Sinan Ibaguner This is a very strange way to look at infection and transmission routes. Your weird hyptheses are not at all supported by any evidence.
Dear Prof Christian G Meyer : Will you please read websites down below whether coronavirus can be available in oceans without being denatured. Thank you for your comments.
https://en.wikipedia.org/wiki/Human_viruses_in_water
https://en.wikipedia.org/wiki/Marine_viruses
https://en.wikipedia.org/wiki/Sea_snot
https://www.futurity.org/millions-of-marine-viruses-ebb-and-flow/
https://bionumbers.hms.harvard.edu/bionumber.aspx?id=113291&ver=2