The origins of SARS-CoV-2
What are the origins of SARS-CoV-2?
· There’s irrefutable evidence that SARS-CoV-2 came from a natural source. Coronaviruses are common in humans and animals. They cause cross-species infections by jumping from one host to another.
· And that’s what happened with SARS-CoV-2. It also happened with SARS-CoV and MERS-CoV. Scientists have mapped the genomes of over 70,000 samples (and counting) of SARS-CoV-2 from patients in the United States, China, Europe, Brazil and South Africa. Subsequent genetic analysis has revealed that SARS-CoV-2 is 96% similar to a bat virus, called RaTG13, first sampled from the Yunnan Province of China in 2013. Additional data indicate that SARS-CoV-2 likely circulated, unnoticed, in bats for decades before being identified – divergence dates as early as 1948 have been estimated. Bats are common reservoirs for other coronaviruses known to infect humans, including SARS-CoV and MERS-CoV.
· But how did this virus get from bats to humans? The use of bat guano (or excrement) as fertilizer may have contributed to the spread of disease. Or the tradition of eating rare and unusual wildlife might be behind the outbreak. It is likely that there is an intermediate host for SARS-CoV-2. The receptor binding domain of the SARS-CoV-2 Spike protein is genetically similar to a coronavirus that infects pangolins. So it could be that SARS-CoV-2 jumped from bats, to pangolins, and then to humans.
· Wet markets have historically been tied to the emergence of novel human pathogens. For example, SARS-CoV which also originated in bats, jumped to the palm civet, sold at a wet market in Guangdong, China, where the first human infections were subsequently recorded. And MERS-CoV originated in bats and then jumped to dromedary camels before appearing in humans.
· SARS-CoV-2 is the 7th coronavirus known to infect humans. It belongs to the Sarbecovirus subgenus of the Coronaviridae. Coronaviruses, which are genetically diverse, frequently cause cross-species infections, leading to the periodic natural emergence of novel coronaviruses in humans, as is the case with SARS-CoV-2.