Where's the Virus's 'Missing Link'? We're Still Looking

We may never know exactly how the novel coronavirus, originating in bats, jumped into people. But it's likely that it was passed through another species, which is why the World Health Organization is calling for higher safety standards in the wild animal trade. Health experts have long associated the trade in wild animals with species-to-species disease transmission, reports the BBC. SARS-CoV (which causes SARS), for instance, originated in bats but reached humans through civet cats sold in live-animal markets in China. "Mixing large numbers of species under poor hygienic and welfare conditions, and [with] species that wouldn't normally come close together, gives opportunities for pathogens to jump species to species," says Andrew Cunningham of the Zoological Society of London. "We've actually been expecting something like this to happen for a while."

A study, not yet peer reviewed, suggests the lineage of SARS-CoV-2 (the virus that causes COVID-19) separated centuries ago from that of SARS-CoV. The novel coronavirus shares 96% of its genetic material with its closest known relative, RaTG13, a virus found in bats in a cave in Yunnan, China, reports Nature. But RaTG13, believed to have split off 40 to 70 years ago, is missing the receptor-binding domain that makes SARS-CoV-2 so successful in penetrating humans. A coronavirus found in pangolins is 90% genetically similar to SARS-CoV-2 and has an almost identical receptor-binding domain, but it's thought to have split from the SARS-CoV-2 lineage 140 years ago, according to researchers. A variety of animals are sold at the Wuhan wildlife market, around which SARS-CoV-2 cases first appeared, but an animal with the virus was not found there. (One theory suggests the virus has been present in humans for years.)