First Specific Detection of Mammalian Orthoreovirus from Goats Using TaqMan Real-Time RT-PCR Technology

Genomic Characteristics and Pathogenicity of Novel Reassortant Mammalian Orthoreoviruses From Sheep, China

Mammalian orthoreoviruses (MRVs) have a wide geographic distribution worldwide and have been detected from humans and a variety of animal species. This study represents the first isolation of MRV from sheep rectal swabs in China, with analyses of its molecular and pathogenicity characteristics. MRV-positive samples were inoculated into Madin-Darby bovine kidney (MDBK) cells, resulting in stable cytopathic effects (CPEs) after three generations of blind passage. Two isolates were isolated and confirmed as MRV, named MRV-XJ23 and MRV-sheep/SY13, through reverse-transcription polymerase chain reaction (RT-PCR), transmission electron microscopy, and indirect immunofluorescence assay (IFA). The viruses exhibited broad cellular tropism. Whole-genome sequences were obtained and subjected to homology and evolutionary analyses, revealing that MRV-XJ23 and MRV-sheep/SY13 belong to the MRV-1 serotype. Phylogenetic analyses demonstrated that MRV-XJ23 is a reassortant virus containing gene segments from three MRVs that infected humans, bovines, and bats, with nucleotide homology exceeding 94.56%. The gene segments of MRV-sheep/SY13 were derived from five strains-Osaka2005, BatMRV-2/SNU1/Korea/2021, T1/human/Netherlands/1/84, IND/MZ/3013814/reo, and B/03-with nucleotide homology exceeding 95.47%. Animal experiments demonstrated that MRV-sheep/SY13 infection induced significant pathological changes in the respiratory and digestive tracts of mice. In sheep, MRV-sheep/SY13 caused respiratory infections, but no obvious lesion was observed from the digestive tract. This study expands our understanding of the MRV host range, reveals the potential public health risk of MRV transmission across species and zoonotic transmission, and underscores the necessity of further studies on epidemiology, reassortment patterns, and pathogenicity of MRV in sheep and domestic animals.

Sensitive and Accurate Quantification of Enterovirus-D68 (EV-D68) Viral Loads Using Droplet Digital PCR (ddPCR)

Enterovirus-D68 (EV-D68) is a reemerging virus that has been associated with numerous outbreaks in children in the past 10 years. Most assays examining viral infection kinetics have relied on the use of quantitative RT-PCR (qRT-PCR) assays as an assay of choice. Though valuable, there are inherent limitations that introduce variability, thereby reducing its value when comparing results across the field. Unlike the qRT-PCR assay that uses a standard curve to determine the copy number of viral RNA, the droplet digital PCR assay (ddPCR) directly quantifies the absolute number of copies within a given sample, which in turn makes the assay highly sensitive and accurate. Here, we have developed an EV-D68-specific ddPCR assay that effectively quantifies EV-D68 RNA copies in both cells and supernatants within a dynamic range of 6.7 × 10-3 copies/μL to 1.2 × 104 copies/μL of the sample. The assay was highly specific for a broad range of EV-D68 isolates (Fermon, US/MO/14-18947, US/MO/14-18949, US/KY/14-18953, USA/2018-23088, USA/2020-23336 and EV-D68-infected human nasal turbinate samples from the 2022 outbreak) without cross-reactivity to other viruses such as Enterovirus-A71 (EV-A71), Human Parechovirus (HPeV)-1 and -2, Coxsackievirus (CV)-B1, Human Coronavirus (HCoV)-NL63, SARS-CoV-2, Influenza-A and B, Rhinovirus, and Respiratory Syncytial Virus (RSV)-A2, which are known to cause infection in children. The assay was able to readily quantify EV-D68 in infected cells and supernatants along with nasal turbinate samples collected from children during the 2022 outbreak. Our results suggest that the assay can be readily translated to accurately quantify viral loads in tissues and body fluids such as plasma and lung or nasal aspirates.

Isolation and identification of a novel porcine-related recombinant mammalian orthoreovirus type 3 strain from cattle in Guangxi Province, China

The Mammalian orthoreovirus (MRV) infects various mammals, including humans, and is linked to gastrointestinal, respiratory, and neurological diseases. A recent outbreak in Liuzhou, Guangxi, China, led to the isolation of a new MRV strain, GXLZ2301, from fecal samples. This strain replicates in multiple cell lines and forms lattice-like structures. Infected cells exhibit single-cell death and syncytia formation. The virus's titers peaked at 107.2 TCID50/0.1 mL in PK-15 and BHK cells, with the lowest at 103.88 TCID50/0.1 mL in A549 cells. Electron microscopy showed no envelope with a diameter of about 70 nm. Genetic analysis revealed GXLZ2301 as a recombinant strain with gene segments from humans, cows, and pigs, similar to type 3 MRV strains from Italy (2015-2016). Pathogenicity tests indicated that while the bovine MRV strain did not cause clinical symptoms in mice, it caused significant damage to the gut, lungs, liver, kidneys, and brain. The emergence of this MRV strain may pose a threat to the health of animals and humans, and it is recommended that its epidemiology and recombination be closely monitored.