SARS-CoV originated from bats in 1998 and may still exist in humans

TL;DR

This study traces the origin of human SARS-CoV to bats in 1991, details its evolution into virulent and weakly virulent strains, and suggests that undetected strains may still circulate in humans, posing reemergence risks.

Contribution

It provides new evidence that SARS-CoV originated directly from bats in 1991 and evolved into different strains, highlighting ongoing risks of reemergence.

Findings

Human SARS-CoV originated from bats in 1991

Virulent and weakly virulent strains co-exist in humans

Seropositivity detected in children born after 2005

Abstract

SARS-CoV is believed to originate from civets and was thought to have been eliminated as a threat after the 2003 outbreak. Here, we show that human SARS-CoV (huSARS-CoV) originated directly from bats, rather than civets, by a cross-species jump in 1991, and formed a human-adapted strain in 1998. Since then huSARS-CoV has evolved further into highly virulent strains with genotype T and a 29-nt deletion mutation, and weakly virulent strains with genotype C but without the 29-nt deletion. The former can cause pneumonia in humans and could be the major causative pathogen of the SARS outbreak, whereas the latter might not cause pneumonia in humans, but evolved the ability to co-utilize civet ACE2 as an entry receptor, leading to interspecies transmission between humans and civets. Three crucial time points - 1991, for the cross-species jump from bats to humans; 1998, for the formation of the human-adapted SARS-CoV; and 2003, when there was an outbreak of SARS in humans - were found to associate with anomalously low annual precipitation and high temperatures in Guangdong. Anti-SARS-CoV sero-positivity was detected in 20% of all the samples tested from Guangzhou children who were born after 2005, suggesting that weakly virulent huSARS-CoVs might still exist in humans. These existing but undetected SARS-CoVs have a large potential to evolve into highly virulent strains when favorable climate conditions occur, highlighting a potential risk for the reemergence of SARS.