Biology subjects

Hepojoki, J.

Publications and source records attributed to Hepojoki, J..

At least 19 recordsLinked to original sources

bioRxiv2026

Histopathological and virus-associated features of Boid Inclusion Body Disease in Boa constrictor

Boid inclusion body disease (BIBD) is a reptarenavirus-induced fatal disease of boid snakes that, while diagnosed with ease due to the pathognomonic intracytoplasmic inclusion bodies (IB), is not yet fully characterized pathomorphologically and with regards to its pathogenesis. The present study retrospectively investigated a random cohort of 50 captive male and female boa constrictors of variable age (neonate to 25 years) for histopathological changes and in situ viral protein (nucleoprotein, NP, and glycoprotein 2, GP2) expression patterns. IB formation and NP expression were scored semiquantitatively. The vast majority of snakes (42/50; 84%) exhibited histopathological changes; these mainly (39/42; 93%) represented inflammatory processes that most frequently affected the gastrointestinal tract. Overall, IB and NP scores were significantly higher in the more recent cases (2020-2025) compared to the older cases (2000-2003). NP scores did not differ between age groups or sex, but were lower in animals with clinical signs and higher in those with histopathological changes. No statistically significant association was found between NP scores and inflammatory processes, neither in general nor in individual organs. GP2 expression, as an indicator of virion assembly, was less consistent than NP expression and generally restricted to individual cells with and without IBs. There was no histological evidence of overt damage in infected cells. Jointly, the results indicate different phases of restrictive and systemic viral replication that are not directly associated with pathological processes and/or clinical signs.

pathology↗

bioRxiv2026

Engineering morphology of tetrasulfide-incorporated mesoporous silica nanoparticles for enhanced mRNA delivery

Lipid nanoparticles (LNPs) are the most studied nanocarrier for mRNA delivery, yet their broader application remains limited due to suboptimal cellular uptake, low efficacy in mRNA delivery, and poor stability. In this study, we report a novel tetrasulfide-incorporated virus-like porous silica (VLPSi) nanoparticle as a safe and efficient platform to enhance LNP-mediated mRNA delivery. By systematically tuning the synthesis parameters, a series of nanoparticles with distinct morphologies and architectures were obtained, enabling the study of how tetrasulfide and particle morphology affect mRNA delivery. The performance of VLPSi was optimized by evaluating cellular uptake, cytotoxicity, and transfection performance with different lipid and mRNA payloads across multiple cell types. The results showed that increasing the length and number of spikes on the VLPSi surface significantly improved cellular uptake efficiency and subsequent mRNA expression. Mechanistically, the enhanced delivery arose from the combined effect from the nanospikes and intracellular tetrasulfide degradation. Furthermore, the nanoparticles significantly enhanced the stability of mRNA. Overall, these findings establish a structure-function relationship between virus-like topography, biodegradable silica chemistry, and mRNA delivery. This work provides a structurally tunable, biodegradable, and highly effective bioinspired nanoplatform to enhance mRNA delivery.

biochemistry↗

bioRxiv2026

A rational design strategy and validation for protease-resistant fusion-inhibitor antiviral peptides

Peptide-based fusion inhibitors are promising pharmaceuticals in the fight against enveloped viruses relying on membrane fusion for host infection. However, peptide therapeutic applications have long been hindered by their poor stability in vivo. Here, we discovered that peptide inhibitors with the wildtype sequence of the heptad repeat 2 (HR2) domain of the SARS-CoV-2 spike protein are efficiently cleaved by Transmembrane Protease, Serine 2 (TMPRSS2), a key protease involved in the SARS-CoV-2 virus-cell fusion pathway. We then identified the corresponding cleavage sites and designed three protease-resistant peptides using ranking based on deep mutational scanning and natural occurrence. The three candidates all exhibit inhibitory activity in a cell-cell fusion assay. A high-resolution cryo-EM structure of the top candidate, HR2-NHN, bound to its HR1 target reveals the molecular basis for its potent activity. The top candidate of the cell-based screening assay significantly improved efficacy relative to the wildtype peptide when administered 12 h before infection in both an authentic virus-cell infection assay and a mouse assay. More broadly, our results suggest that the design strategies for protease-resistant peptides could be applied to a broad spectrum of other enveloped viruses and pave the way for the development of safe, prophylactic antivirals that can be administered before exposure.

microbiology↗

bioRxiv2026

Bioinspired Virus-Like Porous Silica Amplify Lipid-Mediated mRNA Delivery

Lipid nanoparticles (LNPs) have demonstrated strong potential in COVID-19 mRNA vaccines nevertheless they still face the challenges in low mRNA delivery efficacy. Virus-like porous silica (VLPSi) nanoparticles (NPs) represent a promising biomimetic delivery platform because their spiked morphology may enhance cellular internalization and promote endosomal membrane disruption. However, the application of VLPSi for mRNA has been rarely explored. In this study, hybrid lipid-VLPSi NPs were developed by combining VLPSi with either lipoplexes (LPs) or LNPs. The effects of lipid types, mass ratio of different compositions, and amine modifications of VLPSi on mRNA delivery were studied. The results demonstrated that both LP and LNP could be successfully integrated with VLPSi to form hybrid delivery systems for mRNA transfection. VLPSi could significantly enhance mRNA delivery of both LPs and LNPs due to improved cellular uptake, structural stabilization of the mRNA complex, and enhanced endosomal escape mediated by the rigid virus-like surface architecture. Among the tested lipid formulations, the ionizable lipid ALC-0315 and helper lipid DOPE with mass ratio of 5:3 was the most effective lipid composition to be integrated with VLPSi, showing the highest mRNA delivery performance. In addition, amino modification of VLPSi was found to be a critical factor for efficient mRNA delivery. Hybrid LNPs containing amino-modified VLPSi showed significantly higher transfection efficiency than those containing unmodified VLPSi. Notably, amino-modified LNP-VLPSi achieved up to fivefold higher gene expression than conventional LNPs. Overall, this study establishes VLPSi as an efficient platform for amplifying lipid-mediated mRNA delivery. Owing to its straightforward integration into widely used LNP systems, VLPSi offers an adaptable and effective strategy for advancing next-generation mRNA therapeutics.

bioengineering↗

bioRxiv2026

Snake Kolmiovirus Encodes a Single Form of Delta Antigen and Shows No Evidence of Translation from Open Reading Frame 2

Hepatitis D virus (HDV) is a satellite virus that utilizes hepatitis B virus (HBV) as a helper for infectious particle formation. HDV was originally identified as a novel antigen in liver biopsies of HBV patients, and later studies showed the "delta" antigen (DAg) to be the sole protein encoded by HDV. Until the discovery of HDV-like agents in birds and snakes in 2018, HDV was a unique example of animal satellite viruses. We identified Swiss snake colony virus 1 (SwSCV-1) in the brain of a Boa constrictor, and through comparison we found the genome organization of SwSCV-1 to resemble that of HDV. However, in addition to the DAg open reading frame (ORF), the genome of SwSCV-1 includes another >500 nt ORF, "ORF2". To study whether the putative ORF2-encoded protein plays a role in the SwSCV-1 life cycle, we established an infectious clone of the virus with a point mutation in the methionine initiation codon of ORF2. The mutation did not significantly affect initiation of replication, establishment of persistent infection, or infectious particle formation upon superinfection with a helper virus. Using additional methods, we gathered further evidence confirming that ORF2 is not actively translated in boa constrictor cells. We further showed that unlike HDV, SwSCV-1 expresses a single form of the DAg. Although the proteins encoded by SwSCV-1 and HDV only include one and two forms of the DAg, respectively, whether other kolmioviruses express additional forms of DAg or related proteins in some cell types or host species merits further research. IMPORTANCEApproximately 40 years after the discovery of hepatitis D virus (HDV), satellite viruses with similar genome organization were found in various animals, thereby giving rise to family Kolmioviridae. HDV encodes a single protein, the delta antigen (DAg), which comes in small and approximately 20 amino acids longer large form. The genome of some HDV species and many of the newly found kolmioviruses contains additional open reading frames (ORFs), potentially enabling protein expression. Here, we studied the viral proteins expressed during Swiss snake colony virus 1 (SwSCV-1) infection of boa constrictor cells. Our findings show that unlike HDV, SwSCV-1 encodes only a single form of DAg. In addition, our study suggests that, like in HDV, the additional ORF in SwSCV-1 genome does not give rise to a protein. Although we could not demonstrate expression of additional viral proteins during SwSCV-1 infection, it is important to study the proteome of other kolmioviruses.

microbiology↗

bioRxiv2025

Deltaviruses spread through a viral Trojan Horse

Hepatitis D-like viral satellites, known as deltaviruses, have been recently discovered in a wide range of animals. These viruses are thought to expropriate glycoproteins from helper viruses to form infectious particles. Here, we challenge this paradigm and demonstrate that deltaviruses are packaged within helper virus particles, using them as viral Trojan Horses for cell entry. By leveraging orthogonal electronic and photonic super-resolution microscopy, we visualize deltaviruses enclosed within virions from rhabdo-, herpes-, and arenavirus families. We show that this conserved hitchhiking mechanism ensures concomitant deltavirus-helper virus spread, which advantages the dissemination of deltaviruses, broadens their host range and expands their tropism. Our findings reveal a previously unrecognized mode of viral transmission, providing a framework to investigate overlooked deltavirus infections outside of the human liver.

microbiology↗

bioRxiv2025

Mechanism of biomimetic virus-like nanoparticles in triggering immune response elucidated by proteomics

The use of biomimetic nanoparticles (NPs) with virus-like morphology have recently attracted research interest as novel delivery platforms and immune adjuvants. However, the exact interactions between the nanoparticles and immune cells as well as the mechanism involved are not known in detail. This motivated us to develop virus-like mesoporous silica nanoparticles (VLP) to characterize their physicochemical properties, and to determine the immune pathways induced by the particles in mouse macrophages. The results showed inclusion of spikes mimicking virion structures on the surface increased cellular uptake and enhanced immune response as compared to spherical NPs. Proteomic analysis revealed that the RIG-I-like receptor signaling pathway, Chemokine signaling pathway, MAPK signaling pathway, NF-{kappa}B signaling pathway, Toll-like receptor signaling pathway, B cell receptor signaling pathway and Th1 and Th2 cell differentiation pathways were involved in regulating the immune response when macrophages interacted with VLP. When the spikes increased from 5 to 30 nm, the expression levels of immune-related proteins including TRAF6 and PIAS4 proteins enhanced. This study revealed the interaction pathways and key proteins in the activation of immune response with VLP, which may provide insights to develop novel immunotherapy for enhanced efficacy. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=177 SRC="FIGDIR/small/640536v3_ufig1.gif" ALT="Figure 1"> View larger version (43K): org.highwire.dtl.DTLVardef@395d6forg.highwire.dtl.DTLVardef@25238dorg.highwire.dtl.DTLVardef@41001borg.highwire.dtl.DTLVardef@16dfe2e_HPS_FORMAT_FIGEXP M_FIG C_FIG

immunology↗

bioRxiv2024

Multifocal cutaneous neoplastic vascular proliferations in a rainbow boa (Epicrates cenchria) collection with boid inclusion body disease

Reports on neoplastic processes in snakes are sparse regardless of their location, origin or behavior. Here, we describe the occurrence of multifocal cutaneous neoplastic processes consistent with hemangioma and hemangioendothelioma, with a differential diagnosis of angiomatosis, in a colony of native Brazilian rainbow boas (Epicrates cenchria) which also included animals affected by boid inclusion body disease (BIBD). Thirteen snakes were affected; seven of these had been introduced from other Brazilian sites years earlier, the others had been bred in house but were not offspring of knowingly affected animals. The breeding regime allowed contact between all female and male animals over the years. The cutaneous lesions were first observed over eight years ago, with additional cases detected during the three following years, but no new cases in the last five years. Two affected animals were subjected to a post mortem examination and were found to suffer from peliosis hepatis as one of the additional pathological changes. BIBD was confirmed in five of the eight examined animals, by histology, immunohistology for reptarenavirus nucleoprotein, and multiplex RT-PCR targeting the reptarenavirus S segment. Reptarenavirus infection was also detected in cells in the cutaneous neoplastic processes. PCRs for Bartonella henselae and B. quintana as well as bacterial DNA in general, performed on a pool of six skin lesions, yielded negative results, ruling out ongoing bacterial infection, like bacillary angiomatosis in humans, of the lesions. The results hint towards an association of reptarenavirus infection and BIBD with neoplastic processes which is worth further investigations.

pathology↗

bioRxiv2024

Circulating mucosal-like IgA responses associate with severity of Puumala orthohantavirus-caused hemorrhagic fever with renal syndrome

Old World Orthohantaviruses cause hemorhagic fever with renal syndrome (HFRS) characterized by increased vascular permeability and acute kidney injury (AKI). Despite the systemic nature of the disease, the virus enters humans through inhalation and therefore initially encounters the immunoglobulin class A (IgA) dominated mucosal immune system. Herein, we characterized systemic IgA responses and their potential relationship to the mucosal immune activation by examining blood samples obtained from patients hospitalized due to acute Puumala orthohantavirus infection. Our findings reveal increased frequencies of IgA-expressing circulating mucosal-associated B1 cells and plasmablasts, as well as elevated levels of polyreactive, polymeric, virus-specific and secretory IgA in the acute stage of the disease. Importantly, the levels of circulating virus-specific and secretory IgA associated with the severity of AKI. Furthermore, circulating polymeric IgA displayed enhanced effector functions by forming stable complexes with the IgA receptor CD89 and induced pro-inflammatory neutrophil responses. These results suggest that, while an efficient mucosal immune response is likely to be crucial for infection clearance, an excessive mucosal immune activation may contribute to HFRS disease progression.

immunology↗

bioRxiv2023

Unraveling human, rodent and snake Kolmioviridae replication to anticipate cross-species transmission

The recent discovery of Hepatitis D (HDV)-like viruses across a wide range of taxa led to the establishment of the Kolmioviridae family. Recent studies suggest that kolmiovirids can be satellites of viruses other than Hepatitis B virus (HBV), challenging the strict HBV/HDV-association dogma. Studying whether kolmiovirids are able to replicate in any animal cell they enter is essential to assess their zoonotic potential. Here, we compared replication of three kolmiovirids: HDV, rodent (RDeV) and snake deltavirus (SDeV) in vitro and in vivo. We show that SDeV has the narrowest and RDeV the broadest host cell range. High resolution imaging of infected cells revealed nuclear viral hubs with a peculiar RNA-protein organization. Finally, in vivo hydrodynamic delivery of infectious clones showed that both HDV and RDeV, but not SDeV, efficiently replicate in mouse liver, forming massive nuclear viral hubs. Our comparative analysis lays the foundation for the discovery of specific host factors controlling Kolmioviridae host-shifting.

microbiology↗

bioRxiv2022

Reptarenavirus Co- and Superinfection in Cell Culture Sheds Light on the S and L Segment Accumulation in Captive Snakes

Boid inclusion body disease (BIBD) caused by reptarenaviruses affects collections of captive constrictor snakes worldwide. The disease manifests by formation of cytoplasmic inclusion bodies (IBs) in various tissues. Curiously, a snake with BIBD most often carries more than a single pair of genetically distinct reptarenavirus S and L segments, and the tissues of an infected individual can show variation in the variety of different S and L segment species. The role of reptarenavirus coinfection in development of BIBD remains unknown, and it is unclear how the infection affects the susceptibility to reptarenavirus superinfection or to secondary infection by other agents. Because cell culture studies with mammarenaviruses have demonstrated persistently infected cultures to resist superinfection by genetically similar viruses, we hypothesized that coinfection would only occur if the infecting viruses were of two different species. To study the hypothesis, we employed boa constrictor kidney- and brain-derived cell cultures to perform a set of co- and superinfection experiments with five reptarenavirus and one hartmanivirus isolates. Analysis of viral RNA released from coinfected cells using qRT-PCR did not demonstrate evident competition between reptarenaviruses of the same or different species in the boa constrictor kidney-derived cell line. The experiments on the brain-derived cell line revealed considerable differences in the replication ability of the reptarenaviruses tested, suggesting varying tissue specificity or target cell spectra for reptarenavirus species. Finally, experiments on persistently reptarenavirus infected cell lines showed reduced replication of closely related reptarenaviruses while the replication of reptarenaviruses from different species appeared unaffected. IMPORTANCESnakes with boid inclusion body disease (BIBD) often display reptarenavirus coinfections, or presence of unbalanced S and L segment ratios. Studies on mammarenaviruses suggest replication interference between closely but not between more distantly related viruses. In the study, we provide evidence that similar interference or competition between segments occurs also in the case of reptarenaviruses. Conversely, the results show that there is very little or no competition between more distantly related L or S segments, the cells release similar amounts of viral RNA segments in the case of mono and coinfection. Successful superinfections of persistently infected cell cultures suggest that the unbalanced S and L segment pools often seen in the infected animals could be a result of segment accumulation through sequential reptarenavirus co- and superinfections during breeding in captivity.

microbiology↗

bioRxiv2022

Boid Inclusion Body Disease (BIBD) Is Also a Disease of Wild Boa Constrictors

Reptarenaviruses cause Boid Inclusion Body Disease (BIBD), a potentially fatal disease, occurring in captive constrictor snakes boas and pythons worldwide. Classical BIBD, characterized by the formation of pathognomonic cytoplasmic inclusion bodies (IBs), occurs mainly in boas, whereas in pythons, for example, reptarenavirus infection most often manifests as central nervous system signs with limited IB formation. The natural hosts of reptarenaviruses are unknown, although wild constrictor snakes are among the suspects. Here, we report BIBD with reptarenavirus infection in indigenous captive and wild boid snakes in Costa Rica using histology, immunohistology, transmission electron microscopy, next-generation sequencing (NGS), and RT-PCR. The snakes studied represented diagnostic post mortem cases of captive and wild caught snakes since 1989. The results from NGS on archival paraffin blocks confirm that reptarenaviruses have been present in wild boa constrictors in Costa Rica already in the 1980s. Continuous sequences de novo assembled from the low-quality RNA obtained from paraffin embedded tissue allowed the identification of a distinct pair of reptrarenavirus S and L segments in all studied animals; in most cases reference assembly could recover almost complete segments. Sampling of three prospective cases in 2018 allowed examination of fresh blood or tissues, and resulted in identification of additional reptarenavirus segments and hartmanivirus co-infection. Our results show that BIBD is not only a disease of captive snakes, but also occurs in indigenous wild constrictor snakes in Costa Rica, suggesting boa constrictors to play a role in natural reptarenavirus circulation. IMPORTANCEThe literature describes cases of boid inclusion body disease (BIBD) in captive snakes since the 1970s, and in the 2010s, others and we identified reptarenaviruses as the causative agent. BIBD affects captive snakes globally, but the origin and the natural host of reptarenaviruses remains unknown. In this report, we show BIBD and reptarenavirus infections in two native Costa Rican constrictor snake species, and by studying archival samples, we show that both the viruses and the disease have been present in wild snakes in Costa Rica at least since the 1980s. The diagnosis of BIBD in wild boa constrictors suggests that this species plays a role in the circulation of reptarenaviruses. Additional sample collection and analysis would help to clarify this role further and the possibility of e.g. vector transmission from an arthropod host.

microbiology↗

bioRxiv2021

Intranasal inhibitor blocks Omicron and other variants of SARS-CoV-2

The recent emergence of novel SARS-CoV-2 variants capable of efficiently escaping neutralizing antibodies emphasizes the need for prophylactic strategies to complement vaccination in fighting the COVID-19 pandemic. Nasal epithelium is rich in the ACE2 receptor and important for SARS-CoV-2 transmission by supporting early viral replication before seeding to the lung1. Intranasal administration of SARS-CoV-2 neutralizing antibodies or antibody fragments has shown encouraging potential as a protective measure in animal models2-5. However, there remains a dire need for SARS-CoV-2 blocking agents that are less vulnerable to mutational variation in the neutralization epitopes of the viral spike glycoprotein and more economical to produce in large scale. Here we describe TriSb92, a highly manufacturable and extremely stable trimeric human SH3 domain-derived antibody mimetic targeted against a conserved region in the receptor-binding domain of spike. TriSb92 potently neutralizes SARS-CoV-2 and its variants of concern, including Omicron BA.5 as well as the latest and most immunoevasive variants like BF.7, XBB, and BQ.1.1. Intranasal administration of a modest dose of TriSb92 (5 or 50 micrograms) as early as eight hours before a challenge with SARS-CoV-2 efficiently protected mice from infection, and was still effective even when given 4 h after the viral challenge. The target epitope of TriSb92 was defined by cryo-EM, which revealed triggering of a conformational shift in the spike trimer rather than competition for ACE2 binding as the molecular basis of its strong inhibitory action. The high potency and robust biochemical properties of TriSb92 together with the remarkable resistance of its inhibitory action against viral sequence evolution suggest that TriSb92 could be useful as a nasal spray for protecting susceptible individuals from SARS-CoV-2 infection.

microbiology↗

bioRxiv2021

Short '1.2x genome' infectious clone initiates deltavirus replication in Boa constrictor cells

Human hepatitis D virus (HDV), discovered in 1977, represented the sole known deltavirus for decades. The dependence on hepatitis B virus (HBV) co-infection and its glycoproteins for infectious particle formation led to the assumption that deltaviruses are human-only pathogens. However, since 2018, several reports have described identification of HDV-like agents from various hosts but without co-infecting hepadnaviruses. Indeed, we demonstrated that Swiss snake colony virus 1 (SwSCV-1) uses arenaviruses as the helper for infectious particle formation, thus shaking the dogmatic alliance with hepadnaviruses for completing deltavirus life cycle. In vitro systems enabling helper virus-independent replication are key for studying the newly discovered deltaviruses. Others and we have successfully used constructs containing multimers of the deltavirus genome for the replication of various deltaviruses via transfection in cell culture. Here, we report the establishment of deltavirus infectious clones with 1.2x genome inserts bearing two copies of the genomic and antigenomic ribozymes. We used SwSCV-1 as the model to compare the ability of the previously reported "2x genome" and the "1.2x genome" plasmid constructs/infectious clones to initiate replication in cell culture. Using immunofluorescence, qRT-PCR, immuno- and northern blotting, we found the 2x and 1.2x genome clones to similarly initiate deltavirus replication in vitro and both induced a persistent infection of snake cells. We hypothesize that duplicating the ribozymes facilitates the cleavage of genome multimers into unit-length pieces during the initial round of replication. The 1.2x genome constructs enable easier introduction of modifications required for studying deltavirus replication and cellular interactions. IMPORTANCEHepatitis D virus (HDV) is a satellite virus infecting humans with strict association to hepatitis B virus (HBV) co-infection because HBV glycoproteins can mediate infectious HDV particle formation. For decades, HDV was the sole representative of deltaviruses, which had led to hypotheses suggesting that it evolved in humans, the only known natural host. Recent sequencing studies have led to the discovery of HDV-like sequences across a wide range of species, representing a paradigm shift in deltavirus evolution. Molecular biology tools such as infectious clones, which enable initiation of deltavirus infection without helper virus, are key to demonstrate that the recently found deltaviruses are capable of independent replication. Such tools will enable identification of the potential helper viruses. Here, we report a 1.2x genome copy strategy for designing plasmid-based infectious clones to study deltaviruses and to demonstrate that plasmid delivery into cultured snake cells sufficiently initiates replication of different deltaviruses.

molecular biology↗

bioRxiv2020

Experimental Reptarenavirus Infection of Boa constrictor and Python regius

Boid inclusion body disease (BIBD) causes losses in captive constrictor snake populations globally. BIBD associates with formation of cytoplasmic inclusion bodies (IB) which mainly comprise reptarenavirus nucleoprotein (NP). In 2017, BIBD was reproduced by cardiac injection of boas and pythons with reptarenaviruses, thus demonstrating a causative link between reptarenavirus infection and the disease. Herein, we report experimental infections of pythons (N=16) and boas (N=16) with three reptarenavirus isolates. First, we used pythons (N=8) to test two virus delivery routes: intraperitoneal injection and tracheal instillation. Independent of the delivery route, we detected viral RNA but no IBs in tissues two weeks post inoculation. Next, we inoculated pythons (N=8) via the trachea. During the four month following the infection snakes showed transient central nervous system (CNS) signs but lacked detectable IB at the time of euthanasia. One of the snakes developed severe CNS signs and we succeeded in re-isolating the virus from the brain of this individual, and could demonstrate viral antigen in neurons. In a third attempt, we tested co-housing, vaccination, and sequential infection with multiple reptarenavirus isolates on boas (N=16). At 10 months post inoculation all except one snake tested positive for viral RNA but none exhibited the characteristic IB. Analysis of the antibody responses demonstrated lower neutralizing but higher anti-reptarenavirus NP titers in experimentally versus naturally reptarenavirus infected boas. Our findings suggest that in addition to reptarenavirus infection, other factors, e.g. the antibody response, contribute to BIBD pathogenesis. IMPORTANCEA 2017 study demonstrated cardiac reptarenavirus injection to induce boid inclusion body disease (BIBD) in pythons and boas. In the present study, we experimentally infected pythons and boas with reptarenavirus via either intraperitoneal injection or tracheal instillation. We found both virus delivery routes to result in infection; though the latter could reflect the natural route of infection. In the experimentally infected snakes, we did not find evidence of inclusion body (IB) formation, characteristic to BIBD, in pythons or in boas. Most of the snakes (11/12) studied were reptarenavirus infected after ten-month follow up, which suggests that they could eventually have developed BIBD. We further found differences between the antibody responses of experimentally and naturally reptarenavirus infected snakes, which could indicate that the pathogenesis of BIBD involves factors additional to reptarenavirus infection. As snakes are poikilotherm, also the housing conditions could have an effect.

microbiology↗

bioRxiv2020

Neuropilin-1 facilitates SARS-CoV-2 cell entry and provides a possible pathway into the central nervous system

The causative agent of the current pandemic and coronavirus disease 2019 (COVID-19) is the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)1. Understanding how SARS-CoV-2 enters and spreads within human organs is crucial for developing strategies to prevent viral dissemination. For many viruses, tissue tropism is determined by the availability of virus receptors on the surface of host cells2. Both SARS-CoV and SARS-CoV-2 use angiotensin-converting enzyme 2 (ACE2) as a host receptor, yet, their tropisms differ3-5. Here, we found that the cellular receptor neuropilin-1 (NRP1), known to bind furin-cleaved substrates, significantly potentiates SARS-CoV-2 infectivity, which was inhibited by a monoclonal blocking antibody against the extracellular b1b2 domain of NRP1. NRP1 is abundantly expressed in the respiratory and olfactory epithelium, with highest expression in endothelial cells and in the epithelial cells facing the nasal cavity. Neuropathological analysis of human COVID-19 autopsies revealed SARS-CoV-2 infected NRP1-positive cells in the olfactory epithelium and bulb. In the olfactory bulb infection was detected particularly within NRP1-positive endothelial cells of small capillaries and medium-sized vessels. Studies in mice demonstrated, after intranasal application, NRP1-mediated transport of virus-sized particles into the central nervous system. Thus, NRP1 could explain the enhanced tropism and spreading of SARS-CoV-2.

microbiology↗

bioRxiv2020

Molecular rationale for hantavirus neutralization by a reservoir host-derived monoclonal antibody

The intricate lattice of Gn and Gc glycoprotein spike complexes at the surface of hantaviruses facilitates host-cell entry and is the primary target of the neutralizing antibody-mediated immune response. Here, through study of a neutralizing monoclonal antibody (mAb 4G2) generated in a bank vole reservoir host following infection with Puumala virus (PUUV), we provide molecular-level insights into how antibody-mediated targeting of the hantaviral glycoprotein lattice effectively neutralizes the virus. Crystallographic analysis reveals that mAb 4G2 binds to a multi-domain site on Gc in the pre-fusion state, and that Fab binding is incompatible with the conformational changes of the Gc that are required for host cell entry. Cryo-electron microscopy of PUUV-like particles treated with Fab 4G2 demonstrates that the antibody binds to monomeric Gc at breaks in the Gn-Gc lattice, highlighting the immunological accessibility of Gc monomers on the mature hantavirus surface and the plastic nature of the higher-order lattice assembly. This work provides a structure-based blueprint for rationalizing antibody-mediated targeting of hantaviruses.

microbiology↗

bioRxiv2020

Python nidoviruses, more than respiratory pathogens

In recent years nidoviruses have emerged as an important respiratory pathogen of reptiles, affecting especially captive python populations. In pythons, nidovirus infection induces an inflammation of the upper respiratory and alimentary tract which can develop into a severe and often fatal proliferative pneumonia. We observed pyogranulomatous and fibrinonecrotic lesions in organ systems other than the respiratory tract during full post mortem examinations on 30 nidovirus RT-PCR positive pythons of varying species originating from Switzerland and Spain. The observations prompted us to study whether the atypical tissue tropism associates with previously unknown nidoviruses or changes in the nidovirus genome. RT-PCR and inoculation of Morelia viridis cell cultures served to recruit the cases and to obtain virus isolates. Immunohistochemistry and immunofluorescence staining against nidovirus nucleoprotein demonstrated that the virus not only infects a broad spectrum of epithelial (respiratory and alimentary epithelium, hepatocytes, renal tubules, pancreatic ducts etc.), but also intravascular monocytes, intralesional macrophages and endothelial cells. By next-generation sequencing we obtained full length genome for a novel nidovirus species circulating in Switzerland. Analysis of viral genomes recovered from pythons showing nidovirus infection-associated respiratory or systemic disease did not explain the observed phenotypes. The results indicate that python nidoviruses have a broad cell and tissue tropism, further suggesting that the course of infection could vary and involve lesions in a broad spectrum of tissues and organ systems as a consequence of monocyte-mediated systemic spread of the virus. IMPORTANCEDuring the last years, python nidoviruses have become a primary cause of fatal disease in pythons. Nidoviruses represent a threat to captive snake collections, as they spread rapidly and can be associated with high morbidity and mortality. Our study indicates that, different from previously evidence, the viruses do not only affect the respiratory tract, but can spread in the entire body with blood monocytes, have a broad spectrum of target cells, and can induce a variety of lesions. Nidovirales is an order of animal and human viruses that compromise important zoonotic pathogens such as MERS-CoV and SARS-CoV, as well as the recently emerged SARS-CoV-2. Python nidoviruses belong to the same subfamily as the mentioned human viruses and show similar characteristics (rapid spread, respiratory and gastrointestinal tropism, etc.). The present study confirms the relevance of natural animal diseases to better understand the complexity of viruses of the order nidovirales.

pathology↗