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Age is a risk factor for coronavirus disease 2019 (COVID-19) associated morbidity and mortality in humans; hence, in this study, we compared the course of severe acute respiratory syndrome–coronavirus 2 (SARS-CoV-2) infection in young and aged BALB/c mice. We found that SARS-CoV-2 isolates replicated in the respiratory tracts of 12-month-old (aged) mice and caused pathological features of pneumonia upon intranasal infection. In contrast, rapid viral clearance was observed 5 days following infection in 2-month-old (young) mice with no evidence of pathological changes in the lungs. Infection with SARS-CoV-2 elicited significantly upregulated production of cytokines, especially interleukin 6 and interferon gamma, in aged mice; whereas this response was much weaker in young mice. Subsequent challenge of infected aged BALB/c mice with SARS-CoV-2 resulted in neutralized antibody responses, a significantly reduced viral burden in the lungs, and inflammation mitigation. Deep sequencing showed a panel of mutations potentially associated with the enhanced infection in aged BALB/c mice, such as the Q498H mutations which are located at the receptor binding domain (RBD) of the spike (S) protein. We further found that the isolates can not only multiply in the respiratory tract of mice but also cause disease in aged mice. Overall, viral replication and rapid adaption in aged BALB/c mice were associated with pneumonia, confirming that the age-related susceptibility to SARS-CoV-2 in mice resembled that in humans. Importance Aged BALB/c model are in use as a model of disease caused by SARS-CoV-2. Our research demonstrated SARS-CoV-2 can rapidly adapt in aged BALB/c mice through causing mutations at the RBD of the S protein. Moreover, SARS-CoV-2-infected aged BALB/c mice indicated that alveolar damage, interstitial pneumonia, and inflammatory immune responses were similar to the clinical manifestations of human infections. Therefore, our aged BALB/c challenge model will be useful for further understanding the pathogenesis of SARS-CoV-2 and for testing vaccines and antiviral agents.

Summary The novel coronavirus disease (COVID‐19) caused by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) has resulted in an unprecedented public health crisis and economic losses. Although several cases of cats and dogs infected with SARS‐CoV‐2 have been reported during this outbreak, the prevalence of SARS‐CoV‐2 in dog and its transmission among other companion animals are still unknown. Here, we report an extensive serological study of SARS‐CoV‐2 infection in dogs in Wuhan and analyze the infection rates at different stages of the pandemic outbreak. A total of 946 dogs serum samples were collected from Wuhan, of which 36 samples were obtained prior to the pandemic outbreak. Indirect enzyme linked immunosorbent assay (ELISA) showed that 16 sera collected during the outbreak were detected as positive through the receptor binding domain (RBD) of SARS‐CoV‐2. Of these 16 sera, 10 exhibited measurable SARS‐CoV‐2 specific neutralizing antibodies whose titers ranged from 1/20 to 1/180. No serological cross‐reactivity was detected between SARS‐CoV‐2 and canine coronavirus (CCV). Furthermore, with the effective control of the outbreak, a decrease in the SARS‐CoV‐2 seropositive dog number was observed. Our results suggest that SARS‐CoV‐2 has infected companion dogs during the outbreak, and that COVID‐19 patient families have a higher risk of dog infection. Our findings deepen our understanding of the infection of SARS‐CoV‐2 in dogs and provide an important reference for prevention of COVID‐19.

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To investigate the roles and explore the altered expression of microRNAs (miRNAs) and mRNAs in chicken embryos in response to Newcastle disease virus (NDV) infection, deep sequencing was performed. Then, a conjoint analysis of small RNA-seq and mRNA-seq was performed to screen interactional miRNA–mRNA pairs during NDV infection. In total, 15 and 17 up- and downregulated miRNAs were identified that potentially targeted 4279 and 6080 mRNAs in NDV-infected chicken embryonic tissues, respectively; in addition, 595 upregulated and 480 downregulated mRNAs were identified. The conjoint analysis of the obtained data identified 1069 miRNA–mRNA pairs. Among these pairs, 130 pairs were related to immune or inflammatory responses. The relationship between gga-miR-203a and its target transglutaminase 2 (TGM2) was confirmed using a dual-luciferase reporter system and a real time quantitative polymerase chain reaction (RT-qPCR) assay. Overall, the discovery of miRNAs, mRNAs, and their potential pairing relationships, which may be involved in the regulation of NDV infection, will facilitate our understanding of the complex regulatory relationship between the host and the virus.

Erysipelothrix rhusiopathiae can cause erysipelas in animals and erysipeloid in humans. Since its recurrence in 2012, swine erysipelas has caused serious losses within the pig industry in China. The aim of this study was to perform multilocus sequence typing and understand the virulence and antimicrobial susceptibility of E. rhusiopathiae isolates in China. Multilocus sequence typing (MLST) of a total of 120 strains was performed, and as a result, three different sequence types were identified, of which ST48 was the main one. Five isolates of each MLST type were randomly selected to be used to challenge mice. ST48 was associated with a higher virulence. Antimicrobial susceptibility was tested using a microdilution technique and, to analyze the resistance mechanism, six strains were selected for genome sequencing. A comparison of the six genomes indicated the presence of a suspected macrolide resistance gene, namely, Erm(A)-like, in erythromycin-resistant strains, which increased the minimum inhibitory concentration (MIC) of erythromycin against E. coli C600 at least four-fold. In addition, three mutations (gyrA86T-I, gyrA90D-N, and parC81S-I) were observed in the quinolone resistance-determining regions (QRDRs) of gyrA and parC in quinolone-resistant strains. After the gyrA gene with the 86T-I mutation or the parC gene with the 81S-I mutation was transfected into E. coli C600, the MIC of enrofloxacin against this strain increased at least two-fold. Our findings provide a theoretical basis for developing antibacterial drugs and may contribute to the clinical prevention and control of E. rhusiopathiae.

African swine fever virus (ASFV) is an important viral pathogen infecting pigs worldwide throughout the pig industry. CD2v (an outer-membrane glycosylated protein of ASFV)-unexpressed lower-virulence mutants have appeared in China and other countries in recent years. Using OIE-recommended quantitative PCR and ELISA methods, people can accurately judge whether pigs are infected with wild-type ASFV. However, the strategy has failed to distinguish ΔCD2v lower-virulence mutants and wild-type ASFV infection. Here, we expressed and purified the CD2v and p30 proteins via CHO cells and successfully established a dual enzyme-linked immunosorbent assay (ELISA), which can be used to differentiate pigs infected with wild-type ASFV or with CD2v-unexpressed lower-virulence mutants. The dual ELISA showed excellent specificity without cross-reactions with antibodies of PRRSV, CSFV, JEV, PRV, or PPV. The dual ELISA could detect ASFV-infected positive serum samples up to dilutions of 5120 times, possessing high sensitivity. Therefore, the application of this dual ELISA approach can play an important role in ASFV epidemiology study and fill the gaps in differential diagnosis.

MicroRNAs regulate post-transcriptional gene expression via either translational repression or mRNA degradation. They have important roles in both viral infection and host anti-infection processes. We discovered that the miR-375 is significantly upregulated in Newcastle disease virus (NDV)-infected chicken embryonic visceral tissues using a small RNA sequencing approach. Further research revealed that the overexpression of miR-375 markedly decreases the replication of the velogenic NDV F48E9 and the lentogenic NDV La Sota by targeting the M gene of NDV in DF-1 cells. Interestingly, miR-375 has another target, ELAVL4, which regulates chicken fibrocyte cell cycle progression and decreases NDV proliferation. In addition, miR-375 can influence bystander cells by its secretion in culture medium. Our results indicated that miR-375 is an inhibitor of NDV, but can also enhance NDV growth by reducing the expression of its target ELAVL4. These results emphasize the complex roles of microRNAs in the regulation of viral infections.