What a Difference a Gene Makes: Identification of Virulence Factors of Cowpox Virus

Cowpox Viruses: A Zoo Full of Viral Diversity and Lurking Threats

Cowpox viruses (CPXVs) exhibit the broadest known host range among the Poxviridae family and have caused lethal outbreaks in various zoo animals and pets across 12 Eurasian countries, as well as an increasing number of human cases. Herein, we review the history of how the cowpox name has evolved since the 1700s up to modern times. Despite early documentation of the different properties of CPXV isolates, only modern genetic analyses and phylogenies have revealed the existence of multiple Orthopoxvirus species that are currently constrained under the CPXV designation. We further chronicle modern outbreaks in zoos, domesticated animals, and humans, and describe animal models of experimental CPXV infections and how these can help shaping CPXV species distinctions. We also describe the pathogenesis of modern CPXV infections in animals and humans, the geographic range of CPXVs, and discuss CPXV-host interactions at the molecular level and their effects on pathogenicity and host range. Finally, we discuss the potential threat of these viruses and the future of CPXV research to provide a comprehensive review of CPXVs.

Molecular mimicry of NF-κB by vaccinia virus protein enables selective inhibition of antiviral responses

Infection of mammalian cells with viruses activates NF-κB to induce the expression of cytokines and chemokines and initiate an antiviral response. Here, we show that a vaccinia virus protein mimics the transactivation domain of the p65 subunit of NF-κB to inhibit selectively the expression of NF-κB-regulated genes. Using co-immunoprecipitation assays, we found that the vaccinia virus protein F14 associates with NF-κB co-activator CREB-binding protein (CBP) and disrupts the interaction between p65 and CBP. This abrogates CBP-mediated acetylation of p65, after which it reduces promoter recruitment of the transcriptional regulator BRD4 and diminishes stimulation of NF-κB-regulated genes CXCL10 and CCL2. Recruitment of BRD4 to the promoters of NFKBIA and CXCL8 remains unaffected by either F14 or JQ1 (a competitive inhibitor of BRD4 bromodomains), indicating that BRD4 recruitment is acetylation-independent. Unlike other viral proteins that are general antagonists of NF-κB, F14 is a selective inhibitor of NF-κB-dependent gene expression. An in vivo model of infection demonstrated that F14 promotes virulence. Molecular mimicry of NF-κB may be conserved because other orthopoxviruses, including variola, monkeypox and cowpox viruses, encode orthologues of F14.

Pathogenicity and virulence of hepatitis A virus

Hepatitis A is an acute infection of the liver, which is mostly asymptomatic in children and increases the severity with age. Although in most patients the infection resolves completely, in a few of them it may follow a prolonged or relapsed course or even a fulminant form. The reason for these different outcomes is unknown, but it is generally accepted that host factors such as the immunological status, age and the occurrence of underlaying hepatic diseases are the main determinants of the severity. However, it cannot be ruled out that some virus traits may also contribute to the severe clinical outcomes. In this review, we will analyze which genetic determinants of the virus may determine virulence, in the context of a paradigmatic virus in terms of its genomic, molecular, replicative, and evolutionary features.

Ectromelia-encoded virulence factor C15 specifically inhibits antigen presentation to CD4+ T cells post peptide loading

Smallpox and monkeypox pose severe threats to human health. Other orthopoxviruses are comparably virulent in their natural hosts, including ectromelia, the cause of mousepox. Disease severity is linked to an array of immunomodulatory proteins including the B22 family, which has homologs in all pathogenic orthopoxviruses but not attenuated vaccine strains. We demonstrate that the ectromelia B22 member, C15, is necessary and sufficient for selective inhibition of CD4+ but not CD8+ T cell activation by immunogenic peptide and superantigen. Inhibition is achieved not by down-regulation of surface MHC- II or co-stimulatory protein surface expression but rather by interference with antigen presentation. The appreciable outcome is interference with CD4+ T cell synapse formation as determined by imaging studies and lipid raft disruption. Consequently, CD4+ T cell activating stimulus shifts to uninfected antigen-presenting cells that have received antigen from infected cells. This work provides insight into the immunomodulatory strategies of orthopoxviruses by elucidating a mechanism for specific targeting of CD4+ T cell activation, reflecting the importance of this cell type in control of the virus.

In Vivo Characterization of a Bank Vole-Derived Cowpox Virus Isolate in Natural Hosts and the Rat Model

Cowpox virus (CPXV) belongs to the genus Orthopoxvirus in the Poxviridae family and is endemic in western Eurasia. Based on seroprevalence studies in different voles from continental Europe and UK, voles are suspected to be the major reservoir host. Recently, a CPXV was isolated from a bank vole (Myodes glareolus) in Germany that showed a high genetic similarity to another isolate originating from a Cotton-top tamarin (Saguinus oedipus). Here we characterize this first bank vole-derived CPXV isolate in comparison to the related tamarin-derived isolate. Both isolates grouped genetically within the provisionally called CPXV-like 3 clade. Previous phylogenetic analysis indicated that CPXV is polyphyletic and CPXV-like 3 clade represents probably a different species if categorized by the rules used for other orthopoxviruses. Experimental infection studies with bank voles, common voles (Microtusarvalis) and Wistar rats showed very clear differences. The bank vole isolate was avirulent in both common voles and Wistar rats with seroconversion seen only in the rats. In contrast, inoculated bank voles exhibited viral shedding and seroconversion for both tested CPXV isolates. In addition, bank voles infected with the tamarin-derived isolate experienced a marked weight loss. Our findings allow for the conclusion that CPXV isolates might differ in their replication capacity in different vole species and rats depending on their original host. Moreover, the results indicate host-specific differences concerning CPXV-specific virulence. Further experiments are needed to identify individual virulence and host factors involved in the susceptibility and outcome of CPXV-infections in the different reservoir hosts.