SARS-CoV-2 Virus – where did it come from and where did it evolve?
The European Centre for Disease Prevention and Control discusses that a meta-analysis of different estimates of the time to the last common ancestor of the virus indicate that the pandemic started sometime between 6 October and 11 December 2019.
The original animal reservoir of the virus was most likely bats, and an intermediate animal host could have been involved in the transmission to humans. From the genomic evidence, it is unlikely that the virus is a product of in vitro manipulation, pathogen in cell culture, or that it is of synthetic origin. There is currently very limited evidence that any of the mutations accumulated since the introduction of the SARS-CoV-2 virus in the human population have any effect on disease characteristics or transmissibility.
SARS-CoV-2 and Seasonality
Analyses of the early phase of the pandemic suggested that temperature, and relative and absolute humidity were associated with transmission intensity of SARS-CoV-2. These studies suggested that cold and dry weather conditions could favour the transmission of SARS-CoV-2.
SARS-CoV-2 might display seasonal patterns similar to those of other human coronaviruses with peak incidence in winter months. However, it remains to be seen if weather factors, such as higher temperature, higher humidity or more ultraviolet, will suppress the transmissibility during summer months in temperate regions of the northern hemisphere. Modelling suggests that any possible decrease during the summer would not prevent substantial outbreaks if no control measures were in place.
Population immunity might be a more important determinant of transmission while climate would affect the timing and extent of transmission, at least at the early phase of the pandemic. Once the virus is established in human populations, climatic factors will influence the seasonality of endemic cycles by latitude.
SARS-CoV-2 and its Survival in the Environment
Recent publications have evaluated the survival of SARS-CoV-2 on different surfaces. These include the environmental stability of viable SARS-CoV-2 is:
- Up to three hours in the air post aerosolisation
- Up to four hours on copper
- Up to 24 hours on cardboard
- Up to 2 to 3 days on plastic and stainless steel, albeit with significantly decreased titres.
The virus has been shown to be more stable on smooth surfaces, with detection of infective virus on surgical mask material for up to seven days.
Interestingly no infectious virus could be detected after five minute incubation at room temperature in contact with usual disinfectants such as household bleach or 70% ethanol etc. However, it was detectable with the use of hand soap after five-minute incubation.
Currently there is no data on the survival of SARS-CoV-2 in sea water, but a dilution effect will contribute to decreasing viral load and salinity may contribute to viral inactivation.
The viable of the virus is expected to be higher in untreated waters of rivers, lakes and freshwater pools.
This is in comparison to survival in swimming pools and the sea as the presence of viral inhibitors such as salinity and chlorine is less expected and if present the concentration is expected to be lower.
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