Myxoma virus and the Leporipoxviruses: an evolutionary paradigm

Evaluation of dried blood spots for serological surveys of myxoma and rabbit hemorrhagic disease viruses in their wild reservoir

Myxoma (MYXV) and rabbit hemorrhagic disease (RHDV) viruses are pathogens of economic relevance for cuniculture and conservation concern for wild European rabbits (Oryctolagus cuniculus), recently classified as 'Endangered' in its native range. Large-scale serological surveys, facilitated by sample collection using dried blood spots (DBS), allow monitoring seroprevalence in the wild reservoir but require evaluating the technique for the host and pathogen of interest. This study aimed to evaluate Protein Saver 903 DBS for MYXV and RHDV (genotype GI.2) serological surveys in European rabbits. Paired serum and DBS collected from 172 rabbits harvested or found dead in the Iberian Peninsula were tested for IgG antibodies specific against MYXV and RHDV GI.2 using indirect ELISA. We found an almost perfect agreement between serum and DBS for MYXV (Cohen's κ=0.914, CI95 0.847 - 0.981) and a strong agreement for RHDV GI.2 (Cohen's κ=0.808, CI95=0.722 - 0.893). The diagnostic sensitivity of DBS was 95.4 % (CI95 90.3 - 97.9 %) for MYXV and 82.1 % (CI95 73.2 - 88.5 %) for RHDV GI.2. The diagnostic specificity and positive predictive value were 100 % for both pathogens. This study supports DBS as a suitable sampling strategy for serological surveys of antibodies specific to MYXV and RHDV GI.2 in European rabbits, which generally agrees with results from other hosts and pathogens where this technique was evaluated.

Oncolytic viruses: a potential breakthrough immunotherapy for multiple myeloma patients

Oncolytic virotherapy represents an innovative and promising approach for the treatment of cancer, including multiple myeloma (MM), a currently incurable plasma cell (PC) neoplasm. Despite the advances that new therapies, particularly immunotherapy, have been made, relapses still occur in MM patients, highlighting the medical need for new treatment options. Oncolytic viruses (OVs) preferentially infect and destroy cancer cells, exerting a direct and/or indirect cytopathic effect, combined with a modulation of the tumor microenvironment leading to an activation of the immune system. Both naturally occurring and genetically modified viruses have demonstrated significant preclinical effects against MM cells. Currently, the OVs genetically modified measles virus strains, reovirus, and vesicular stomatitis virus are employed in clinical trials for MM. Nevertheless, significant challenges remain, including the efficiency of the virus delivery to the tumor, overcoming antiviral immune responses, and the specificity of the virus for MM cells. Different strategies are being explored to optimize OV therapy, including combining it with standard treatments and targeted therapies to enhance efficacy. This review will provide a comprehensive analysis of the mechanism of action of the different OVs, and preclinical and clinical evidence, focusing on the role of oncolytic virotherapy as a new possible immunotherapeutic approach also in combination with the current therapeutic armamentarium and underlying the future directions in the context of MM treatments.

Comparative analysis of two novel complete genomes of myxoma virus vaccine strains

Myxoma virus (MYXV) is a double-stranded DNA-containing virus of the family Poxviridae, genus Leporipoxvirus. MYXV is an important model virus for evolutionary and immunological research and a promising oncolytic. In this study, we sequenced and analyzed two complete genomes of MYXV virus vaccine strains B-82 and Rabbivac-B, which are widely used for vaccine production in Russia. Here, we first show that MYXV vaccine strains B-82 and Rabbivac-B share a common origin with the American recombinant MYXV MAV vaccine strain. In addition, our data suggest that the MYXV B-82 and Rabbivac-B strains contain a number of genes at the 5' and 3' ends that are identical to the virulent MYXV Lausanne strain. Several unique genetic signatures were identified in the M013L, M017L, M023, and M121R genes, helping to achieve high genetic resolution between vaccine strains. Overall, these findings highlight the evolutionary flexibility of certain genes in the MYXV genome and provide insights into the molecular epidemiology of the virus and subsequent vaccine development.

New Insights into Rabbit Viral Diseases

Viruses are responsible for many devastating rabbit diseases that impact their health and welfare and put their conservation and economic revenue at risk [...].

The RNA helicase DHX35 functions as a co-sensor for RIG-I-mediated innate immunity

RNA helicases are involved in the innate immune response against pathogens, including bacteria and viruses; however, their mechanism in the human airway epithelial cells is still not fully understood. Here, we demonstrated that DEAH (Asp-Glu-Ala-His) box polypeptide 35 (DHX35), a member of the DExD/H (Asp-Glu-x-Asp/His)-box helicase family, boosts antiviral innate immunity in human airway epithelial cells. DHX35 knockdown attenuated the production of interferon-β (IFN-β), IL6, and CXCL10, whereas DHX35 overexpression increased their production. Upon stimulation, DHX35 was constitutively expressed, but it translocated from the nucleus into the cytosol, where it recognized cytosolic poly(I:C) and poly(dA:dT) via its HELICc domain. Mitochondrial antiviral signaling protein (MAVS) acted as an adaptor for DHX35 and interacted with the HELICc domain of DHX35 using amino acids 360-510. Interestingly, DHX35 interacted with retinoic acid-inducible gene 1 (RIG-I), enhanced the binding affinity of RIG-I with poly(I:C) and poly(dA:dT), and formed a signalsome with MAVS to activate interferon regulatory factor 3 (IRF3), NF-κB-p65, and MAPK signaling pathways. These results indicate that DHX35 not only acted as a cytosolic nucleic acid sensor but also synergized with RIG-I to enhance antiviral immunity in human airway epithelial cells. Our results demonstrate a novel molecular mechanism for DHX35 in RIG-I-mediated innate immunity and provide a novel candidate for drug and vaccine design to control viral infections in the human airway.

Identification and Characterisation of a Myxoma Virus Detected in the Italian Hare (Lepus corsicanus)

Myxoma virus (MYXV) is a Leporipoxvirus (genus) belonging to the family Poxviridae; it is characterised by a genome of approximately 161 kb dsDNA encoding for several proteins that play an essential role in both host spectrum determination and immunomodulation. The healthy reservoir of the virus is Sylvilagus spp. At the same time, in wild and domestic European rabbits (Oryctolagus cuniculus), MYXV is the etiologic agent of myxomatosis, a disease with an extremely high mortality rate. In 2014, an interspecies jump of MYXV was reported in Lepus europaeus in the UK. In 2018, myxomatosis induced by a new recombinant strain called MYXV-To was identified during a large outbreak in Iberian hares (Lepus granatensis) in Spain. Here, we describe the case of myxomatosis in another hare species: an adult male Italian hare (Lepus corsicanus) found dead in 2018 in Sicily with lesions suggestive of myxomatosis and treponema infection. Laboratory tests, e.g., end-point PCR and negative staining electron microscopy, confirmed the presence of both pathogens. MYXV was then isolated from tissue samples in permissive cells and sequenced using NGS technology. Main genomic differences concerning known MYXV strains are discussed.

Microbial Therapy and Breast Cancer Management: Exploring Mechanisms, Clinical Efficacy, and Integration within the One Health Approach

This comprehensive review elucidates the profound relationship between the human microbiome and breast cancer management. Recent findings highlight the significance of microbial alterations in tissue, such as the gut and the breast, and their role in influencing the breast cancer risk, development, progression, and treatment outcomes. We delve into how the gut microbiome can modulate systemic inflammatory responses and estrogen levels, thereby impacting cancer initiation and therapeutic drug efficacy. Furthermore, we explore the unique microbial diversity within breast tissue, indicating potential imbalances brought about by cancer and highlighting specific microbes as promising therapeutic targets. Emphasizing a holistic One Health approach, this review underscores the importance of integrating insights from human, animal, and environmental health to gain a deeper understanding of the complex microbe-cancer interplay. As the field advances, the strategic manipulation of the microbiome and its metabolites presents innovative prospects for the enhancement of cancer diagnostics and therapeutics. However, rigorous clinical trials remain essential to confirm the potential of microbiota-based interventions in breast cancer management.

Quantifying resistance to myxomatosis in wild rabbits produces novel evolutionary insights

Wild rabbits in Australia developed genetic resistance to the myxoma virus, which was introduced as a biological control agent. However, little is known about the rate at which this evolutionary change occurred. We collated data from challenge trials that estimated rabbit resistance to myxomatosis in Australia and expressed resistance on a continuous scale, enabling trends in its development to be assessed over 45 years up to 1995. Resistance initially increased rapidly, followed by a plateau lasting ten years, before a second rapid increase occurred associated with the introduction of European rabbit fleas as myxoma virus vectors. By contrast, in the United Kingdom, where rabbit flea vectors were already present when the myxoma virus initially spread, resistance developed more slowly. No estimates of rabbit resistance to myxomatosis have been made for almost 30 years, despite other highly lethal rabbit pathogens becoming established worldwide. Continued testing of wild-caught rabbits in Australia to determine current levels of resistance to myxomatosis is recommended to assess its current effectiveness for managing pest rabbits. Given the economic and environmental significance of invasive rabbits, it would be remiss to manage such biological resources and ecosystem services poorly.

Evolution and diversity of nucleotide and dinucleotide composition in poxviruses

Poxviruses (family Poxviridae) have long dsDNA genomes and infect a wide range of hosts, including insects, birds, reptiles and mammals. These viruses have substantial incidence, prevalence and disease burden in humans and in other animals. Nucleotide and dinucleotide composition, mostly CpG and TpA, have been largely studied in viral genomes because of their evolutionary and functional implications. We analysed here the nucleotide and dinucleotide composition, as well as codon usage bias, of a set of representative poxvirus genomes, with a very diverse host spectrum. After correcting for overall nucleotide composition, entomopoxviruses displayed low overall GC content, no enrichment in TpA and large variation in CpG enrichment, while chordopoxviruses showed large variation in nucleotide composition, no obvious depletion in CpG and a weak trend for TpA depletion in GC-rich genomes. Overall, intergenome variation in dinucleotide composition in poxviruses is largely accounted for by variation in overall genomic GC levels. Nonetheless, using vaccinia virus as a model, we found that genes expressed at the earliest times in infection are more CpG-depleted than genes expressed at later stages. This observation has parallels in betahepesviruses (also large dsDNA viruses) and suggests an antiviral role for the innate immune system (e.g. via the zinc-finger antiviral protein ZAP) in the early phases of poxvirus infection. We also analysed codon usage bias in poxviruses and we observed that it is mostly determined by genomic GC content, and that stratification after host taxonomy does not contribute to explaining codon usage bias diversity. By analysis of within-species diversity, we show that genomic GC content is the result of mutational biases. Poxvirus genomes that encode a DNA ligase are significantly AT-richer than those that do not, suggesting that DNA repair systems shape mutation biases. Our data shed light on the evolution of poxviruses and inform strategies for their genetic manipulation for therapeutic purposes.

Dual-Armed Oncolytic Myxoma Virus Encoding IFN-γ and CD47 Promotes Lymphocyte Infiltration and Tumor Suppression of Syngeneic Murine Melanoma

Myxoma virus (MyxV) is a rabbit-specific poxvirus. However, its ability to selectively target tumor cells has established it as a safe and effective anticancer therapy. To strengthen its preclinical efficacy, transgenes that can prolong cancer cell infection and enhance anti-tumor effector functions are currently being investigated. We engineered MyxV armed with CD47, to turn on a 'do not eat me' signal within infected cells with actively replicating viruses, and with IFN-γ to further activate host immune anticancer responses. Tumor suppressive activities were significantly enhanced by the dual-armed MyxV_CD47/IFN-γ compared to parental MyxV or single-armed MyxV_CD47 or MyxV_IFN-γ. In addition, significant increases in IFN-γ+ CD8+T-cells and CD4+ T-cells populations within tumor-infiltrating lymphocytes (TIL) were observed after MyxV_CD47/IFN-γ treatment. Notably, all groups treated with MyxV showed a marked reduction in Foxp3+ CD4+ regulatory T-cells (Tregs) within TIL. We also show that MyxV infection induces PD-L1 up-regulation in cancer cells, and combinational treatment of MyxV with anti-mouse PD-L1 antibodies (αPD-L1) further controlled tumor burden and increased survival in the syngeneic melanoma model B16F10. Our data demonstrate that a CD47 and IFNγ dual-armed MyxV is an effective oncolytic viral immunotherapeutic. These findings strongly support further preclinical investigations to develop next-generation MyxV-based immunotherapy approaches.

Do pathogens always evolve to be less virulent? The virulence–transmission trade-off in light of the COVID-19 pandemic

The direction the evolution of virulence takes in connection with any pathogen is a long-standing question. Formerly, it was theorized that pathogens should always evolve to be less virulent. As observations were not in line with this theoretical outcome, new theories emerged, chief among them the transmission–virulence trade-off hypotheses, which predicts an intermediate level of virulence as the endpoint of evolution. At the moment, we are very much interested in the future evolution of COVID-19’s virulence. Here, we show that the disease does not fulfill all the assumptions of the hypothesis. In the case of COVID-19, a higher viral load does not mean a higher risk of death; immunity is not long-lasting; other hosts can act as reservoirs for the virus; and death as a consequence of viral infection does not shorten the infectious period. Consequently, we cannot predict the short- or long-term evolution of the virulence of COVID-19.

Pathological changes and viral antigen distribution in tissues of Iberian hare (Lepus granatensis) naturally infected with the emerging recombinant myxoma virus (ha-MYXV)

BACKGROUND

A cross-species jump was confirmed in 2018, when a novel recombinant myxoma virus (MYXV) (ha-MYXV) caused high mortality in Iberian hare (Lepus granatensis) in the Iberian Peninsula.

METHOD

The aim of this study was to evaluate the main lesions, tissular distribution and target cells of ha-MYXV in Iberian hare. Gross postmortem examinations and histological and immunohistochemical studies to detect ha-MYXV were carried out in 28 animals that were confirmed as ha-MYXV positive by PCR.

RESULTS

The main macroscopic lesions were bilateral blepharoconjunctivitis, epistaxis, intense congestion and oedema in several organs and some internal haemorrhages. Visible myxomas were not found. Histopathological examination revealed hyperplastic epidermis with predominant hyperkeratosis and myxoid matrix in the dermis. ha-MYXV-positive keratinocytes showed hydropic degeneration and cytoplasmic inclusion bodies. Alveolar oedema, interstitial pneumonia, dramatic lymphoid depletion in the spleen and necrosis in the liver and testis were observed. ha-MYXV was mainly detected in epithelial and myxoma cells in the skin, and also in macrophages, lymphocytes, fibroblasts and endothelial cells in several organs, as well as in hepatocytes and Leydig cells.

LIMITATIONS

A non-homogeneous number of samples were included in all the animals. Future experimental studies with controlled variables are necessary.

CONCLUSION

These findings correspond to an unusual form of myxomatosis, characterised by an acute or hyperacute presentation.

Molecular genotyping, histopathological and immunohistochemical studies of bovine papillomatosis

Background

Bovine papillomatosis (BP) is considered the most common health problem in large cattle farms.

Aim

This study attempts to confirm clinically suspected BP in cattle by polymerase chain reaction (PCR) assay, histopathology, immunohistochemistry (IHC), and genotyping analysis of local isolates.

Methods

According to morphological appearance and lesion features, a cross sectional study of 54 clinically diagnosed BP cattle was assigned to this current investigation from May to August (2021) in Al-Kut district (Wasit Province, Iraq) private veterinary clinics using purposive sampling technique based on set criteria. The cattle were diagnosed clinically, and the tissues were collected and some fixed in 10% neutral buffered formalin and other stored frozen and examined by histopathological technique, IHC, and PCR assays.

Results

Using PCR assay, all cattle were positive for the BPV L1 gene. According to detect the L1 gene, analysis of the phylogenetic tree showed that local BPV cattle isolates were closely related to the NCBI-BLAST BPV type-1 and type-2 of the Polish equine isolate (KF284133.1) and BPV Brazilian Bostaurus isolate (MH187961.1), respectively. Histological detection showed there were acanthosis, hyperkeratosis, epidermal thickening, severe infiltration of mononuclear cells, massive hemorrhage, dermal fibroplasias, multifocal spongiosis, moderate neovascularization, moderate to severe elongation of the retention ridge towards the dermis, parakeratosis, rings of calcification, and necrosis with nuclear pyknosis of some spinosum cells. Immunohistochemical findings of tumor necrosis factor-alpha, epidermal growth factor receptor and Fascin showed a significant variation in values of immunoreaction in the dermis and epidermis. These results ranged from negative (0) to mild positive (+1) to moderate positive (+2) reactions.

Conclusion

The study provided essential molecular and genotyping data to improve our knowledge by emphasizing the crucial of IHC as an elegant diagnostic method to detect cellular alterations.

Retrospective serological and molecular survey of myxoma or antigenically related virus in the Iberian hare, Lepus granatensis

The 2018 outbreak of myxomatosis in the Iberian hare (Lepus granatensis) has been hypothesized to originate from a species jump of the rabbit-associated myxoma virus (MYXV), after natural recombination with an unknown poxvirus. Iberian hares were long considered resistant to myxomatosis as no prior outbreaks were reported. To provide insights into the emergence of this recombinant virus (ha-MYXV), we investigated serum samples from 451 Iberian hares collected over two time periods almost two decades apart, 1994-1999 and 2017-2019 for the presence of antibodies and MYXV-DNA. First, we screened all serum samples using a rabbit commercial indirect ELISA (iELISA) and then tested a subset of these samples in parallel using indirect immunofluorescence test (IFT), competitive ELISA (cELISA) and qPCR targeting M000.5L/R gene conserved in MYXV and ha-MYXV. The cut-off of iELISA relative index 10 = 6.1 was selected from a semiparametric finite mixture analysis aiming to minimize the probability of false positive results. Overall, MYXV related-antibodies were detected in 57 hares (12.6%) including 38 apparently healthy hares (n = 10, sampled in 1994-1999, none MYXV-DNA positive, and n = 28 sampled in 2017-2019 of which four were also ha-MYXV-DNA positive) and 19 found-dead and ha-MYXV-DNA-positive sampled in 2018-2019. Interestingly, four seronegative hares sampled in 1997 were MYXV-DNA positive by qPCR, the result being confirmed by sequencing of three of them. For the Iberian hares hunted or live trapped (both apparently health), seroprevalence was significantly higher in 2017-2019 (13.0%, CI95% 9.2-18.2%) than in 1994-1999 (5.4%, CI95% 3.0-9.6%) (p = .009). Within the second period, seroprevalence was significantly higher in 2019 compared to 2017 (24.7 vs 1.7% considering all the sample, p = .007), and lower during the winter than the autumn (p < .001). While our molecular and serological results show that Iberian hares have been in contact with MYXV or an antigenically similar virus at least since 1996, they also show an increase in seroprevalence in 2018-2019. The remote contact with MYXV may have occurred with strains that circulated in rabbits, or with unnoticed strains already circulating in Iberian hare populations. This work strongly suggests the infection of Iberian hares with MYXV or an antigenically related virus, at least 20 years before the severe virus outbreaks were registered in 2018.

Spatiotemporal monitoring of myxomatosis in European wild rabbit (Oryctolagus cuniculus) in Spanish Mediterranean ecosystems

A long-term active epidemiological surveillance programme was conducted to determine seroprevalence to myxoma virus (MYXV), infection prevalence and spatiotemporal patterns and factors associated with MYXV circulation in wild rabbits (Oryctolagus cuniculus) in Spanish Mediterranean ecosystems. A total of 2376 animals were sampled over four study periods: 2009-2012 (P1), 2012-2015 (P2), 2015-2018 (P3) and 2018-2021 (P4). Antibodies against MYXV were detected by a commercial indirect ELISA in 59.9% (1424/2376; 95% CI: 58.0-61.9) of wild rabbits. At least one seropositive animal was detected on 131 (96.3%) of 136 game estates sampled. MYXV infection was confirmed by PCR in 94 of 1063 (8.8%; 95% CI: 7.3-10.7) wild rabbits. Circulation of the novel recombinant MYXV (ha-MYXV) was not found in wild rabbits analysed during P4. Five statistically significant spatiotemporal clusters of high MYXV seroprevalence were identified using a Bernoulli model: one in P2 and four in P3. A generalized linear mixed model (GLMM) analysis identified sampling season (autumn), age (adult and juvenile), outbreaks of myxomatosis in the month prior to sampling, mean annual temperature, humidity and seropositivity to rabbit haemorrhagic disease virus as factors potentially linked with MYXV seropositivity. GLMM analysis identified outbreaks of myxomatosis in the month prior to sampling, MYXV seropositivity and presence of lesions compatible with myxomatosis as factors associated with MYXV infection. The results indicate high exposure, widespread but non-homogeneous distribution, and endemic circulation of MYXV in wild rabbit populations in southern Spain during the last decade. Prevalence of antibodies against MYXV showed fluctuations both within the year and over the study periods, revealing variations in the immunity of wild rabbit populations in Mediterranean ecosystems that could increase the risk of MYXV re-emergence in immunologically naïve populations. The present study highlights the importance of long-term surveillance to better understand the epidemiology of MYXV in wild lagomorphs.

Capripoxviruses, leporipoxviruses, and orthopoxviruses: Occurrences of recombination

Poxviruses are double-stranded DNA viruses with several members displaying restricted host ranges. They are genetically stable with low nucleotide mutation rates compared to other viruses, due to the poxviral high-fidelity DNA polymerase. Despite the low accumulation of mutations per replication cycle, poxvirus genomes can recombine with each other to generate genetically rearranged viruses through recombination, a process directly associated with replication and the aforementioned DNA polymerase. Orthopoxvirus replication is intimately tethered to high frequencies of homologous recombination between co-infecting viruses, duplicated sequences of the same virus, and plasmid DNA transfected into poxvirus-infected cells. Unfortunately, the effect of these genomic alterations on the cellular context for all poxviruses across the family Poxviridae remains elusive. However, emerging sequence data on currently circulating and archived poxviruses, such as the genera orthopoxviruses and capripoxviruses, display a wide degree of divergence. This genetic variability cannot be explained by clonality or genetic drift alone, but are probably a result of significant genomic alterations, such as homologous recombination, gene loss and gain, or gene duplications as the major selection forces acting on viral progeny. The objective of this review is to cross-sectionally overview the currently available findings on natural and laboratory observations of recombination in orthopoxviruses, capripoxviruses, and leporipoxviruses, as well as the possible mechanisms involved. Overall, the reviewed available evidence allows us to conclude that the current state of knowledge is limited in terms of the relevance of genetic variations across even a genus of poxviruses as well as fundamental features governing and precipitating intrinsic gene flow and recombination events.

Divergent Evolutionary Pathways of Myxoma Virus in Australia: Virulence Phenotypes in Susceptible and Partially Resistant Rabbits Indicate Possible Selection for Transmissibility

To characterize the ongoing evolution of myxoma virus in Australian rabbits, we used experimental infections of laboratory rabbits to determine the virulence and disease phenotypes of recent virus isolates. The viruses, collected between 2012 and 2015, fell into three lineages, one of which, lineage c, experienced a punctuated increase in evolutionary rate. All viruses were capable of causing acute death with aspects of neutropenic septicemia, characterized by minimal signs of myxomatosis, the occurrence of pulmonary edema and bacteria invasions throughout internal organs, but with no inflammatory response. For the viruses of highest virulence all rabbits usually died at this point. In more attenuated viruses, some rabbits died acutely, while others developed an amyxomatous phenotype. Rabbits that survived for longer periods developed greatly swollen cutaneous tissues with very high virus titers. This was particularly true of lineage c viruses. Unexpectedly, we identified a line of laboratory rabbits with some innate resistance to myxomatosis and used these in direct comparisons with the fully susceptible rabbit line. Importantly, the same disease phenotype occurred in both susceptible and resistant rabbits, although virulence was shifted toward more attenuated grades in resistant animals. We propose that selection against inflammation at cutaneous sites prolongs virus replication and enhances transmission, leading to the amyxomatous phenotype. In some virus backgrounds this creates an immunosuppressive state that predisposes to high virulence and acute death. The alterations in disease pathogenesis, particularly the overwhelming bacterial invasions that characterize the modern viruses, suggest that their virulence grades are not directly comparable with earlier studies.

IMPORTANCE The evolution of the myxoma virus (MYXV) following its release as a biological control for European rabbits in Australia is the textbook example of the coevolution of virus virulence and host resistance. However, most of our knowledge of MYXV evolution only covers the first few decades of its spread in Australia and often with little direct connection between how changes in virus phenotype relate to those in the underlying virus genotype. By conducting detailed experimental infections of recent isolates of MYXV in different lines of laboratory rabbits, we examined the ongoing evolution of MYXV disease phenotypes. Our results reveal a wide range of phenotypes, including an amyxomatous type, as well as the impact of invasive bacteria, that in part depended on the level of rabbit host resistance. These results provide a unique insight into the complex virus and host factors that combine to shape disease phenotype and viral evolution.

Pathogen-derived peptides in drug targeting and its therapeutic approach

Peptides, short stretches of amino acids or small proteins that occupy a strategic position between proteins and amino acids, are readily accessible by chemical and biological methods. With ideal properties for forming high-affinity and specific interactions with host target proteins, they have established an important niche in the drug development spectrum complementing small molecule and biological therapeutics. Among the most successful biomedicines in use today, peptide-based drugs show great promise. This, coupled with recent advances in synthetic and nanochemical biology, has led to the creation of tailor-made peptide therapeutics for improved biocompatibility. This review presents an overview of the latest research on pathogen-derived, host-cell-interacting peptides. It also highlights strategies for using peptide-based therapeutics that address cellular transport challenges through the introduction of nanoparticles that serve as platforms to facilitate the delivery of peptide biologics and therapeutics for treating various inflammatory diseases. Finally, this paper describes future perspectives, specific pathogen-based peptides that can enhance specificity, efficiency, and capacity in functional peptide-based therapeutics, which are in the spotlight as new treatment alternatives for various diseases, and also presents verified sequences and targets that can increase chemical and pharmacological value.

The past, current and future epidemiological dynamic of SARS-CoV-2

SARS-CoV-2, the agent of the COVID-19 pandemic, emerged in late 2019 in China, and rapidly spread throughout the world to reach all continents. As the virus expanded in its novel human host, viral lineages diversified through the accumulation of around two mutations a month on average. Different viral lineages have replaced each other since the start of the pandemic, with the most successful Alpha, Delta and Omicron variants of concern (VoCs) sequentially sweeping through the world to reach high global prevalence. Neither Alpha nor Delta was characterized by strong immune escape, with their success coming mainly from their higher transmissibility. Omicron is far more prone to immune evasion and spread primarily due to its increased ability to (re-)infect hosts with prior immunity. As host immunity reaches high levels globally through vaccination and prior infection, the epidemic is expected to transition from a pandemic regime to an endemic one where seasonality and waning host immunization are anticipated to become the primary forces shaping future SARS-CoV-2 lineage dynamics. In this review, we consider a body of evidence on the origins, host tropism, epidemiology, genomic and immunogenetic evolution of SARS-CoV-2 including an assessment of other coronaviruses infecting humans. Considering what is known so far, we conclude by delineating scenarios for the future dynamic of SARS-CoV-2, ranging from the good-circulation of a fifth endemic 'common cold' coronavirus of potentially low virulence, the bad-a situation roughly comparable with seasonal flu, and the ugly-extensive diversification into serotypes with long-term high-level endemicity.

Metatranscriptomics Analysis Reveals Diverse Viral RNA in Cutaneous Papillomatous Lesions of Cattle

Bovine papillomavirus (BPV) is associated with bovine papillomatosis, a disease that forms benign warts in epithelial tissues, as well as malignant lesions. Previous studies have detected a co-infection between BPV and other viruses, making it likely that these co-infections could influence disease progression. Therefore, this study aimed to identify and annotate viral genes in cutaneous papillomatous lesions of cattle. Sequences were obtained from the GEO database, and an RNA-seq computational pipeline was used to analyze 3 libraries from bovine papillomatous lesions. In total, 25 viral families were identified, including Poxviridae, Retroviridae, and Herpesviridae. All libraries shared similarities in the viruses and genes found. The viral genes shared similarities with BPV genes, especially for functions as virion entry pathway, malignant progression by apoptosis suppression and immune system control. Therefore, this study presents relevant data extending the current knowledge regarding the viral microbiome in BPV lesions and how other viruses could affect this disease.

When viruses become more virulent

[Figure: see text].

International Harmonization of Nomenclature and Diagnostic Criteria (INHAND): Nonproliferative and Proliferative Lesions of the Rabbit

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions Project (www.toxpath.org/inhand.asp) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP) and North America (STP) to develop an internationally accepted nomenclature for proliferative and non-proliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying microscopic lesions observed in most tissues and organs from the laboratory rabbit used in nonclinical safety studies. Some of the lesions are illustrated by color photomicrographs. The standardized nomenclature presented in this document is also available electronically on the internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous lesions as well as lesions induced by exposure to test materials. Relevant infectious and parasitic lesions are included as well. A widely accepted and utilized international harmonization of nomenclature for lesions in laboratory animals will provide a common language among regulatory and scientific research organizations in different countries and increase and enrich international exchanges of information among toxicologists and pathologists.

Detection of Myxoma Virus DNA in Ticks from Lagomorph Species in Spain Suggests Their Possible Role as Competent Vector in Viral Transmission

Myxoma virus (MYXV) causes morbidity and mortality in European wild rabbits (Oryctolagus cuniculus) worldwide, and recently in Iberian hares (Lepus granatensis) in Spain. We aimed to assess the presence of MYXV-specific DNA in ixodid ticks collected from both hosts. A total of 417 ticks harvested from 30 wild lagomorphs, including wild rabbits and Iberian hares were collected from southern Spain. Enzyme-linked immunosorbent assay and PCR-sequencing were used to detect virus exposure and presence, respectively. Antibodies to MYXV were detected in 68% (17/25) of wild rabbits and in 67% (2/3) of Iberian hares. We detected MYXV DNA in 50.7% of pools of two different tick species (nymphs and adults of Rhipicephalus pusillus, and nymphs of Hyalomma lusitanicum) parasitizing rabbits and hares. The obtained partial sequence of the viral major envelope protein gene showed a mutation (G383A) within the MYXV_gp026 locus between the rabbit strain and Iberian hare strain (recently isolated in tissues of infected hares from Spain). However, in our study, the viral DNA presence was detected for the first time using tick DNA as the PCR-template, but the possible role of ticks as vectors of MYXV still needs to be elucidated.

Viruses for Landscape-Scale Therapy: Biological Control of Rabbits in Australia

Viral diseases, whether of animals or humans, are normally considered as problems to be managed. However, in Australia, two viruses have been used as landscape-scale therapeutics to control European rabbits (Oryctolagus cuniculus), the preeminent invasive vertebrate pest species. Rabbits have caused major environmental and agricultural losses and contributed to extinction of native species. It was not until the introduction of Myxoma virus that effective control of this pest was obtained at a continental scale. Subsequent coevolution of rabbit and virus saw a gradual reduction in the effectiveness of biological control that was partially ameliorated by the introduction of the European rabbit flea to act as an additional vector for the virus. In 1995, a completely different virus, Rabbit hemorrhagic disease virus (RHDV), escaped from testing and spread through the Australian rabbit population and again significantly reduced rabbit numbers and environmental impacts. The evolutionary pressures on this virus appear to be producing quite different outcomes to those that occurred with myxoma virus and the emergence and invasion of a novel genotype of RHDV in 2014 have further augmented control. Molecular studies on myxoma virus have demonstrated multiple proteins that manipulate the host innate and adaptive immune response; however the molecular basis of virus attenuation and reversion to virulence are not yet understood.

Genomic insights into a population of introduced European rabbits Oryctolagus cuniculus in Australia and the development of genetic resistance to rabbit hemorrhagic disease virus

The European rabbit (Oryctolagus cuniculus) is one of the most devastating invasive species in Australia. Since the 1950s, myxoma virus (MYXV) and rabbit haemorrhagic disease virus (RHDV) have been used to manage overabundant rabbit populations. Resistance to MYXV was observed within a few years of the release. More recently, resistance to lethal RHDV infection has also been reported, undermining the efficiency of landscape-scale rabbit control. Previous studies suggest that genetic resistance to lethal RHDV infection may differ locally between populations, yet the mechanisms of genetic resistance remain poorly understood. Here, we used genotyping by sequencing (GBS) data representing a reduced representation of the genome, to investigate Australian rabbit populations. Our aims were to understand the relationship between populations and identify possible genomic signatures of selection for RHDV resistance. One population we investigated had previously been reported to show levels of resistance to lethal RHDV infection. This population was compared to three other populations with lower or no previously reported RHDV resistance. We identified a set of novel candidate genes that could be involved in host-pathogen interactions such as virus binding and infection processes. These genes did not overlap with previous studies on RHDV resistance carried out in different rabbit populations, suggesting that multiple mechanisms are feasible. These findings provide useful insights into the different potential mechanisms of genetic resistance to RHDV virus which will inform future functional studies in this area.

Experimental evidence for stabilizing selection on virulence in a bacterial pathogen

The virulence‐transmission trade‐off hypothesis has provided a dominant theoretical basis for predicting pathogen virulence evolution, but empirical tests are rare, particularly at pathogen emergence. The central prediction of this hypothesis is that pathogen fitness is maximized at intermediate virulence due to a trade‐off between infection duration and transmission rate. However, obtaining sufficient numbers of pathogen isolates of contrasting virulence to test the shape of relationships between key pathogen traits, and doing so without the confounds of evolved host protective immunity (as expected at emergence), is challenging. Here, we inoculated 55 isolates of the bacterial pathogen, Mycoplasma gallisepticum, into non‐resistant house finches (Haemorhous mexicanus) from populations that have never been exposed to the disease. Isolates were collected over a 20‐year period from outbreak in disease‐exposed populations of house finches and vary markedly in virulence. We found a positive linear relationship between pathogen virulence and transmission rate to an uninfected sentinel, supporting the core assumption of the trade‐off hypothesis. Further, in support of the key prediction, there was no evidence for directional selection on a quantitative proxy of pathogen virulence and, instead, isolates of intermediate virulence were fittest. Surprisingly, however, the positive relationship between virulence and transmission rate was not underpinned by variation in pathogen load or replication rate as is commonly assumed. Our results indicate that selection favors pathogens of intermediate virulence at disease emergence in a novel host species, even when virulence and transmission are not linked to pathogen load.

Fleas and flea-borne diseases of North Africa

North Africa has an interesting and rich wildlife including hematophagous arthropods, and specifically fleas, which constitute a large part of the North African fauna, and are recognised vectors of several zoonotic bacteria. Flea-borne organisms are widely distributed throughout the world in endemic disease foci, where components of the enzootic cycle are present. Furthermore, flea-borne diseases could re-emerge in epidemic form because of changes in the vector-host ecology due to environmental and human behaviour modifications. We need to know the real incidences of flea-borne diseases in the world due to this incidence could be much greater than are generally recognized by physicians and health authorities. As a result, diagnosis and treatment are often delayed by health care professionals who are unaware of the presence of these infections and thus do not take them into consideration when attempting to determine the cause of a patient's illness. In this context, this bibliographic review aims to summarise the main species of fleas present in North Africa, their geographical distribution, flea-borne diseases, and their possible re-emergence.

RNA helicase A as co-factor for DNA viruses during replication

RNA helicase A (RHA) is a ubiquitously expressed DExH-box helicase enzyme that is involved in a wide range of biological processes including transcription, translation, and RNA processing. A number of RNA viruses recruit RHA to the viral RNA to facilitate virus replication. DNA viruses contain a DNA genome and replicate using a DNA-dependent DNA polymerase. RHA has also been reported to associate with some DNA viruses during replication, in which the enzyme acts on the viral RNA or protein products. As shown for Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus, RHA has potential to allow the virus to control a switch in cellular gene expression to modulate the antiviral response. While the study of the interaction of RHA with DNA viruses is still at an early stage, preliminary evidence indicates that the underlying molecular mechanisms are diverse. We now review the current status of this emerging field.

Detection of recombinant Hare Myxoma Virus in wild rabbits (Oryctolagus cuniculus algirus)

In late 2018, an epidemic myxomatosis outbreak emerged on the Iberian Peninsula leading to high mortality in Iberian hare populations. A recombinant Myxoma virus (strains MYXV-Tol and ha-MYXV) was rapidly identified, harbouring a 2.8 kbp insertion containing evolved duplicates of M060L, M061L, M064L, and M065L genes from myxoma virus (MYXV) or other Poxviruses. Since 2017, 1616 rabbits and 125 hares were tested by a qPCR directed to M000.5L/R gene, conserved in MYXV and MYXV-Tol/ha-MYXV strains. A subset of the positive samples (20%) from both species was tested for the insert with MYXV being detected in rabbits and the recombinant MYXV in hares. Recently, three wild rabbits were found dead South of mainland Portugal, showing skin oedema and pulmonary lesions that tested positive for the 2.8 kbp insert. Sequencing analysis showed 100% similarity with the insert sequences described in Iberian hares from Spain. Viral particles were observed in the lungs and eyelids of rabbits by electron microscopy, and isolation in RK13 cells attested virus infectivity. Despite that the analysis of complete genomes may predict the recombinant MYXV strains’ ability to infect rabbit, routine analyses showed species segregation for the circulation of MYXV and recombinant MYXV in wild rabbit and in Iberian hares, respectively. This study demonstrates, however, that recombinant MYXV can effectively infect and cause myxomatosis in wild rabbits and domestic rabbits, raising serious concerns for the future of the Iberian wild leporids while emphasises the need for the continuous monitoring of MYXV and recombinant MYXV in both species.

Monitoring of emerging myxoma virus epidemics in Iberian hares (Lepus granatensis) in Spain, 2018-2020

Myxomatosis is an infectious disease caused by the myxoma virus (MYXV), which has very high mortality rates in European wild rabbits (Oryctolagus cuniculus). While sporadic cases of myxomatosis have also been reported in some hare species, these lagomorphs are considered to have a low susceptibility to MYXV infection. In the present study, we describe the spatiotemporal evolution and main epidemiological findings of novel hare MYXV (ha-MYXV or MYXV-Tol) epidemics in Iberian hares (Lepus granatensis) in Spain. In the period 2018-2020, a total of 487 hares from 372 affected areas were confirmed to be MYXV-infected by PCR. ha-MYXV outbreaks were detected in most of the Spanish regions where the Iberian hare is present. The spatial distribution was not homogeneous, with most outbreaks concentrated in the southern and central parts of Spain. Consecutive outbreaks reported in the last two years suggest endemic circulation in Spain of this emerging virus. A retrospective study carried out just after the first epidemic period (2018-2019) revealed that the virus could have been circulating since June 2018. The number of outbreaks started to rise in July, peaked during the first half of August and October and then decreased sharply until January 2019. The apparent mean mortality rate was 55.4% (median: 70%). The results indicated high susceptibility of the Iberian hare to ha-MYXV infection, but apparent resistance in the sympatric hare species present in Spain and less infectivity in European rabbits. The novel ha-MYXV has had significant consequences on the health status of Iberian hare populations in Spain, which is of animal health and conservation concern. The present study contributes to a better understanding of ha-MYXV emergence and will provide valuable information for the development of control strategies. Further research is warranted to assess the impact of this emerging virus on wild lagomorph populations and to elucidate its ecological implications for Iberian Mediterranean ecosystems.

Novel Trivalent Vectored Vaccine for Control of Myxomatosis and Disease Caused by Classical and a New Genotype of Rabbit Haemorrhagic Disease Virus

Myxoma virus (MV) and rabbit haemorrhagic disease virus (RHDV) are the major causes of lethal viral diseases in the European rabbit. In 2010, a new RHDV genotype (RHDV2) emerged in the field that had limited cross-protection with the classical RHDV (RHDV1). For optimal protection of rabbits and preventing spread of disease, a vaccine providing protection against all three key viruses would be ideal. Therefore, a novel trivalent myxoma vectored RHDV vaccine (Nobivac Myxo-RHD PLUS) was developed similar to the existing bivalent myxoma vectored RHDV vaccine Nobivac Myxo-RHD. The new vaccine contains the Myxo-RHDV1 strain already included in Nobivac Myxo-RHD and a similarly produced Myxo-RHDV2 strain. This paper describes several key safety and efficacy studies conducted for European licensing purposes. Nobivac Myxo-RHD PLUS showed to be safe for use in rabbits from five weeks of age onwards, including pregnant rabbits, and did not spread from vaccinated rabbits to in-contact controls. Furthermore, protection to RHDV1 and RHDV2 was demonstrated by challenge, while the serological response to MV was similar to that after vaccination with Nobivac Myxo-RHD. Therefore, routine vaccination with Nobivac Myxo-RHD PLUS can prevent the kept rabbit population from these major viral diseases.

Biocontrol of the Common Carp (Cyprinus carpio) in Australia: A Review and Future Directions

Invasive pest species are recognized as one of the important drivers of reduced global biodiversity. In Australia, the 267 invasive plant, animal and microbial species, established since European colonization in the 1770s, have been unequivocally declared the most important threat to species diversity in this country. One invasive pest, the common carp (Cyprinus carpio), has been targeted in an integrated pest management plan that might include cyprinid herpesvirus 3 (CyHV-3) as a potential biocontrol agent. The species-specificity of the released virus (and of field variants that will inevitably arise) has been assessed, and the virus judged to be safe. It has also been hypothesised that, because the virulence of the CyHV-3 will likely decline following release, the virus should be used strategically: initially, the aim would be to markedly reduce numbers of carp in naive populations, and then some other, as yet uncertain, complementary broad-scale control measure would knock-down carp numbers even further. Brief results are included from recent studies on the modelling of release and spread of the virus, the ecological and social concerns associated with virus release, and the restoration benefits that might be expected following carp control. We conclude that, while further work is required (on the virus, the target species, environmental issues, and especially the identification of a suitable broad-scale complementary control measure), optimism must prevail in order to ensure an eventual solution to this important environmental problem.

Myxoma Virus-Encoded Host Range Protein M029: A Multifunctional Antagonist Targeting Multiple Host Antiviral and Innate Immune Pathways

Myxoma virus (MYXV) is the prototypic member of the Leporipoxvirus genus of the Poxviridae family of viruses. In nature, MYXV is highly restricted to leporids and causes a lethal disease called myxomatosis only in European rabbits (Oryctologous cuniculus). However, MYXV has been shown to also productively infect various types of nonrabbit transformed and cancer cells in vitro and in vivo, whereas their normal somatic cell counterparts undergo abortive infections. This selective tropism of MYXV for cancer cells outside the rabbit host has facilitated its development as an oncolytic virus for the treatment of different types of cancers. Like other poxviruses, MYXV possesses a large dsDNA genome which encodes an array of dozens of immunomodulatory proteins that are important for host and cellular tropism and modulation of host antiviral innate immune responses, some of which are rabbit-specific and others can function in nonrabbit cells as well. This review summarizes the functions of one such MYXV host range protein, M029, an ortholog of the larger superfamily of poxvirus encoded E3-like dsRNA binding proteins. M029 has been identified as a multifunctional protein involved in MYXV cellular and host tropism, antiviral responses, and pathogenicity in rabbits.

Seasonality and risk factors for myxomatosis in pet rabbits in Great Britain

Myxomatosis is a highly contagious, frequently fatal viral disease affecting both wild and domesticated European rabbits across many areas of the world. Here we used electronic health records (EHRs) collected from pet rabbits attending a sentinel voluntary network of 191 veterinary practices across Great Britain (GB) between March 2014 and June 2019 to identify new features of this disease's epidemiology. From a total of 89,408 rabbit consultations, text mining verified by domain experts identified 207 (0.23 %) cases where myxomatosis was the only differential diagnosis recorded by the attending practitioner. Cases occurred in all months but February and were distributed across the country. Consistent with studies in wild rabbits, the majority of cases occurred between August and November. However, there was also evidence for considerable variation between years. A nested case control study identified important risk factors for myxomatosis within this pet animal population including season, sex, age, vaccination status and distance to likely wild rabbit habitats. Female entire rabbits were twice as likely to be a case (odds ratio (OR) 1.98, 95 % confidence interval (CI) 1.26-3.13, p = 0.003), suggesting a novel role for behaviour in driving transmission from wild to domesticated rabbits. Vaccination had the largest protective effect with vaccinated rabbits being 8.3 times less likely to be a case than unvaccinated rabbits (OR = 0.12, 95 % CI 0.06-0.21, p = <0.001).

Oncolytic Virotherapy with Myxoma Virus

Oncolytic viruses are one of the most promising novel therapeutics for malignant cancers. They selectively infect and kill cancer cells while sparing the normal counterparts, expose cancer- specific antigens and activate the host immune system against both viral and tumor determinants. Oncolytic viruses can be used as monotherapy or combined with existing cancer therapies to become more potent. Among the many types of oncolytic viruses that have been developed thus far, members of poxviruses are the most promising candidates against diverse cancer types. This review summarizes recent advances that are made with oncolytic myxoma virus (MYXV), a member of the Leporipoxvirus genus. Unlike other oncolytic viruses, MYXV infects only rabbits in nature and causes no harm to humans or any other non-leporid animals. However, MYXV can selectively infect and kill cancer cells originating from human, mouse and other host species. This selective cancer tropism and safety profile have led to the testing of MYXV in various types of preclinical cancer models. The next stage will be successful GMP manufacturing and clinical trials that will bring MYXV from bench to bedside for the treatment of currently intractable malignancies.

Species-Specific Host-Virus Interactions: Implications for Viral Host Range and Virulence

A growing number of studies indicate that host species-specific and virus strain-specific interactions of viral molecules with the host innate immune system play a pivotal role in determining virus host range and virulence. Because interacting proteins are likely constrained in their evolution, mutations that are selected to improve virus replication in one species may, by chance, alter the ability of a viral antagonist to inhibit immune responses in hosts the virus has not yet encountered. Based on recent findings of host-species interactions of poxvirus, herpesvirus, and influenza virus proteins, we propose a model for viral fitness and host range which considers the full interactome between a specific host species and a virus, resulting from the combination of all interactions, positive and negative, that influence whether a virus can productively infect a cell and cause disease in different hosts.

The T cell receptor (TRA) locus in the rabbit (Oryctolagus cuniculus): Genomic features and consequences for invariant T cells

The rabbit has been widely used in immunology and infectiology. Rabbit immunoglobulins have been extensively studied, leading to the discovery of their idiotypes, allotypic diversity, and of the diversification of the primary repertoire by hyperconversion. Much less is known about rabbit T cell receptors (TR), especially TRA. This isotype is particularly important for innate-like T cells, which typically express invariant TRA (iTRA). The presence of such cells in the rabbit remains an enigma. Rabbit NKT cells seem to be very rare, and lagomorphs lack MAIT cells. TRAV1, the variable gene expressed in the iTRA of these cells across most mammals, and MR1, the MH1-like receptor that present riboflavin derivatives to MAIT cells, are missing in rabbit. An alternative iTRA has been identified, that may be expressed by new innate-like T cells. To facilitate TRA repertoire analyses in rabbit, we report here a full description of TRA and TRD loci and a subgroup definition based on IMGT® classification. Rabbit TRA rearrangements follow the same temporal pattern that is observed in mouse and human. Rare transcripts expressing TRDV/TRDD/TRDJ rearrangements spliced to TRAC were detected. TRA and TRD genes have been made available in IMGT and IMGT/HighV-QUEST, allowing easy analysis of TRA/TRD RepSeq.

Contrasting evolution of virulence and replication rate in an emerging bacterial pathogen

With increasing antibiotic resistance, there is a pressing need to understand how host resistance naturally influences bacterial virulence and replication rates. We test this in an infection experiment using 55 isolates of a bacterium, which were collected over the course of the epidemic following its natural emergence in a North American songbird. We demonstrate virulence has increased linearly from outbreak to the present day, encompassing >150,000 bacterial generations. Despite this, bacterial replication rate only increased during the initial spread of host resistance but not thereafter. Thus, contrary to common assumptions, virulence and replication rates can evolve independently, particularly after the initial spread of host resistance.

Host resistance through immune clearance is predicted to favor pathogens that are able to transmit faster and are hence more virulent. Increasing pathogen virulence is, in turn, typically assumed to be mediated by increasing replication rates. However, experiments designed to test how pathogen virulence and replication rates evolve in response to increasing host resistance, as well as the relationship between the two, are rare and lacking for naturally evolving host–pathogen interactions. We inoculated 55 isolates of Mycoplasma gallisepticum, collected over 20 y from outbreak, into house finches (Haemorhous mexicanus) from disease-unexposed populations, which have not evolved protective immunity to M. gallisepticum. We show using 3 different metrics of virulence (body mass loss, symptom severity, and putative mortality rate) that virulence has increased linearly over >150,000 bacterial generations since outbreak (1994 to 2015). By contrast, while replication rates increased from outbreak to the initial spread of resistance (1994 to 2004), no further increases have occurred subsequently (2007 to 2015). Finally, as a consequence, we found that any potential mediating effect of replication rate on virulence evolution was restricted to the period when host resistance was initially increasing in the population. Taken together, our results show that pathogen virulence and replication rates can evolve independently, particularly after the initial spread of host resistance. We hypothesize that the evolution of pathogen virulence can be driven primarily by processes such as immune manipulation after resistance spreads in host populations.

First outbreak of myxomatosis in Iberian hares (Lepus granatensis)

Myxomatosis is an infectious disease caused by myxoma virus (MYXV; genus Leporipoxvirus), which affects the European wild rabbit (Oryctolagus cuniculus) and sporadically brown hares (Lepus europaeus). Here, we describe the first outbreak of myxomatosis in Iberian hares (Lepus granatensis). Between mid-July and the end of September 2018, around 530 dead animals were detected in Iberian hare populations in southern Spain. The apparent mean mortality rate was 56.7%, and the estimated mean case fatality rate was 69.2%. Histopathological and molecular results confirmed MYXV infections in all hares analysed. To the authors' knowledge, this is the first myxomatosis outbreak causing a high mortality in hares and the first detailed characterization of a myxomatosis outbreak in the Iberian hare. The absence of cases in sympatric wild rabbits suggests differences in the susceptibility between both lagomorph species to the virus strain implicated in the outbreak. After the first case, the number of affected areas increased sharply affecting most of the Iberian Peninsula where the Iberian hare is present. Further studies are required to elucidate the origin of the implicated MYXV strain as well as to assess the impact of this outbreak on the Iberian hare populations.

Identification of diverse arthropod associated viruses in native Australian fleas

Fleas are important vectors of zoonotic disease. However, little is known about the natural diversity and abundance of flea viruses, particularly in the absence of disease associations, nor the evolutionary relationships among those viruses found in different parasitic vector species. Herein, we present the first virome scale study of fleas, based on the meta-transcriptomic analysis of 52 fleas collected along the eastern coast of Australia. Our analysis revealed 18 novel RNA viruses belonging to nine viral families with diverse genome organizations, although the majority (72%) possessed single-stranded positive-sense genomes. Notably, a number of the viruses identified belonged to the same phylogenetic groups as those observed in ticks sampled at the same locations, although none were likely associated with mammalian infection. Overall, we identified high levels of genomic diversity and abundance of viruses in the flea species studied, and established that fleas harbor viruses similar to those seen to other vectors.

Genetic Characterization of a Recombinant Myxoma Virus in the Iberian Hare (Lepus granatensis)

Myxomatosis is a lethal disease in wild European and domestic rabbits (Oryctolagus cuniculus), which is caused by a Myxoma virus (MYXV) infection-a leporipoxvirus that is found naturally in some Sylvilagus rabbit species in South America and California. The introduction of MYXV into feral European rabbit populations of Australia and Europe, in the early 1950s, demonstrated the best-documented field example of host-virus coevolution, following a cross-species transmission. Recently, a new cross-species jump of MYXV has been suggested in both Great Britain and Spain, where European brown hares (Lepus europaeus) and Iberian hares (Lepus granatensis) were found dead with lesions consistent with those observed in myxomatosis. To investigate the possibility of a new cross-species transmission event by MYXV, tissue samples collected from a wild Iberian hare found dead in Spain (Toledo region) were analyzed and deep sequenced. Our results reported a new MYXV isolate (MYXV Toledo) in the tissues of this species. The genome of this new virus was found to encode three disruptive genes (M009L, M036L, and M152R) and a novel ~2.8 kb recombinant region, which resulted from an insertion of four novel poxviral genes towards the 3' end of the negative strand of its genome. From the open reading frames inserted into the MYXV Toledo virus, a new orthologue of a poxvirus host range gene family member was identified, which was related to the MYXV gene M064R. Overall, we confirmed the identity of a new MYXV isolate in Iberian hares, which, we hypothesized, was able to more effectively counteract the host defenses in hares and start an infectious process in this new host.

Myxoma virus M013 protein antagonizes NF-κB and inflammasome pathways via distinct structural motifs

Among the repertoire of immunoregulatory proteins encoded by myxoma virus, M013 is a viral homologue of the viral pyrin domain-only protein (vPOP) family. In myeloid cells, M013 protein has been shown to inhibit both the inflammasome and NF-κB signaling pathways by direct binding to ASC1 and NF-κB1, respectively. In this study, a three-dimensional homology model of the M013 pyrin domain (PYD) was built based on similarities to known PYD structures. A distinctive feature of the deduced surface electrostatic map of the M013 PYD is the presence of a negatively region consisting of numerous aspartate and glutamate residues in close proximity. Single-site mutations of aspartate and glutamate residues reveal their role in interactions with ASC-1. The biological significance of charge complementarity in the M013-ASC-1 interaction was further confirmed by functional assays of caspase-1 activation and subsequent secretion of cytokines. M013 also has a unique 33-residue C-terminal tail that follows the N-terminal PYD, and it is enriched in positively charged residues. Deletion of the tail of M013 significantly inhibited the interactions between M013 and NF-κB1, thus compromising the ability of the viral protein to suppress the secretion of pro-inflammatory cytokines. These results demonstrate that vPOP M013 exploits distinct structural motifs to regulate both the inflammasome and NF-κB pathways.

The phylogenomics of evolving virus virulence

How virulence evolves after a virus jumps to a new host species is central to disease emergence. Our current understanding of virulence evolution is based on insights drawn from two perspectives that have developed largely independently: long-standing evolutionary theory based on limited real data examples that often lack a genomic basis, and experimental studies of virulence-determining mutations using cell culture or animal models. A more comprehensive understanding of virulence mutations and their evolution can be achieved by bridging the gap between these two research pathways through the phylogenomic analysis of virus genome sequence data as a guide to experimental study.

Rapid Antagonistic Coevolution in an Emerging Pathogen and Its Vertebrate Host

Host-pathogen coevolution is assumed to play a key role in eco-evolutionary processes, including epidemiological dynamics and the evolution of sexual reproduction [1-4]. Despite this, direct evidence for host-pathogen coevolution is exceptional [5-7], particularly in vertebrate hosts. Indeed, although vertebrate hosts have been shown to evolve in response to pathogens or vice versa [8-12], there is little evidence for the necessary reciprocal changes in the success of both antagonists over time [13]. Here, we generate a time-shift experiment to demonstrate adaptive, reciprocal changes in North American house finches (Haemorhous mexicanus) and their emerging bacterial pathogen, Mycoplasma gallisepticum [14-16]. Our experimental design is made possible by the existence of disease-exposed and unexposed finch populations, which were known to exhibit equivalent responses to experimental inoculation until the recent spread of genetic resistance in the former [14, 17]. Whereas inoculations with pathogen isolates from epidemic outbreak caused comparable sub-lethal eye swelling in hosts from exposed (hereafter adapted) and unexposed (hereafter ancestral) populations, inoculations with isolates sampled after the spread of resistance were threefold more likely to cause lethal symptoms in hosts from ancestral populations. Similarly, the probability that pathogens successfully established an infection in the primary host and, before inducing death, transmitted to an uninfected sentinel was highest when recent isolates were inoculated in hosts from ancestral populations and lowest when early isolates were inoculated in hosts from adapted populations. Our results demonstrate antagonistic host-pathogen coevolution, with hosts and pathogens displaying increased resistance and virulence in response to each other over time.

Sociovirology: Conflict, Cooperation, and Communication among Viruses

Viruses are involved in various interactions both within and between infected cells. Social evolution theory offers a conceptual framework for how virus-virus interactions, ranging from conflict to cooperation, have evolved. A critical examination of these interactions could expand our understanding of viruses and be exploited for epidemiological and medical interventions.