Susceptibility of tree shrew to SARS-CoV-2 infection

Since 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 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 (above 39{degrees} C) particular in female animals during infection. Low levels of virus shedding and replication in tissues occurred in all three age groups, each of which showed his own characteristics. Histopathological examine revealed that pulmonary abnormalities were mild but the main changes although slight lesions were also observed in other tissues. In summary, tree shrew is not susceptible to SARS-CoV-2 infection and may not be a suitable animal for COVID-19 related researches.

Comparison of SARS-CoV-2 infections among 3 species of non-human primates

COVID-19, caused by SARS-CoV-2 infection, has recently been announced as a pandemic all over the world. Plenty of diagnostic, preventive and therapeutic knowledges have been enriched from clinical studies since December 2019. However, animal models, particularly non-human primate models, are urgently needed for critical questions that could not be answered in clinical patients, evaluations of anti-viral drugs and vaccines. In this study, two families of non-human primates, Old world monkeys (12 Macaca mulatta, 6 Macaca fascicularis) and New world monkeys (6 Callithrix jacchus), were experimentally inoculated with SARS-CoV-2. Clinical signs were recorded. Samples were collected for analysis of viral shedding, viremia and histopathological examination. Increased body temperature was observed in 100% (12/12) M. mulatta, 33.3% (2/6) M. fascicularis and none (0/6) of C. jacchus post inoculation of SARS-CoV-2. All of M. mulatta and M. fascicularis showed chest radiographic abnormality. Viral genomes were detected in nasal swabs, throat swabs, anal swabs and blood from all 3 species of monkeys. Viral shedding from upper respiratory samples reached the peak between day 6 and day 8 post inoculation. From necropsied M. mulatta and M. fascicularis, the tissues showing virus positive were mainly lung, weasand, bronchus and spleen. No viral genome was seen in any of tissues from 2 necropsied C. jacchus. Severe gross lesions and histopathological changes were observed in lung, heart and stomach of SARS-CoV-2 infected animals. In summary, we have established a NHP model for COVID-19, which could be used to evaluate drugs and vaccines, and investigate viral pathogenesis. M. mulatta is the most susceptible to SARS-CoV-2 infection, followed by M. fascicularis and C. jacchus. One Sentence SummaryM. mulatta is the most susceptible to SARS-CoV-2 infection as compared to M. fascicularis and C. jacchus.

Characteristics and changes of the CD molecules and IFN-γ expressions in tree shrews infected with mammalian orthoreovirus / 中国实验动物学报

Objective To explore the characteristics of immunological changes in tree shrews infected with orthoreovirus, and provide a theoretical basis for the prevention of virus in tree shrews. Methods 40 -50-day-old tree shrews were divided into three groups: MRV1/TS/2011 virus-infected and MRV3/TS/2013 virus-infected groups, and saline-treated control group. On the 1, 8, 14, 21, and 28 days after infection, blood samples were taken from the tail vein and used for RT-PCR, flow cytometry and ELISA detection, to assess the viral load, number of CD4/CD8/CD19 cells, and IFN-gamma expression. Results The MRV1/TS/2011 and MRV3/TS/2013 viral load in the plasma and the number of CD4 +and CD19 +cells reached a peak at the 14th day after infection. At the first day after MRV1/TS/2011 infection, the CD4 +cells had a significantly higher expression compared with the normal group. CD8 +cells and the IFN-gamma expression reached a peak at the 21st day after infection. The expression of CD4 +was even higher after MRV1/TS/2011 infection, and the expression of CD8 +cells was higher after MRV3/TS/2013 infection. Conclusions We would conclude that after MRV1/TS/2011 and MRV3/TS/2011 virus infection, accompanying the changes of viral load, it shows some regularity of the expression of CD4/CD8/CD19 and IFN-gamma in the tree shrews: at the early stage of MRV1/TS/2011 virus infection, humoral immunity is stimulated, and CD4 +cells play a major role. MRV3/TS/2013 virus may mainly affect the cellular immunity, while humoral immunity only plays a role at a high viral expression or the late stage of infection. CD4 +cells may be more sensitive to type 1 reovirus, and CD19 +cells may be more sensitive to type 3 reovirus.

Establishment of an osteoporosis model in tree shrews by bilateral ovariectomy / 中国实验动物学报

Objective To establish an osteoporosis model in tree shrews by bilateral ovariectomy.Methods One hundred healthy 6-24 month old female tree shrews were used in this study.The diagnosis and treatment of osteoporo-sis in the model tree shrews was assessed according to the Interpretation of the Clinical Practice Guideines for Primary Oste-oporosis 2011 released by the Chinese Medical Association of Osteoporosis and Bone Mineral Salt Disease Branch.① Ac-cording to the human natural life span, sexual maturation time and peak bone mineral density ( PBMD) and the tree shrew natural life span and sexual maturation time, we estimated the PBMD of tree shrew in the age of months.Six 6-, 12-, 18-and 24-month old tree shrews in each group were randomly taken for measurement of BMD, and compared the differences between groups to verify the PBMD age of tree shrews.②We chose 62 6-month old tree shrews from the rest of tree shrews to measure their BMD to determine the mean and standard deviation of BMD.Then we divided them into study group ( n =32) and control group (n =30).Bilateral ovariectomy was performed in the study group, while omentectomy was done in the control group.BMD was measured at 3, 6, 9, 12 months after the surgery, 6 animals from each group.The animals which met the criteria of guideline were taken for pathological examination.Results ①The PBMD of 6-, 12-, 18-, 24-month old tree shrews was 0.138 ±0.012, 0.143 ±0.010, 0.141 ±0.009, and 0.139 ±0.009) g/cm2 , respectively, showing no significant differences among them (P>0.05).②The mean PBMD of the tree shrews was 0.143 ±0.016 g/cm2 .③In the model groups, the number of tree shrews whose BMD met the criteria of guideline was 0, 5, 4, 5, respec-tively.The pathological examination of the proximal tibia from the model group showed sparse and some disrupted trabecu-lae and enlarged inter-trabecular space.In the control group, the tibia tissues showed normal histology of bone structure and no one tree shrew showed a BMD value which met the criteria of diagnosis of osteoporosis.Conclusions An osteopo-rosis model in tree shrews can be established at 6 months after bilateral ovariectomy, showing similar manifestation of osteo-porosis in postmenopausal women.The success rate of this modeling method is high and the model is stable.

Progress in application of tree shrew models in research on human viral diseases / 中国实验动物学报

Tree shrews get more and more concerns due to many of its physiological , biochemical and anatomical characteristics similar to those of human beings .Therefore, tree shrews models of human diseases such as viral diseases , neurological diseases and tumors attract more and more attention of researchers .In this article we will review the recent ad-vances in application of tree shrew models in research on human viral diseases .

Histological observation of the major endocrine organs in laboratory tree shrews / 中国比较医学杂志

Objective To understand the histological characteristics of the major endocrine organs of tree shrew , and provide a normal histological atlas of endocrine organs of tree shrew .Methods Ten artificially fed healthy tree shrews were killed and dissected after anesthesia .The thyroid, parathyroid, adrenal and pituitary glands were observed by gross inspection and samples were taken for routine histological examination with HE staining .Results ( 1 ) The thyroid gland was pale yellow, located on both sides of the 2-4 tracheal rings.The thyroid gland was plate-shaped, its surface was covered with a thin fibrous capsule . The thyroid parenchyma was divided into several lobules by stretched capsule membrane .Follicular and parafollicular cells were distributed in the lobules , and red colloid was present in follicular cavity.(2) Each side had one parathyroid , located on the cranial or the outer surface of the middle part of the thyroid gland, and was slightly covered by thyroid .The gland was round or oval , and its parenchyma was made up of the principal cells and eosinophil cells , and acinar structure appeared in the parenchyma .( 3 ) The adrenal glands were oval , yellow color, located in the renal hili , and linked to the kidneys .They were surrounded by a thin capsule .The parenchyma was divided into cortex and medulla .The cortex was divided into zona glomerulosa , zona fasciculata and zona reticularis from outside to inside.The zona glomerulosa was the thickest layer and the zona fasciculata was the thinnest .The medulla cells formed clumps or mesh, with central vein in the central part .(4) The pituitary gland was located in the sella turcica , with no recessus hypophysis .The pituitary gland was composed of the adenohypophysis and neurohypophysis .Its surface was covered with a connective tissue capsule .The pituitary gland was divided into distal part , middle part and pars tuberalis . neurohypophysis was made up of neural and pars infundibularis .Conclusions The histological atlas of endocrine organs in the tree shrew is established , which is close to that of the primate animals in the morphology , and provide histological evidence for the study of tree shrew endocrine organs and disorders , as well as the animal model of human diseases .

Isolation,culture, adipocgenic and osteogenic induction of Tupaia bone marrow mesenchymal stem cells / 中国比较医学杂志

Objective To study the isolation,culture, adipogenic and osteogenic induction Tupaia bone marrow mesenchymal stem cells(BM-MSCs).Method The BM-MSCs from tupaia were isolated and expended by combination of gradient centrifugation and adherence culture , then subcultured and observed for morphology under inverted phase contrast microscope.BM-MSCs were induced to adipocytes .and osteoblasts in vitro Result Cells were spindle or triangle-shaped, and clone proliferation .Cells were successfully induced into adipocytes .and osteoblasts Conclusions The method of isolation BM-MSCs from tupaia by combination of gradient centrifugation and adherence culture is simple and feasible , BM-MSCs have differentiation potential into adipocytes and osteoblasts .

Infection investigation of Toxoplasma gondii in tree shrews from various sources / 中国比较医学杂志

Objective To investigate the infection status of Toxoplasma gondii in different colonies of tree shrews and then provide the basis for parasitological monitoring .Methods Each of the forty blood samples were randomly collected from three tree shrews colonies : wild origin, domesticated and first generation, respectively.Both indirect hemagglutination test (IHA) and PCR assay were used to detect the Toxoplasma gondii.Results No positive sample of Toxoplasma gondii was detected from either IHA or PCR results .The results from IHA and PCR assays were in coincidence with each other.Conclusions According to the survey none of the tree shrews from the three groups is infected with Toxoplasma gondii.More samples or infection experiments are needed to determine whether tree shrews can be infected with Toxoplasma gondii.