SARS-CoV-2 Omicron (B.1.1.529) infection in rhesus macaques, hamsters, and BALB/c mice with severe lung histopathological damage.

Since the first SARS-CoV-2 outbreak in late 2019, the SARS-CoV-2 genome has harbored multiple mutations, especially spike protein mutations. The currently fast-spreading Omicron variant that manifests without symptoms or with upper respiratory diseases has been recognized as a serious global public health problem. However, its pathological mechanism is largely unknown. In this work, rhesus macaques, hamsters, and BALB/C mice were employed as animal models to explore the pathogenesis of Omicron (B.1.1.529). Notably, Omicron (B.1.1.529) infected the nasal turbinates, tracheae, bronchi, and lungs of hamsters and BALB/C mice with higher viral loads than in those of rhesus macaques. Severe histopathological damage and inflammatory responses were observed in the lungs of Omicron (B.1.1.529)-infected animals. In addition, viral replication was found in multiple extrapulmonary organs. Results indicated that hamsters and BALB/c mice are potential animal models for studies on the development of drugs/vaccines and therapies for Omicron (B.1.1.529).

The Gastrointestinal Tract Is an Alternative Route for SARS-CoV-2 Infection in a Nonhuman Primate Model.

BACKGROUND & AIMS: Gastrointestinal (GI) manifestations have been increasingly reported in patients with coronavirus disease 2019 (COVID-19). However, the roles of the GI tract in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection are not fully understood. We investigated how the GI tract is involved in SARS-CoV-2 infection to elucidate the pathogenesis of COVID-19. METHODS: Our previously established nonhuman primate (NHP) model of COVID-19 was modified in this study to test our hypothesis. Rhesus monkeys were infected with an intragastric or intranasal challenge with SARS-CoV-2. Clinical signs were recorded after infection. Viral genomic RNA was quantified by quantitative reverse transcription polymerase chain reaction. Host responses to SARS-CoV-2 infection were evaluated by examining inflammatory cytokines, macrophages, histopathology, and mucin barrier integrity. RESULTS: Intranasal inoculation with SARS-CoV-2 led to infections and pathologic changes not only in respiratory tissues but also in digestive tissues. Expectedly, intragastric inoculation with SARS-CoV-2 resulted in the productive infection of digestive tissues and inflammation in both the lung and digestive tissues. Inflammatory cytokines were induced by both types of inoculation with SARS-CoV-2, consistent with the increased expression of CD68. Immunohistochemistry and Alcian blue/periodic acid-Schiff staining showed decreased Ki67, increased cleaved caspase 3, and decreased numbers of mucin-containing goblet cells, suggesting that the inflammation induced by these 2 types of inoculation with SARS-CoV-2 impaired the GI barrier and caused severe infections. CONCLUSIONS: Both intranasal and intragastric inoculation with SARS-CoV-2 caused pneumonia and GI dysfunction in our rhesus monkey model. Inflammatory cytokines are possible connections for the pathogenesis of SARS-CoV-2 between the respiratory and digestive systems.

Response of the gut microbiota during the Clostridioides difficile infection in tree shrews mimics those in humans.

BACKGROUND: Clostridioides difficile is a major cause of antibiotic associated diarrhea. Several animal models are used to study C. difficile infection (CDI). The tree shrew has recently been developed as a model of primate processes. C. difficile infection has not been examined in tree shrews. We infected tree shrews with hyper-virulent C. difficile strains and examined the alterations in gut microbiota using 16S rRNA gene sequencing. RESULTS: C. difficile colonized the gastrointestinal tract of tree shrew and caused diarrhea and weight loss. Histopathologic examination indicated structures and mucosal cell destruction in ileal and colonic tissues. The gut microbial community was highly diversity before infection and was dominated by Firmicutes, Fusobacteria, Bacteroidetes, and Proteobacteria. Antibiotic administration decreased the diversity of the gut microbiota and led to an outgrowth of Lactobacillus. The relative abundance of Proteobacteria, Gammaproteobacteria, Enterobacteriales, Lachnospiraceae, Enterobacteriaceae, Escherichia, Blautia, and Tyzzerella increased following C. difficile infection. These taxa could be biomarkers for C. difficile colonization. CONCLUSIONS: In general, the disease symptoms, histopathology, and gut microbiota changes following C. difficile infection in tree shrews were similar to those observed in humans.

Tree shrew bone marrow-derived mesenchymal stem cells express CD81, OCLN, and miR-122, facilitating the entire hepatitis C virus life cycle.

Hepatitis C virus (HCV) infection is a major cause of chronic liver disease and associated cirrhosis, and hepatocellular carcinoma worldwide. At present, there is no prophylactic vaccine against HCV due to the lack of in vivo and in vitro model systems. Although most recombinants of all major HCV genotypes replicate in Huh-7 cell line and derivatives, these cells are human hepatoma-derived cell line. Therefore, the development of un-tumor-derived cell systems facilitating the entire HCV life cycle is urgently needed. In this study, we aimed to establish a novel tree shrew-derived bone marrow-derived mesenchymal stem cell (BM-MSC) system to reconstruct the HCV life cycle. We transduction cluster of differentiation 81 (CD81), occludin (OCLN), and microRNA-122 (miR-122) into BM-MSCs, then used a well-established HCV, produced from the J6/JFH1-Huh7.5.1 culture system, to infect the cells. We observed that BM-MSCs transduction with CD81/OCLN or CD81/OCLN/miR-122 support HCV RNA replication and infectious virus production. We also found that the addition of exogenous vascular endothelial growth factor (VEGF) can enhance HCV infectivity in BM-MSCs, with HCV virus load up to 105 copies/mL. In conclusion, we identified the minimum essential factors required for HCV replication in tree shrew-derived nonhuman nonhepatic BM-MSCs. Further, we identified that exogenous addition of VEGF, and exogenous expression of CD81, OCLN, and miR-122, facilitates efficient viral replication and production of infectious particles. Our results describe a novel cell system capable of supporting the entire HCV life cycle, which may provide an essential tool for anti-HCV drug discovery, vaccine development, and study of pathogenesis.

Isolation and identification of two new strains of mammalian orthoreovirus from Chinese tree shrews.

Chinese tree shrews have been used extensively in studies of different types of cancer and for the modeling of viral infections. In the present study, we report the isolation and characterization of two strains of mammalian orthoreovirus (MRV), MRV1/TS/2011 and MRV3/TS/2012, which were isolated from the feces of tree shrews in Yunnan, China. These two strains of MRV were isolated and cultured in both primary tree shrew intestinal epithelial cells (pTIECs) and primary tree shrew alveolar epithelial cells (pTAECs). A neutralization test using immunofluorescence was employed to determine the subtype of each isolate. Viral RNA was extracted and analyzed by polyacrylamide gel electrophoresis (PAGE), and the sequence was determined by next-generation sequencing for construction of a phylogenetic tree and analysis of gene polymorphism. Electron microscopy examination revealed the presence of virus particles with the typical morphological characteristics of MRV. Serotype analysis showed that strain MRV1/TS/2011 was of type I and strain MRV3/TS/2012 was of type III. A sequence comparison showed that the isolates were 25.4% identical in the S1 gene.

Identification, characterization and expression profiles of PSEN2 in the Chinese tree shrew (Tupaia belangeri chinensis).

The gene PSEN2 encodes presenilin-2, a subunit of γ-secretase. Mutations in PSEN2 are not only related to Alzheimer's disease but are also involved in other diseases. The Chinese tree shrew (Tupaia belangeri chinensis) is a potential animal model for Alzheimer's disease, although little is known about its cDNA sequence, protein structure, and PSEN2 expression. To better understand PSEN2 in the tree shrew, we cloned this gene by rapid amplification of cDNA ends technology. Hence, we analyzed the sequence and molecular characteristics of PSEN2 mRNA, predicted its spatial structure, and analyzed its expression profiles. We found that tree shrew PSEN2 is 1539 base pairs in length and encodes 330 amino acids. It is homologous and genetically similar to humans (97.64% identity). The protein structure of tree shrew PSEN2 indicated similarities to human PSEN2, both being comprised of numerous transmembrane helices. However, tree shrew PSEN2 possesses seven α-helices, and thus lacks three compared with human PSEN2. Tree shrew PSEN2 mRNAs were ubiquitously detected in all tissues, with a tissue- and temporal-specific pattern. These results pave the way towards the function of tree shrew PSEN2, which will give insights into the mechanisms leading to neurodegenerative and other diseases in humans.

Gastrointestinal microbiota and metabolites possibly contribute to distinct pathogenicity of SARS-CoV-2 proto or its variants in rhesus monkeys.

Gastrointestinal (GI) infection is evidenced with involvement in COVID-19 pathogenesis caused by SARS-CoV-2. However, the correlation between GI microbiota and the distinct pathogenicity of SARS-CoV-2 Proto and its emerging variants remains unclear. In this study, we aimed to determine if GI microbiota impacted COVID-19 pathogenesis and if the effect varied between SARS-CoV-2 Proto and its variants. We performed an integrative analysis of histopathology, microbiomics, and transcriptomics on the GI tract fragments from rhesus monkeys infected with SARS-CoV-2 proto or its variants. Based on the degree of pathological damage and microbiota profile in the GI tract, five of SARS-CoV-2 strains were classified into two distinct clusters, namely, the clusters of Alpha, Beta and Delta (ABD), and Proto and Omicron (PO). Notably, the abundance of potentially pathogenic microorganisms increased in ABD but not in the PO-infected rhesus monkeys. Specifically, the high abundance of UCG-002, UCG-005, and Treponema in ABD virus-infected animals positively correlated with interleukin, integrins, and antiviral genes. Overall, this study revealed that infection-induced alteration of GI microbiota and metabolites could increase the systemic burdens of inflammation or pathological injury in infected animals, especially in those infected with ABD viruses. Distinct GI microbiota and metabolite profiles may be responsible for the differential pathological phenotypes of PO and ABD virus-infected animals. These findings improve our understanding the roles of the GI microbiota in SARS-CoV-2 infection and provide important information for the precise prevention, control, and treatment of COVID-19.

Motor Function in MPTP-Treated Tree Shrews (Tupaia belangeri chinensis).

The tree shrew, a new experimental animal model, has been used to study a variety of diseases, especially diseases of the nervous system. 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is the gold standard for toxin-based animal models of Parkinson's disease (PD) because MPTP treatment replicates almost all of the pathological hallmarks of PD. Therefore, in this study, the effects of MPTP on the motor function of the tree shrew were examined. After five daily injections of a 3 mg/kg dose of MPTP, the motor function of MPTP-injected tree shrews decreased significantly, and the classic Parkinsonian symptoms of action and resting tremor, bradykinesia, posture abnormalities, and gait instability were observed in most MPTP-injected tree shrews. HPLC results also showed significantly reduced striatal dopamine and 3,4-dihydroxyphenylacetic acid levels in tree shrews after MPTP injection. Increased oxidative stress levels are usually considered to be the cause of dopaminergic neuron depletion in the presence of MPTP and were observed in the substantia nigra of MPTP-treated tree shrews, as indicated by a significant reduction in superoxide dismutase and glutathione peroxidase activity and increased levels of malondialdehyde. In addition, elevated α-synuclein mRNA levels in the midbrain of MPTP-treated tree shrews were observed. Furthermore, MPTP-treated tree shrews showed the classic Parkinsonian symptoms at a lower MPTP dosage compared with other animal models. Thus, the MPTP-treated tree shrew may be a potential animal model for studying the pathogenesis of PD.

Single-cell transcriptomic atlas of distinct early immune responses induced by SARS-CoV-2 Proto or its variants in rhesus monkey.

Immune responses induced by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection play a critical role in the pathogenesis and outcome of coronavirus disease 2019 (COVID-19). However, the dynamic profile of immune responses postinfection by SARS-CoV-2 variants of concern (VOC) is not fully understood. In this study, peripheral blood mononuclear cells single-cell sequencing was performed to determine dynamic profiles of immune response to Prototype, Alpha, Beta, and Delta in a rhesus monkey model. Overall, all strains induced dramatic changes in both cellular subpopulations and gene expression levels at 1 day postinfection (dpi), which associated function including adaptive immune response, innate immunity, and IFN response. COVID-19-related genes revealed different gene profiles at 1 dpi among the four SARS-CoV-2 strains, including genes reported in COVID-19 patients with increased risk of autoimmune disease and rheumatic diseases. Delta-infected animal showed inhibition of translation pathway. B cells, T cells, and monocytes showed much commonality rather than specificity among the four strains. Monocytes were the major responders to SARS-CoV-2 infection, and the response lasted longer in Alpha than the other strains. Thus, this study reveals the early immune responses induced by SARS-CoV-2 Proto or its variants in nonhuman primates, which is important information for controlling rapidly evolving viruses.

Three doses of prototypic SARS-CoV-2 inactivated vaccine induce cross-protection against its variants of concern.

Variants are globally emerging very quickly following pandemic prototypic SARS-CoV-2. To evaluate the cross-protection of prototypic SARS-CoV-2 vaccine against its variants, we vaccinated rhesus monkeys with three doses of prototypic SARS-CoV-2 inactivated vaccine, followed by challenging with emerging SARS-CoV-2 variants of concern (VOCs). These vaccinated animals produced neutralizing antibodies against Alpha, Beta, Delta, and Omicron variants, although there were certain declinations of geometric mean titer (GMT) as compared with prototypic SARS-CoV-2. Of note, in vivo this prototypic vaccine not only reduced the viral loads in nasal, throat and anal swabs, pulmonary tissues, but also improved the pathological changes in the lung infected by variants of Alpha, Beta, and Delta. In summary, the prototypic SARS-CoV-2 inactivated vaccine in this study protected against VOCs to certain extension, which is of great significance for prevention and control of COVID-19.

Histones released by NETosis enhance the infectivity of SARS-CoV-2 by bridging the spike protein subunit 2 and sialic acid on host cells.

Neutrophil extracellular traps (NETs) can capture and kill viruses, such as influenza viruses, human immunodeficiency virus (HIV), and respiratory syncytial virus (RSV), thus contributing to host defense. Contrary to our expectation, we show here that the histones released by NETosis enhance the infectivity of SARS-CoV-2, as found by using live SARS-CoV-2 and two pseudovirus systems as well as a mouse model. The histone H3 or H4 selectively binds to subunit 2 of the spike (S) protein, as shown by a biochemical binding assay, surface plasmon resonance and binding energy calculation as well as the construction of a mutant S protein by replacing four acidic amino acids. Sialic acid on the host cell surface is the key molecule to which histones bridge subunit 2 of the S protein. Moreover, histones enhance cell-cell fusion. Finally, treatment with an inhibitor of NETosis, histone H3 or H4, or sialic acid notably affected the levels of sgRNA copies and the number of apoptotic cells in a mouse model. These findings suggest that SARS-CoV-2 could hijack histones from neutrophil NETosis to promote its host cell attachment and entry process and may be important in exploring pathogenesis and possible strategies to develop new effective therapies for COVID-19.

Genome-wide DNA methylome and whole-transcriptome landscapes of spontaneous intraductal papilloma in tree shrews.

BACKGROUND: Breast intraductal papilloma (IP) is mainly caused by the abnormal proliferation of ductal epithelial cells. Tree shrews have potential as an animal model for the study of breast tumours; however, little is known regarding the transcriptome and DNA methylome landscapes of breast IP in tree shrews. In this research, we conducted whole-genome DNA methylation and transcriptome analyses of breast IP and normal mammary glands in tree shrews. METHODS: DNA methylation profiles were generated from the whole-genome bisulfite sequencing and whole-transcriptome landscapes of IP and control groups of tree shrews through strand-specific library construction and RNA sequencing. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes functional enrichment analyses and gene set enrichment analysis were performed. Spearman's correlation analysis was used to identify statistical relationships between gene expression and DNA methylation. RESULTS: A genome-wide perspective of the epigenetic regulation of protein-coding genes in breast IP in tree shrews was obtained. The methylation levels at CG sites were considerably higher than those at CHG or CHH sites, and were highest in gene body regions. In total, 3,486, 82 and 361 differentially methylated regions (DMRs) were identified in the context of CG, CHG, and CHH, respectively, and 701 differentially methylated genes (DMGs) were found. Further, through transcriptomic analysis, 62 differentially expressed genes, 50 long noncoding RNAs, and 32 circular RNAs were identified in breast IP compared to normal mammary glands. Correlation analysis between the DNA methylation and transcriptome data revealed that 25 DMGs were also differentially expressed genes, among which the expression levels of 9 genes were negatively correlated with methylation levels in gene body regions. Importantly, integrated analysis identified 3 genes (PDZ domain-containing 1, ATPase plasma membrane Ca2+ transporting 4 and Lymphocyte cytosolic protein 1) that could serve as candidates for further study of breast IP in tree shrews. CONCLUSIONS: This research has unearthed the comprehensive landscape of the transcriptome and DNA methylome of spontaneous IP in tree shrews, as well as candidate tumorigenesis related genes in IP. These results will contribute to the use of tree shrews in animal models of breast tumours.

First report of Schistosoma sinensium infecting Tupaia belangeri and Tricula sp. LF.

Schistosoma sinensium belongs to the Asian Schistosoma and is transmitted by freshwater snails of the genus Tricula. Rodents are known definitive hosts of S. sinensium. In 2016, suspected schistosome eggs were found in the feces of the northern tree shrew (Tupaia belangeri) in a field in Lufeng County (latitude, 25°04'50″ N; longitude, 102°19'30″ E; altitude 1820 m), Yunnan Province, China. Morphological analysis suggested that the schistosome was S. sinensium. 18S, 12S and CO1 genes sequencing and phylogenetic analysis showed that this species had the highest similarity to and occupied the same evolutionary branch as S. sinensium from Mianzhu, Sichuan, China. Meanwhile, based on 16S and 28S rDNA sequencing and morphological identification, the snail intermediate host was identified as a species of Tricula, and was found in irrigation channels. Phylogeny indicated that Tricula sp. LF was a sister taxon to T. bambooensis, T. ludongbini. The S. sinensium was able to experimentally infect the captive-bred Tupaia belangeri, and Schistosoma eggs were recovered from all Tupaia belangeri exposed. In this study, we report the infection of Tupaia belangeri and Tricula sp. LF with S. sinensium in Lufeng, Yunnan, southwest China. These findings may improve our understanding of the host range, evolution, distribution, and phylogenetic position of S. sinensium.

The olfactory route is a potential way for SARS-CoV-2 to invade the central nervous system of rhesus monkeys.

Neurological manifestations are frequently reported in the COVID-19 patients. Neuromechanism of SARS-CoV-2 remains to be elucidated. In this study, we explored the mechanisms of SARS-CoV-2 neurotropism via our established non-human primate model of COVID-19. In rhesus monkey, SARS-CoV-2 invades the CNS primarily via the olfactory bulb. Thereafter, viruses rapidly spread to functional areas of the central nervous system, such as hippocampus, thalamus, and medulla oblongata. The infection of SARS-CoV-2 induces the inflammation possibly by targeting neurons, microglia, and astrocytes in the CNS. Consistently, SARS-CoV-2 infects neuro-derived SK-N-SH, glial-derived U251, and brain microvascular endothelial cells in vitro. To our knowledge, this is the first experimental evidence of SARS-CoV-2 neuroinvasion in the NHP model, which provides important insights into the CNS-related pathogenesis of SARS-CoV-2.

WGCNA analysis of the subcutaneous fat transcriptome in a novel tree shrew model.

IMPACT STATEMENT: We constructed the transcriptomic network in adipose tissue in lean, moderate obesity and severe obesity groups of tree shrew for the first time. Compared to other laboratory animal models, the tree shrew is a prospective laboratory animal that has a closer genetic association with primates than with rodents. It is widely used in biomedical researches. Enrichment analyses revealed several molecular biological processes were involved in the ribosome, lysosome, and ubiquitin-mediated proteolysis process. These results provided insights into new targets for the prevention and therapy of obesity and a novel research model for obesity.

mRNA profiling reveals response regulators of decreased fungal keratitis symptoms in a tree shrew model.

Fungal keratitis is a corneal disease with a high blindness rate caused by pathogenic fungal infections. The pathogenesis of fungal keratitis and the immune response after fungal infection are still unclear. Notably, the pathological features of fungal keratitis in tree shrews are similar to those in humans. In the present study, mRNA profiling of tree shrew corneas with fungal keratitis was performed. GO and KEGG enrichment analyses were performed on the differentially expressed mRNAs, and the GO biological process ontology was used to analyze functional trends in the differentially expressed mRNAs. In total, 151 downregulated and 71 upregulated mRNAs were shared among the 7-day, 14-day and 30-day infection groups. These differentially expressed mRNAs were significantly enriched in the GO category immune response (GO: 0002376) and the KEGG pathways cytokine receptor binding (KEGG ID: tup04060) and cell adhesion (KEGG ID: tup04514). The downregulated mRNAs were significantly enriched in the corneal epithelial cell adhesion function. Fifty-eight initially upregulated mRNAs gradually decreased in expression, and these mRNAs were significantly enriched in the functions lipopolysaccharide (LPS) and antibacterial polypeptide recognition, cell differentiation, and cell rearrangement. Zeta chain of T-cell receptor associated protein kinase 70 (ZAP70), lymphocyte cytosolic protein 2 (LCP2), C-C motif chemokine and its receptor showed high degrees of connectivity in the protein-protein interaction (PPI) network. We speculate that the decrease in symptoms of tree shrew fungal keratitis may be related to the upregulation of genes involved in immune regulation and macrophage colony stimulation. This study showed that the C-C motif chemokine and its receptor may play a key role in regulating tree shrew fungal keratitis, providing a theoretical basis for studying the pathogenesis of human fungal keratitis.

Comparative genomic analysis of Proteus spp. isolated from tree shrews indicated unexpectedly high genetic diversity.

Proteus spp. are commensal gastrointestinal bacteria in many hosts, but information regarding the mutual relationships between these bacteria and their hosts is limited. The tree shrew is an alternative laboratory animal widely used for human disease research. However, little is known about the relationship between Proteus spp. and tree shrews. In this study, the complete genome sequencing method was used to analyse the characteristics of Proteus spp. isolated from tree shrews, and comparative genomic analysis was performed to reveal their relationships. The results showed that 36 Proteus spp. bacteria were isolated, including 34 Proteus mirabilis strains and two Proteus vulgaris strains. The effective rate of sequencing was 93.53%±2.73%, with an average GC content of 39.94%±0.25%. Briefly, 3682.89±90.37, 2771.36±36.01 and 2832.06±42.49 genes were annotated in the NCBI non-redundant nucleotide database (NR), SwissProt database and KEGG database, respectively. The high proportions of macrolide-, vancomycin-, bacitracin-, and tetracycline-resistance profiles of the strains were annotated in the Antibiotic Resistance Genes Database (ARDB). Flagella, lipooligosaccharides, type 1 fimbriae and P fimbriae were the most abundantly annotated virulence factors in the Virulence Factor Database (VFDB). SNP variants indicated high proportions of base transitions (Ts), homozygous mutations (Hom) and non-synonymous mutations (Non-Syn) in Proteus spp. (P<0.05). Phylogenetic analysis of Proteus spp. and other references revealed high genetic diversity for strains isolated from tree shrews, and host specificity of Proteus spp. bacteria was not found. Overall, this study provided important information on characteristics of genome for Proteus spp. isolated from tree shrews.

A tree shrew model for steroid-associated osteonecrosis.

Osteonecrosis is a common human disease in orthopedics. It is difficult to treat, and half of patients may need artificial joint replacement, resulting in a considerable economic burden and a reduction in quality of life. Hormones are one of the major causes of osteonecrosis and high doses of corticosteroids are considered the most dangerous factor. Because of the complexity of treatment, we still need a better animal model that can be widely used in drug development and testing. Tree shrews are more closely related to primates than rodents. As such, we constructed a successful tree shrew model to establish and evaluate steroid-associated osteonecrosis (SAON). We found that low-dose lipopolysaccharide (LPS) combined with high-dose methylprednisolone (MPS) over 12 weeks could be used to establish a tree shrew model with femoral head necrosis. Serum biochemical and histological analyses showed that an ideal model was obtained. Thus, this work provides a useful animal model for the study of SAON and for the optimization of treatment methods.

Susceptibility of tree shrew to SARS-CoV-2 infection.

Since severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) became a pandemic event in the world, it has not only caused huge economic losses, but also a serious threat to global public health. Many scientific questions about SARS-CoV-2 and Coronavirus disease (COVID-19) were raised and urgently need to be answered, including the susceptibility of animals to SARS-CoV-2 infection. Here we tested whether tree shrew, an emerging experimental animal domesticated from wild animal, is susceptible to SARS-CoV-2 infection. No clinical signs were observed in SARS-CoV-2 inoculated tree shrews during this experiment except the increasing body temperature particularly in female animals. Low levels of virus shedding and replication in tissues occurred in all three age groups. Notably, young tree shrews (6 months to 12 months) showed virus shedding at the earlier stage of infection than adult (2 years to 4 years) and old (5 years to 7 years) animals that had longer duration of virus shedding comparatively. Histopathological examine revealed that pulmonary abnormalities were the main changes but mild although slight lesions were also observed in other tissues. In summary, tree shrew is less susceptible to SARS-CoV-2 infection compared with the reported animal models and may not be a suitable animal for COVID-19 related researches. However, tree shrew may be a potential intermediate host of SARS-CoV-2 as an asymptomatic carrier.

Comparison of nonhuman primates identified the suitable model for COVID-19.

Identification of a suitable nonhuman primate (NHP) model of COVID-19 remains challenging. Here, we characterized severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in three NHP species: Old World monkeys Macaca mulatta (M. mulatta) and Macaca fascicularis (M. fascicularis) and New World monkey Callithrix jacchus (C. jacchus). Infected M. mulatta and M. fascicularis showed abnormal chest radiographs, an increased body temperature and a decreased body weight. Viral genomes were detected in swab and blood samples from all animals. Viral load was detected in the pulmonary tissues of M. mulatta and M. fascicularis but not C. jacchus. Furthermore, among the three animal species, M. mulatta showed the strongest response to SARS-CoV-2, including increased inflammatory cytokine expression and pathological changes in the pulmonary tissues. Collectively, these data revealed the different susceptibilities of Old World and New World monkeys to SARS-CoV-2 and identified M. mulatta as the most suitable for modeling COVID-19.