Swine acute diarrhea syndrome coronavirus replication in primary human cells reveals potential susceptibility to infection.

Zoonotic coronaviruses represent an ongoing threat, yet the myriads of circulating animal viruses complicate the identification of higher-risk isolates that threaten human health. Swine acute diarrhea syndrome coronavirus (SADS-CoV) is a newly discovered, highly pathogenic virus that likely evolved from closely related HKU2 bat coronaviruses, circulating in Rhinolophus spp. bats in China and elsewhere. As coronaviruses cause severe economic losses in the pork industry and swine are key intermediate hosts of human disease outbreaks, we synthetically resurrected a recombinant virus (rSADS-CoV) as well as a derivative encoding tomato red fluorescent protein (tRFP) in place of ORF3. rSADS-CoV replicated efficiently in a variety of continuous animal and primate cell lines, including human liver and rectal carcinoma cell lines. Of concern, rSADS-CoV also replicated efficiently in several different primary human lung cell types, as well as primary human intestinal cells. rSADS-CoV did not use human coronavirus ACE-2, DPP4, or CD13 receptors for docking and entry. Contemporary human donor sera neutralized the group I human coronavirus NL63, but not rSADS-CoV, suggesting limited human group I coronavirus cross protective herd immunity. Importantly, remdesivir, a broad-spectrum nucleoside analog that is effective against other group 1 and 2 coronaviruses, efficiently blocked rSADS-CoV replication in vitro. rSADS-CoV demonstrated little, if any, replicative capacity in either immune-competent or immunodeficient mice, indicating a critical need for improved animal models. Efficient growth in primary human lung and intestinal cells implicate SADS-CoV as a potential higher-risk emerging coronavirus pathogen that could negatively impact the global economy and human health.

Attenuation of a virulent swine acute diarrhea syndrome coronavirus strain via cell culture passage.

Swine acute diarrhea syndrome coronavirus (SADS-CoV) is a newly identified enteric alphacoronavirus that causes fatal diarrhea in newborn piglets in China. Here, we propagated a virulent strain SADS-CoV/CN/GDWT/2017 in Vero cells for up to 83 passages. Four strains of SADS-CoV/GDWT-P7, -P18, -P48 and -P83 were isolated and characterized. Sequence alignments showed that these four novel strains exhibited 16 nucleotide mutations and resultant 10 amino acid substitutions in open reading frame 1a/1b, spike, NS3a, envelope, membrane and nucleocapsid proteins. Furthermore, a 58-bp deletion in NS7a/7b was found in P48 and P83 strains, which led to the loss of NS7b and 38 amino acid changes of NS7a. Pig infection studies showed that the P7 strain caused typical watery diarrhea, while the P83 strain induced none-to-mild, delayed and transient diarrhea. This is the first report on cell adaption of a virulent SADS-CoV strain, which gives information on the potential virulence determinants of SADS-CoV.