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Reoviruses (respiratory enteric orphan viruses) are non-enveloped, double-stranded RNA viruses that have served as a cornerstone for molecular virology research for over half a century. While initially termed "orphan" viruses because they were not associated with any specific disease, reoviruses are now recognized as significant pathogens in young animals and humans, as well as invaluable experimental models for studying viral replication, pathogenesis, and host immune responses. In recent years, reoviruses have gained substantial attention for their oncolytic properties, with the mammalian orthoreovirus (specifically serotype 3 Dearing strain) being developed as a cancer therapeutic agent. Understanding the virology, molecular targets, and pathological pathways of reoviruses is essential for both basic research and translational applications.
Figure 1. Reovirus infection cycle in the insect vector. (Khorramnejad, Ayda, et al. 2021)
Reoviruses belong to the family Reoviridae, a large family of viruses with double-stranded RNA genomes that infect a wide range of hosts, including vertebrates, invertebrates, plants, and fungi. The genus Orthoreovirus contains the mammalian reoviruses, which are the most extensively studied members.
The reovirus virion is non-enveloped and icosahedral, approximately 85 nm in diameter, with a distinctive double-layered capsid structure that confers exceptional stability in the environment. The genome consists of 10 segments of double-stranded RNA, classified into three size classes: large (L1–L3), medium (M1–M3), and small (S1–S4). Each segment encodes one or more proteins, with the S1 segment of mammalian reoviruses encoding two proteins through alternative translation initiation.
Three major serotypes of mammalian reoviruses are recognized:
Reoviruses are ubiquitous in nature, infecting humans and animals worldwide. In humans, infection typically occurs during childhood, with seropositivity reaching nearly 100% by adulthood. Transmission occurs via:
Most human infections are asymptomatic or result in mild, self-limited illness. However, in young children, the immunocompromised, and certain animal species, reoviruses can cause significant disease.
In humans, reovirus infection is generally mild, but several clinical presentations have been documented:
In animals, reoviruses cause more pronounced disease, including enteritis, respiratory disease, and arthritis in mice and other species, making them valuable models for studying viral pathogenesis.
Reovirus pathogenesis is a complex interplay between viral tropism, host immune responses, and tissue-specific factors. Following ingestion or inhalation, the virus replicates in the gastrointestinal or respiratory tract before disseminating to lymphoid tissues and target organs. Viral spread occurs via hematogenous and neural routes, with serotype-specific tropism determined largely by the viral attachment protein σ1.
Key features of reovirus pathogenesis include:
The Dearing strain of mammalian reovirus (T3D) has emerged as a leading oncolytic virus for cancer therapy. Reovirus selectively replicates in cells with an activated Ras signaling pathway, which is common in many cancers. This selectivity arises because Ras activation suppresses the double-stranded RNA-activated protein kinase R (PKR) pathway, allowing reovirus to overcome host antiviral defenses and replicate preferentially in malignant cells. Oncolytic reovirus has demonstrated safety and efficacy in clinical trials for various cancers, including melanoma, colorectal cancer, and head and neck squamous cell carcinoma. The virus is administered intratumorally or intravenously, with immune-mediated mechanisms contributing to antitumor activity. A proprietary formulation of reovirus (pelareorep) has been evaluated in multiple phase II and III trials.
The reovirus replication cycle and associated pathological outcomes are orchestrated by a set of viral proteins and host pathways that represent key molecular targets for therapeutic intervention and research.
| Key Molecular Targets | Details |
| TLR3 and TLR7/8 | Recognize dsRNA and ssRNA intermediates, leading to IRF3/7 activation and type I interferon production. |
| RIG-I andMDA5 | Cytoplasmic sensors that detect viral RNA and activate antiviral responses. |
| PKR (Protein kinase R) | Activated by dsRNA, PKR phosphorylates eIF2α, shutting down host protein synthesis. Reovirus counteracts PKR through σ3-mediated dsRNA sequestration and through the activation of Ras pathway, which inhibits PKR. |
In natural infections, reovirus pathogenesis involves several convergent pathways:
Reovirus stands at the intersection of fundamental virology and translational medicine. Its well-defined molecular biology, tractable genetics, and serotype-specific tropism have made it a model system for understanding viral pathogenesis, immune evasion, and the host response to dsRNA viruses. Simultaneously, its natural selectivity for Ras-transformed cells has positioned it as a leading oncolytic agent in cancer therapy. The molecular targets described—from the attachment protein σ1 to the polymerase λ3, from the immune evasion factor σ3 to the host Ras pathway—continue to inform both basic research and clinical development. As oncolytic reovirus advances through clinical trials and fundamental questions about viral persistence and immunopathology remain, reovirus will undoubtedly continue to serve as a versatile and valuable tool in virology and medicine.
Reference
| Target | Cat. No. | Product Name | Host | |
| Reovirus | DAG-WT5883 | Mouse reovirus Stock (Qualitative) | N/A | Inquiry |
| Reovirus | DAGC536 | Avian Reovirus (S1133) Chorioallantoic Membrane Homogenate | N/A | Inquiry |
| Reovirus | DAGC537 | Avian Reovirus (S1133) Tissue Culture | N/A | Inquiry |
| Reovirus | DAGA-2018 | Reovirus Serotype 3 (strain Abney) | LLC cells | Inquiry |
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