Publications by authors named "Martin Beer"

504 Publications

Antigenic and Molecular Characterization of Virulent Newcastle Disease Viruses Circulating in Ethiopia Between 1976 and 2008.

Vet Med (Auckl) 2021 4;12:129-140. Epub 2021 Jun 4.

Institute of Infectology, Friedrich-Loeffler-Institut, Greifswald, Germany.

Introduction: Newcastle disease virus (NDV) cultures held in the isolate collections in Ethiopia between 1976 and 2008 were not characterized using biological and molecular techniques. The already characterized NDV isolates belonged to genotype VI but the genetic nature of previously collected isolates, which could shade light on the history of introduction into the country and their evolutionary relationships, were not established.

Methods: A total of 14 NDVs (11 obtained from outbreak cases in chickens and three commercial vaccinal strains used in the country) were inoculated into specific pathogen free (SPF) embryonated chicken eggs (ECE). Allantoic fluids harvested from grown SPF ECE were tested by heamagglutination (HA) and heamagglutination inhibition (HI) tests. Partial F gene sequences were generated for all samples and molecular evolutionary relationships were reconstructed together with reference sequences freely available online. The pathogenicities of the isolates were assessed in vivo by determining their intracerebral pathogenicity index (ICPI) in day-old chicks and molecularly by determination of F gene cleavage sites.

Results: Of these, 12 viruses (two vaccines and 10 outbreaks) were successfully propagated as evidenced by a positive heamagglutination (HA) test. These 12 propagated viruses were further characterized by heamagglutination inhibition (HI) test, of which only three viruses reacted with monoclonal antibody (MAb 617/616) specific for pigeon paramyxovirus-1. In addition, all 14 viruses were characterized by partial fusion (F) gene sequencing and phylogenetic tree reconstruction. The Ethiopian NDV isolates clustered with genotype VI viruses, forming two clades (groups 1 and 2) that have ancestral relationships with Egypt-1990 and Sudan-1975 like viruses.

Discussion: The characterized genotype VI NDVs were genetically similar to currently circulating NDVs in Ethiopia. The isolates had cleavage sites consistent with mesogenic/velogenic NDV with a mean ICPI value of 1.76, indicating that the isolates were velogenic. Two and four highly virulent viruses were thermostable at 56°C for 2 hours and 1 hour, respectively. To reduce chicken mortality and production losses, proper control of the disease should be instituted using high quality and protective vaccines together with strong biosecurity measures.
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http://dx.doi.org/10.2147/VMRR.S297281DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8187085PMC
June 2021

Adherent and suspension baby hamster kidney cells have a different cytoskeleton and surface receptor repertoire.

PLoS One 2021 4;16(6):e0246610. Epub 2021 Jun 4.

Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, Greifswald, Insel Riems, Germany.

Animal cell culture, with single cells growing in suspension, ideally in a chemically defined environment, is a mainstay of biopharmaceutical production. The synthetic environment lacks exogenous growth factors and usually requires a time-consuming adaptation process to select cell clones that proliferate in suspension to high cell numbers. The molecular mechanisms that facilitate the adaptation and that take place inside the cell are largely unknown. Especially for cell lines that are used for virus antigen production such as baby hamster kidney (BHK) cells, the restriction of virus growth through the evolution of undesired cell characteristics is highly unwanted. The comparison between adherently growing BHK cells and suspension cells with different susceptibility to foot-and-mouth disease virus revealed differences in the expression of cellular receptors such as integrins and heparan sulfates, and in the organization of the actin cytoskeleton. Transcriptome analyses and growth kinetics demonstrated the diversity of BHK cell lines and confirmed the importance of well-characterized parental cell clones and mindful screening to make sure that essential cellular features do not get lost during adaptation.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0246610PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8177424PMC
June 2021

The Second Wave of SARS-CoV-2 Circulation-Antibody Detection in the Domestic Cat Population in Germany.

Viruses 2021 05 27;13(6). Epub 2021 May 27.

Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, Südufer 10, 17493 Greifswald-Insel Riems, Germany.

Registered cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections in the German human population increased rapidly during the second wave of the SARS-CoV-2 pandemic in winter 2020/21. Since domestic cats are susceptible to SARS-CoV-2, the occurrence of trans-species transmission needs to be monitored. A previous serosurvey during the first wave of the pandemic detected antibodies against SARS-CoV-2 in 0.65% of feline serum samples that were randomly sampled across Germany. In the here-presented follow-up study that was conducted from September 2020 to February 2021, the seroprevalence rose to 1.36% (16/1173). This doubling of the seroprevalence in cats is in line with the rise of reported cases in the human population and indicates a continuous occurrence of trans-species transmission from infected owners to their cats.
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http://dx.doi.org/10.3390/v13061009DOI Listing
May 2021

A Semiquantitative Scoring System for Histopathological and Immunohistochemical Assessment of Lesions and Tissue Tropism in Avian Influenza.

Viruses 2021 05 9;13(5). Epub 2021 May 9.

Institute of Veterinary Pathology, Leipzig University, 04103 Leipzig, Germany.

The main findings of the post-mortem examination of poultry infected with highly pathogenic avian influenza viruses (HPAIV) include necrotizing inflammation and viral antigen in multiple organs. The lesion profile displays marked variability, depending on viral subtype, strain, and host species. Therefore, in this study, a semiquantitative scoring system was developed to compare histopathological findings across a wide range of study conditions. Briefly, the severity of necrotizing lesions in brain, heart, lung, liver, kidney, pancreas, and/or lymphocytic depletion in the spleen is scored on an ordinal four-step scale (0 = unchanged, 1 = mild, 2 = moderate, 3 = severe), and the distribution of the viral antigen in parenchymal and endothelial cells is evaluated on a four-step scale (0 = none, 1 = focal, 2 = multifocal, 3 = diffuse). These scores are used for a meta-analysis of experimental infections with H7N7 and H5N8 (clade 2.3.4.4b) HPAIV in chickens, turkeys, and ducks. The meta-analysis highlights the rather unique endotheliotropism of these HPAIV in chickens and a more severe necrotizing encephalitis in H7N7-HPAIV-infected turkeys. In conclusion, the proposed scoring system can be used to condensate HPAIV-typical pathohistological findings into semiquantitative data, thus enabling systematic phenotyping of virus strains and their tissue tropism.
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http://dx.doi.org/10.3390/v13050868DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8151536PMC
May 2021

Genetic and antigenic evolution of H1 swine influenza A viruses isolated in Belgium and the Netherlands from 2014 through 2019.

Sci Rep 2021 May 28;11(1):11276. Epub 2021 May 28.

Laboratory of Virology, Department of Virology, Parasitology and Immunology, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820, Merelbeke, Belgium.

Surveillance of swine influenza A viruses (swIAV) allows timely detection and identification of new variants with potential zoonotic risks. In this study, we aimed to identify swIAV subtypes that circulated in pigs in Belgium and the Netherlands between 2014 and 2019, and characterize their genetic and antigenic evolution. We subtyped all isolates and analyzed hemagglutinin sequences and hemagglutination inhibition assay data for H1 swIAV, which were the dominant HA subtype. We also analyzed whole genome sequences (WGS) of selected isolates. Out of 200 samples, 89 tested positive for swIAV. swIAV of H1N1, H1N2 and H3N2 subtypes were detected. Analysis of WGS of 18 H1 swIAV isolates revealed three newly emerged genotypes. The European avian-like H1 swIAV (lineage 1C) were predominant and accounted for 47.2% of the total isolates. They were shown to evolve faster than the European human-like H1 (1B lineage) swIAV, which represented 27% of the isolates. The 2009 pandemic H1 swIAV (lineage 1A) accounted for only 5.6% of the isolates and showed divergence from their precursor virus. These results point to the increasing divergence of swIAV and stress the need for continuous surveillance of swIAV.
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http://dx.doi.org/10.1038/s41598-021-90512-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8163766PMC
May 2021

Comparison of genomic and antigenic properties of Newcastle Disease virus genotypes II, XXI and VII from Egypt do not point to antigenic drift as selection marker.

Transbound Emerg Dis 2021 May 6. Epub 2021 May 6.

Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, Institute of Diagnostic Virology, 17493, Greifswald Insel-Riems, Germany.

Newcastle disease (ND), caused by avian orthoavulavirus type-1 (NDV), is endemic in poultry in many regions of the world and causes continuing outbreaks in poultry populations. In the Middle East, genotype XXI, , used to be present in poultry in Egypt but has been replaced by genotype VII. We investigated whether virus evolution contributed to superseding and focused on the antigenic sites within the Hemagglutinin-Neuraminidase (HN) spike protein. Full length sequences of an NDV genotype VII isolate currently circulating in Egypt was compared to a genotype XXI isolate that was present as co-infection with vaccine type viruses (II) in a historical virus isolated in 2011. Amino acid differences in the HN glycoprotein for both XXI and VII viruses amounted to 11.7% and 11.9 %, respectively, compared to the La Sota vaccine type. However, mutations within the globular head (aa 126-570), bearing relevant antigenic sites, were underrepresented (aa divergence of 8.8% and 8.1 % compared to 22.4% and 25.6% within the protein domains encompassing cytoplasmic tail, transmembrane part and stalk regions (aa 1-125) for genotypes XXI and VII, respectively). Nevertheless, reaction patterns of HN-specific monoclonal antibodies inhibiting receptor binding revealed differences between vaccine type viruses and genotype XXI and VII viruses for epitopes located in the head domain. Accordingly, compared to Egyptian vaccine type isolates and the La Sota vaccine reference strain, single aa substitutions in 6 of 10 described neutralizing epitopes of HN were found. However, the same alterations in neutralization sensitive epitopes were present in old genotype XXI as well as in newly emerged genotype VII isolates. In addition, isolates were indistinguishable by polyclonal chicken sera raised against different genotypes including vaccine viruses. These findings suggest that factors other than antigenic differences within the HN protein account for facilitating the spread of genotype VII versus genotype XXI viruses in Egypt.
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http://dx.doi.org/10.1111/tbed.14121DOI Listing
May 2021

Egyptian Fruit Bats () Were Resistant to Experimental Inoculation with Avian-Origin Influenza A Virus of Subtype H9N2, But Are Susceptible to Experimental Infection with Bat-Borne H9N2 Virus.

Viruses 2021 04 14;13(4). Epub 2021 Apr 14.

Institute of Novel and Emerging Infectious Diseases, Friedrich-Loeffler-Institut, Insel Riems, 17493 Greifswald, Insel Riems, Germany.

Influenza A viruses (IAV) of subtype H9N2, endemic in world-wide poultry holdings, are reported to cause spill-over infections to pigs and humans and have also contributed substantially to recent reassortment-derived pre-pandemic zoonotic viruses of concern, such as the Asian H7N9 viruses. Recently, a H9N2 bat influenza A virus was found in Egyptian fruit bats (), raising the question of whether this bat species is a suitable host for IAV. Here, we studied the susceptibility, pathogenesis and transmission of avian and bat-related H9N2 viruses in this new host. In a first experiment, we oronasally inoculated six Egyptian fruit bats with an avian-related H9N2 virus (A/layer chicken/Bangladesh/VP02-plaque/2016 (H9N2)). In a second experiment, six Egyptian fruit bats were inoculated with the newly discovered bat-related H9N2 virus (A/bat/Egypt/381OP/2017 (H9N2)). While turned out to be refractory to an infection with H9N2 avian-type, inoculation with the bat H9N2 subtype established a productive infection in all inoculated animals with a detectable seroconversion at day 21 post-infection. In conclusion, Egyptian fruit bats are most likely not susceptible to the avian H9N2 subtype, but can be infected with fruit bat-derived H9N2. H9-specific sero-reactivities in fruit bats in the field are therefore more likely the result of contact with a bat-adapted H9N2 strain.
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http://dx.doi.org/10.3390/v13040672DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8070959PMC
April 2021

Putative Novel Atypical BTV Serotype '36' Identified in Small Ruminants in Switzerland.

Viruses 2021 04 21;13(5). Epub 2021 Apr 21.

Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, Südufer 10, 17493 Greifswald-Insel Riems, Germany.

We identified a putative novel atypical BTV serotype '36' in Swiss goat flocks. In the initial flock clinical signs consisting of multifocal purulent dermatitis, facial oedema and fever were observed. Following BTV detection by RT-qPCR, serotyping identified BTV-25 and also a putative novel BTV serotype in several of the affected goats. We successfully propagated the so-called "BTV-36-CH2019" strain in cell culture, developed a specific RT-qPCR targeting Segment 2, and generated the full genome by high-throughput sequencing. Furthermore, we experimentally infected goats with BTV-36-CH2019. Regularly, EDTA blood, serum and diverse swab samples were collected. Throughout the experiment, neither fever nor clinical disease was observed in any of the inoculated goats. Four goats developed BTV viremia, whereas one inoculated goat and the two contact animals remained negative. No viral RNA was detected in the swab samples collected from nose, mouth, eye, and rectum, and thus the experimental infection of goats using this novel BTV serotype delivered no indications for any clinical symptoms or vector-free virus transmission pathways. The subclinical infection of the four goats is in accordance with the reports for other atypical BTVs. However, the clinical signs of the initial goat flock did most likely not result from infection with the novel BTV-36-CH0219.
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http://dx.doi.org/10.3390/v13050721DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8143309PMC
April 2021

Probe-Based Real-Time qPCR Assays for a Reliable Differentiation of Capripox Virus Species.

Microorganisms 2021 Apr 6;9(4). Epub 2021 Apr 6.

Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, Südufer 10, D-17493 Greifswald-Insel Riems, Germany.

Outbreaks of the three capripox virus species, namely lumpy skin disease virus, sheeppox virus, and goatpox virus, severely affect animal health and both national and international economies. Therefore, the World Organization for Animal Health (OIE) classified them as notifiable diseases. Until now, discrimination of capripox virus species was possible by using different conventional PCR protocols. However, more sophisticated probe-based real-time qPCR systems addressing this issue are, to our knowledge, still missing. In the present study, we developed several duplex qPCR assays consisting of different types of fluorescence-labelled probes that are highly sensitive and show a high analytical specificity. Finally, our assays were combined with already published diagnostic methods to a diagnostic workflow that enables time-saving, reliable, and robust detection, differentiation, and characterization of capripox virus isolates.
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http://dx.doi.org/10.3390/microorganisms9040765DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8067474PMC
April 2021

Full-Genome Sequences and Phylogenetic Analysis of Archived Danish European Bat Lyssavirus 1 (EBLV-1) Emphasize a Higher Genetic Resolution and Spatial Segregation for Sublineage 1a.

Viruses 2021 04 7;13(4). Epub 2021 Apr 7.

Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut (FLI), WHO Collaborating Centre for Rabies Surveillance and Research, OIE Reference Laboratory for Rabies, 17493 Greifswald-Insel Riems, Germany.

European bat lyssavirus type 1 (EBLV-1) is the causative agent for almost all reported rabies cases found in European bats. In recent years, increasing numbers of available EBLV-1 full genomes and their phylogenetic analyses helped to further elucidate the distribution and genetic characteristics of EBLV-1 and its two subtypes, namely EBLV-1a and EBLV-1b. Nonetheless, the absence of full-genome sequences from regions with known detections of EBLV-1 still limit the understanding of the phylogeographic relations between viruses from different European regions. In this study, a set of 21 archived Danish EBLV-1 samples from the years 1985 to 2009 was processed for the acquisition of full-genome sequences using a high-throughput sequencing approach. Subsequent phylogenetic analysis encompassing all available EBLV-1 full genomes from databases revealed the Danish sequences belong to the EBLV-1a subtype and further highlighted the distinct, close phylogenetic relationship of Danish, Dutch and German isolates in this region. In addition, the formation of five putative groups nearly exclusively formed by Danish isolates and the overall increased resolution of the EBLV-1a branch indicate a higher genetic diversity and spatial segregation for this sublineage than was previously known. These results emphasize the importance of phylogenetic analyses of full-genome sequences of lyssaviruses for genetic geography.
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http://dx.doi.org/10.3390/v13040634DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8067844PMC
April 2021

Monoclonal antibodies specific for the hemagglutinin-neuraminidase protein define neutralizing epitopes specific for Newcastle disease virus genotype 2.VII from Egypt.

Virol J 2021 Apr 26;18(1):86. Epub 2021 Apr 26.

Institute for Diagnostic Virology, Friedrich-Loeffler-Institute, Südufer 10, 17493, Greifswald-Insel Riems, Germany.

Background: Newcastle disease is a devastating disease in poultry caused by virulent Newcastle disease virus (NDV), a paramyxovirus endemic in many regions of the world despite intensive vaccination. Phylogenetic analyses reveal ongoing evolution of the predominant circulating genotype 2.VII, and the relevance of potential antigenic drift is under discussion. To investigate variation within neutralization-sensitive epitopes within the protein responsible for receptor binding, i.e. the Hemagglutinin-Neuraminidase (HN) spike protein, we were interested in establishing genotype-specific monoclonal antibodies (MAbs).

Methods: An HN-enriched fraction of a gradient-purified NDV genotype 2.VII was prepared and successfully employed to induce antibodies in BalbC mice that recognize conformationally intact sites reactive by haemagglutination inhibition (HI). For subsequent screening of mouse hybridoma cultures, an NDV-ELISA was established that utilizes Concanavalin A (ConA-ELISA) coupled glycoproteins proven to present conformation-dependent epitopes.

Results: Six out of nine selected MAbs were able to block receptor binding as demonstrated by HI activity. One MAb recognized an epitope only present in the homologue virus, while four other MAbs showed weak reactivity to selected other genotypes. On the other hand, one broadly cross-reacting MAb reacted with all genotypes tested and resembled the reactivity profile of genotype-specific polyclonal antibody preparations that point to minor antigenic differences between tested NDV genotpyes.

Conclusions: These results point to the concurrent presence of variable and conserved epitopes within the HN molecule of NDV. The described protocol should help to generate MAbs against a variety of NDV strains and to enable in depth analysis of the antigenic profiles of different genotypes.
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http://dx.doi.org/10.1186/s12985-021-01540-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8072307PMC
April 2021

Active Case Finding of Current Bornavirus Infections in Human Encephalitis Cases of Unknown Etiology, Germany, 2018-2020.

Emerg Infect Dis 2021 May;27(5):1371-1379

Human bornavirus encephalitis is a severe and often fatal infection caused by variegated squirrel bornavirus 1 (VSBV-1) and Borna disease virus 1 (BoDV-1). We conducted a prospective study of bornavirus etiology of encephalitis cases in Germany during 2018-2020 by using a serologic testing scheme applied along proposed graded case definitions for VSBV-1, BoDV-1, and unspecified bornavirus encephalitis. Of 103 encephalitis cases of unknown etiology, 4 bornavirus infections were detected serologically. One chronic case was caused by VSBV-1 after occupational-related contact of a person with exotic squirrels, and 3 acute cases were caused by BoDV-1 in virus-endemic areas. All 4 case-patients died. Bornavirus etiology could be confirmed by molecular methods. Serologic testing for these cases was virus specific, discriminatory, and a practical diagnostic option for living patients if no brain tissue samples are available. This testing should be guided by clinical and epidemiologic suspicions, such as residence in virus-endemic areas and animal exposure.
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http://dx.doi.org/10.3201/eid2705.204490DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8084505PMC
May 2021

Neuraminidase-associated plasminogen recruitment enables systemic spread of natural avian Influenza viruses H3N1.

PLoS Pathog 2021 Apr 23;17(4):e1009490. Epub 2021 Apr 23.

Institute of Diagnostic Virology, Greifswald-Insel Riems, Germany.

Repeated outbreaks due to H3N1 low pathogenicity avian influenza viruses (LPAIV) in Belgium were associated with unusually high mortality in chicken in 2019. Those events caused considerable economic losses and prompted restriction measures normally implemented for eradicating high pathogenicity avian influenza viruses (HPAIV). Initial pathology investigations and infection studies suggested this virus to be able to replicate systemically, being very atypical for H3 LPAIV. Here, we investigate the pathogenesis of this H3N1 virus and propose a mechanism explaining its unusual systemic replication capability. By intravenous and intracerebral inoculation in chicken, we demonstrate systemic spread of this virus, extending to the central nervous system. Endoproteolytic viral hemagglutinin (HA) protein activation by either tissue-restricted serine peptidases or ubiquitous subtilisin-like proteases is the functional hallmark distinguishing (H5 or H7) LPAIV from HPAIV. However, luciferase reporter assays show that HA cleavage in case of the H3N1 strain in contrast to the HPAIV is not processed by intracellular proteases. Yet the H3N1 virus replicates efficiently in cell culture without trypsin, unlike LPAIVs. Moreover, this trypsin-independent virus replication is inhibited by 6-aminohexanoic acid, a plasmin inhibitor. Correspondingly, in silico analysis indicates that plasminogen is recruitable by the viral neuraminidase for proteolytic activation due to the loss of a strongly conserved N-glycosylation site at position 130. This mutation was shown responsible for plasminogen recruitment and neurovirulence of the mouse brain-passaged laboratory strain A/WSN/33 (H1N1). In conclusion, our findings provide good evidence in natural chicken strains for N1 neuraminidase-operated recruitment of plasminogen, enabling systemic replication leading to an unusual high pathogenicity phenotype. Such a gain of function in naturally occurring AIVs representing an established human influenza HA-subtype raises concerns over potential zoonotic threats.
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http://dx.doi.org/10.1371/journal.ppat.1009490DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8118554PMC
April 2021

Recommendations for the introduction of metagenomic next-generation sequencing in clinical virology, part II: bioinformatic analysis and reporting.

J Clin Virol 2021 May 26;138:104812. Epub 2021 Mar 26.

Virology Laboratory, Genomics and Health Area, Centre for Public Health Research (FISABIO-Public Health), Valencia, Spain; Department of Microbiology, Medical School, University of Valencia, Spain; CIBERESP, Instituto de Salud Carlos III, Madrid, Spain. Electronic address:

Metagenomic next-generation sequencing (mNGS) is an untargeted technique for determination of microbial DNA/RNA sequences in a variety of sample types from patients with infectious syndromes. mNGS is still in its early stages of broader translation into clinical applications. To further support the development, implementation, optimization and standardization of mNGS procedures for virus diagnostics, the European Society for Clinical Virology (ESCV) Network on Next-Generation Sequencing (ENNGS) has been established. The aim of ENNGS is to bring together professionals involved in mNGS for viral diagnostics to share methodologies and experiences, and to develop application guidelines. Following the ENNGS publication Recommendations for the introduction of mNGS in clinical virology, part I: wet lab procedure in this journal, the current manuscript aims to provide practical recommendations for the bioinformatic analysis of mNGS data and reporting of results to clinicians.
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http://dx.doi.org/10.1016/j.jcv.2021.104812DOI Listing
May 2021

Light Sheet Microscopy-Assisted 3D Analysis of SARS-CoV-2 Infection in the Respiratory Tract of the Ferret Model.

Viruses 2021 03 23;13(3). Epub 2021 Mar 23.

Institute of Molecular Virology and Cell Biology, Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, 17493 Greifswald-Insel Riems, Germany.

The visualization of viral pathogens in infected tissues is an invaluable tool to understand spatial virus distribution, localization, and cell tropism in vivo. Commonly, virus-infected tissues are analyzed using conventional immunohistochemistry in paraffin-embedded thin sections. Here, we demonstrate the utility of volumetric three-dimensional (3D) immunofluorescence imaging using tissue optical clearing and light sheet microscopy to investigate host-pathogen interactions of pandemic SARS-CoV-2 in ferrets at a mesoscopic scale. The superior spatial context of large, intact samples (>150 mm) allowed detailed quantification of interrelated parameters like focus-to-focus distance or SARS-CoV-2-infected area, facilitating an in-depth description of SARS-CoV-2 infection foci. Accordingly, we could confirm a preferential infection of the ferret upper respiratory tract by SARS-CoV-2 and suggest clustering of infection foci in close proximity. Conclusively, we present a proof-of-concept study for investigating critically important respiratory pathogens in their spatial tissue morphology and demonstrate the first specific 3D visualization of SARS-CoV-2 infection.
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http://dx.doi.org/10.3390/v13030529DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8004956PMC
March 2021

Re-Introduction of Bovine Viral Diarrhea Virus in a Disease-Free Region: Impact on the Affected Cattle Herd and Diagnostic Implications.

Pathogens 2021 Mar 18;10(3). Epub 2021 Mar 18.

Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, 17493 Greifswald-Insel Riems, Germany.

Bovine viral diarrhea (BVD) is one of the most important infectious cattle diseases worldwide. The major source of virus transmission is immunotolerant, persistently infected (PI) calves, which makes them the key target of control programs. In the German federal state of Saxony-Anhalt, a very low prevalence was achieved, with more than 99.8% of the cattle herds being free from PI animals since the year 2013. In 2017, BVD virus was detected in a previously disease-free holding (herd size of ~380 cows, their offspring, and fattening bulls). The purchase of two so-called Trojan cows, i.e., dams pregnant with a PI calf, was identified as the source of infection. The births of the PI animals resulted in transient infections of in-contact dams, accompanied by vertical virus transmission to their fetuses within the critical timeframe for the induction of PI calves. Forty-eight days after the birth of the first PI calf, all animals in close contact with the Trojan cows during their parturition period were blood-sampled and serologically examined by a neutralization test and several commercial ELISAs. The resulting seroprevalence strongly depended on the applied test system. The outbreak could be stopped by the immediate elimination of every newborn PI calf and vaccination, and since 2018, no BVD cases have occurred.
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http://dx.doi.org/10.3390/pathogens10030360DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8002923PMC
March 2021

No hints at glyphosate-induced ruminal dysbiosis in cows.

NPJ Biofilms Microbiomes 2021 03 25;7(1):30. Epub 2021 Mar 25.

Institute of Animal Nutrition, Federal Research Institute for Animal Health, Friedrich-Loeffler-Institute, Brunswick, Germany.

Glyphosate-based herbicides are among the most used non-selective herbicides worldwide and inhibit synthesis of aromatic amino acids in plants, bacteria, and fungi. Given the broad usage, controversies concerning potential effects of glyphosate on health and especially on gut microbiomes arose. For cattle, it has been proposed based on in vitro data that glyphosate has detrimental effects on the ruminal microbiome, which manifest as a specific inhibition of bacteria involved in fiber degradation and as an enrichment of specific pathogens. In the present study, glyphosate effects on the ruminal microbiome were analyzed in vivo using glyphosate contaminated feedstuffs with strong differences in dietary fiber and dietary energy content in order to reproduce the proposed detrimental glyphosate effects on the rumen microbiome. While significant impact of dietary factors on the ruminal microbiome and its products are pointed out, no adverse glyphosate effects on ruminal microbiome composition, diversity, and microbial metabolites are observed.
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http://dx.doi.org/10.1038/s41522-021-00198-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7994389PMC
March 2021

Experimental SARS-CoV-2 Infection of Bank Voles.

Emerg Infect Dis 2021 04;27(4):1193-1195

After experimental inoculation, severe acute respiratory syndrome coronavirus 2 infection was confirmed in bank voles by seroconversion within 8 days and detection of viral RNA in nasal tissue for up to 21 days. However, transmission to contact animals was not detected. Thus, bank voles are unlikely to establish effective transmission cycles in nature.
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http://dx.doi.org/10.3201/eid2704.204945DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8007283PMC
April 2021

Challenges and Opportunities in the Use of High and Maximum Biocontainment Facilities in Developing and Licensing Risk Group 3 and Risk Group 4 Agent Veterinary Vaccines.

ILAR J 2021 Mar 13. Epub 2021 Mar 13.

Tunnell Government Services Inc., Bethesda, Maryland, USA.

New solutions are necessary for the singular global health security threat formed by endemic, epidemic, and emerging/re-emerging zoonoses, coupled with epizootic and enzootic transboundary animal diseases (TADs). This One Health issue is related to the daily interactions between wildlife, domesticated and indigenous livestock, and humans primarily associated with global trade, transboundary co-movement of humans and diverse livestock/livestock products, and agriculture production intensification and penetration into previously uninhabited areas. The World Health Organization defines Risk Group 3 (RG-3) and RG-4 pathogens as mainly viruses but also bacteria that serve as the foundation for approximately 60% of emerging infectious diseases that are zoonoses. The World Organisation for Animal Health defines trade-notifiable TADs, and subsets of these are zoonotic. Livestock vaccination policies mainly focus on TADs that are promulgated by the United Nations Food and Agriculture Organization and government agriculture agencies. The development, licensure, and product manufacturing of next-generation molecular-based RG-3 and RG-4 veterinary vaccines largely ignored by the global animal health biopharmaceutical sector can have an important positive impact on food security and One Health. There have been sharp increases in the global demand for livestock meat and milk products, especially in low- and middle-income countries in Africa and Asia. This relatively recent market driver-coupled with scientific advances in human EID and zoonotic disease vaccine platform technologies and increases in the number of high (US biosafety level 3 agriculture) and maximum (US animal biosafety level 4) biocontainment facilities with supporting workforce capabilities-offers new investment opportunities to the animal health biopharmaceutical sector. Moreover, a growing number of One Health public-private partnerships have moved the net present value calculus in favor of the financial feasibility of RG-3 and RG-4 veterinary vaccine product development and licensure. This article highlights the challenges and opportunities in the use of high and maximum biocontainment facilities in developing and licensing RG-3 and RG-4 veterinary vaccines that are safe and effective against epizootic and enzootic TADs and zoonotic diseases.
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http://dx.doi.org/10.1093/ilar/ilab004DOI Listing
March 2021

Introduction and spread of variegated squirrel bornavirus 1 (VSBV-1) between exotic squirrels and spill-over infections to humans in Germany.

Emerg Microbes Infect 2021 Dec;10(1):602-611

Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany.

The variegated squirrel bornavirus 1 (VSBV-1) is a recently discovered emerging viral pathogen which causes severe and eventually fatal encephalitis in humans after contact to exotic squirrels in private holdings and zoological gardens. Understanding the VSBV-1 epidemiology is crucial to develop, implement, and maintain surveillance strategies for the detection and control of animal and human infections. Based on a newly detected human encephalitis case in a zoological garden, epidemiological squirrel trade investigations and molecular phylogeny analyses of VSBV-1 with temporal and spatial resolution were conducted. Phylogenetic analyses indicated a recent emergence of VSBV-1 in European squirrel holdings and several animal-animal and animal-human spill-over infections. Virus phylogeny linked to squirrel trade analysis showed the introduction of a common ancestor of the known current VSBV-1 isolates into captive exotic squirrels in Germany, most likely by Prevost's squirrels (). The links of the animal trade between private breeders and zoos, the likely introduction pathway of VSBV-1 into Germany, and the role of a primary animal distributor were elucidated. In addition, a seroprevalence study was performed among zoo animal caretakers from VSBV-1 affected zoos. No seropositive healthy zoo animal caretakers were found, underlining a probable high-case fatality rate of human VSBV-1 infections. This study illustrates the network and health consequences of uncontrolled wild pet trading as well as the benefits of molecular epidemiology for elucidation and future prevention of infection chains by zoonotic viruses. To respond to emerging zoonotic diseases rapidly, improved regulation and control strategies are urgently needed.
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http://dx.doi.org/10.1080/22221751.2021.1902752DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8018504PMC
December 2021

Long-term presence of tick-borne encephalitis virus in experimentally infected bank voles (Myodes glareolus).

Ticks Tick Borne Dis 2021 07 25;12(4):101693. Epub 2021 Feb 25.

Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, Südufer 10, 17493, Greifswald, Insel Riems, Germany. Electronic address:

Tick-borne encephalitis virus (TBEV) is a vector-borne pathogen that can cause serious neurological symptoms in humans. Across large parts of Eurasia TBEV is found in three traditional subtypes: the European, the Siberian and the Far-eastern subtype. Small mammalian animals play an important role in the transmission cycle as they enable the spread of TBEV among the vector tick population. To assess the impact of TBEV infection on its natural hosts, outbred bank voles (Myodes glareolus) were inoculated with one out of four European TBEV strains. Three of these TBEV strains were recently isolated in Germany. The forth one was the TBEV reference strain Neudörfl. Sampling points at 7, 14, 28, and 56 days post inoculation allowed the characterization of the course of infection. At each time point, six animals per strain were euthanized and eleven organ samples (brain, spine, lung, heart, small and large intestine, liver, spleen, kidney, bladder, sexual organ) as well as whole blood and serum samples were collected. The majority of bank voles (92/96) remained clinically unaffected after the inoculation with TBEV, but still developed a systemic infection during the first week, which transitioned to a viraemia and an infestation of the brain in some animals for the remainder of the first month. Viral RNA was found in whole blood samples of several animals (50/96), but only in a small fraction of the corresponding serum samples (4/50). From the whole blood, virus was successfully reisolated in cell culture until 14 days after inoculation. Less than five percent of all inoculated bank voles (4/96) displayed signs of distress in combination with a rapid weight loss and had to be euthanized prematurely. Overall, the recently isolated TBEV strains showed marked differences, such as a more frequent development of long-term viraemia and a higher detection rate of viral RNA in various organs, in comparison to the reference strain Neudörfl. Overall, our data suggest that the bank vole is a potential amplifying host in the TBEV transmission cycle and appears to be highly adapted to circulating TBEV strains.
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http://dx.doi.org/10.1016/j.ttbdis.2021.101693DOI Listing
July 2021

Swift and Reliable "Easy Lab" Methods for the Sensitive Molecular Detection of African Swine Fever Virus.

Int J Mol Sci 2021 Feb 25;22(5). Epub 2021 Feb 25.

Friedrich-Loeffler-Institut, Institute of Diagnostic Virology, 17493 Greifswald-Insel Riems, Germany.

African swine fever (ASF) is a contagious viral hemorrhagic disease of domestic pigs and wild boars. The disease is notifiable to the World Organisation for Animal Health (OIE) and is responsible for high mortality and serious economic losses. PCR and real-time PCR (qPCR) are the OIE-recommended standard methods for the direct detection of African swine fever virus (ASFV) DNA. The aim of our work was the simplification and standardization of the molecular diagnostic workflow in the lab. For validation of this "easy lab" workflow, different sample materials from animal trials were collected and analyzed (EDTA blood, serum, oral swabs, chewing ropes, and tissue samples) to identify the optimal sample material for diagnostics in live animals. Based on our data, the EDTA blood samples or bloody tissue samples represent the best specimens for ASFV detection in the early and late phases of infection. The application of prefilled ready-to-use reagents for nucleic acid extraction or the use of a Tissue Lysis Reagent (TLR) delivers simple and reliable alternatives for the release of the ASFV nucleic acids. For the qPCR detection of ASFV, different published and commercial kits were compared. Here, a lyophilized commercial kit shows the best results mainly based on the increased template input. The good results of the "easy lab" strategy could be confirmed by the ASFV detection in field samples from wild boars collected from the 2020 ASFV outbreak in Germany. Appropriate internal control systems for extraction and PCR are key features of the "easy lab" concept and reduce the risk of false-negative and false-positive results. In addition, the use of easy-to-handle machines and software reduces training efforts and the misinterpretation of results. The PCR diagnostics based on the "easy lab" strategy can realize a high sensitivity and specificity comparable to the standard PCR methods and should be especially usable for labs with limited experiences and resources.
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http://dx.doi.org/10.3390/ijms22052307DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7956467PMC
February 2021

Economic evaluation of whole genome sequencing for pathogen identification and surveillance - results of case studies in Europe and the Americas 2016 to 2019.

Euro Surveill 2021 Mar;26(9)

Friedrich-Loeffler-Institut, Greifswald, Germany.

BackgroundWhole genome sequencing (WGS) is increasingly used for pathogen identification and surveillance.AimWe evaluated costs and benefits of routine WGS through case studies at eight reference laboratories in Europe and the Americas which conduct pathogen surveillance for avian influenza (two laboratories), human influenza (one laboratory) and food-borne pathogens (five laboratories).MethodsThe evaluation focused on the institutional perspective, i.e. the 'investment case' for implementing WGS compared with conventional methods, based on costs and benefits during a defined reference period, mostly covering at least part of 2017. A break-even analysis estimated the number of cases of illness (for the example of surveillance) that would need to be avoided through WGS in order to 'break even' on costs.ResultsOn a per-sample basis, WGS was between 1.2 and 4.3 times more expensive than routine conventional methods. However, WGS brought major benefits for pathogen identification and surveillance, substantially changing laboratory workflows, analytical processes and outbreaks detection and control. Between 0.2% and 1.1% (on average 0.7%) of reported salmonellosis cases would need to be prevented to break even with respect to the additional costs of WGS.ConclusionsEven at cost levels documented here, WGS provides a level of additional information that more than balances the additional costs if used effectively. The substantial cost differences for WGS between reference laboratories were due to economies of scale, degree of automation, sequencing technology used and institutional discounts for equipment and consumables, as well as the extent to which sequencers are used at full capacity.
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http://dx.doi.org/10.2807/1560-7917.ES.2021.26.9.1900606DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7934224PMC
March 2021

Co-infections: Simultaneous detections of West Nile virus and Usutu virus in birds from Germany.

Transbound Emerg Dis 2021 Mar 2. Epub 2021 Mar 2.

Institute of Novel and Emerging Infectious Diseases, Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, Greifswald-Insel Riems, Germany.

The emergence of West Nile virus (WNV) and Usutu virus (USUV) in Europe resulted in significant outbreaks leading to avifauna mortality and human infections. Both viruses have overlapping geographical, host and vector ranges, and are often co-circulating in Europe. In Germany, a nationwide bird surveillance network was established to monitor these zoonotic arthropod-borne viruses in migratory and resident birds. In this framework, co-infections with WNV and USUV were detected in six dead birds collected in 2018 and 2019. Genomic sequencing and phylogenetic analyses classified the detected WNV strains as lineage 2 and the USUV strains as lineages Africa 2 (n = 2), Africa 3 (n = 3) and Europe 2 (n = 1). Preliminary attempts to co-propagate both viruses in vitro failed. However, we successfully cultivated WNV from two animals. Further evidence for WNV-USUV co-infection was obtained by sampling live birds in four zoological gardens with confirmed WNV cases. Three snowy owls had high neutralizing antibody titres against both WNV and USUV, of which two were also positive for USUV-RNA. In conclusion, further reports of co-infections in animals as well as in humans are expected in the future, particularly in areas where both viruses are present in the vector population.
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http://dx.doi.org/10.1111/tbed.14050DOI Listing
March 2021

SARS-CoV-2 spike D614G change enhances replication and transmission.

Nature 2021 04 26;592(7852):122-127. Epub 2021 Feb 26.

Institute of Virology and Immunology (IVI), Mittelhäusern, Switzerland.

During the evolution of SARS-CoV-2 in humans, a D614G substitution in the spike glycoprotein (S) has emerged; virus containing this substitution has become the predominant circulating variant in the COVID-19 pandemic. However, whether the increasing prevalence of this variant reflects a fitness advantage that improves replication and/or transmission in humans or is merely due to founder effects remains unknown. Here we use isogenic SARS-CoV-2 variants to demonstrate that the variant that contains S(D614G) has enhanced binding to the human cell-surface receptor angiotensin-converting enzyme 2 (ACE2), increased replication in primary human bronchial and nasal airway epithelial cultures as well as in a human ACE2 knock-in mouse model, and markedly increased replication and transmissibility in hamster and ferret models of SARS-CoV-2 infection. Our data show that the D614G substitution in S results in subtle increases in binding and replication in vitro, and provides a real competitive advantage in vivo-particularly during the transmission bottleneck. Our data therefore provide an explanation for the global predominance of the variant that contains S(D614G) among the SARS-CoV-2 viruses that are currently circulating.
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http://dx.doi.org/10.1038/s41586-021-03361-1DOI Listing
April 2021

Human Infection with Eurasian Avian-Like Swine Influenza A(H1N1) Virus, the Netherlands, September 2019.

Emerg Infect Dis 2021 Mar;27(3):939-943

We report a zoonotic infection of a pig farmer in the Netherlands with a Eurasian avian-like swine influenza A(H1N1) virus that was also detected in the farmed pigs. Both viruses were antigenically and genetically characterized. Continued surveillance of swine influenza A viruses is needed for risk assessment in humans and swine.
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http://dx.doi.org/10.3201/eid2703.201863DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7920694PMC
March 2021

Next-generation diagnostics: virus capture facilitates a sensitive viral diagnosis for epizootic and zoonotic pathogens including SARS-CoV-2.

Microbiome 2021 02 20;9(1):51. Epub 2021 Feb 20.

Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, Südufer 10, 17493, Greifswald-Insel Riems, Germany.

Background: The detection of pathogens in clinical and environmental samples using high-throughput sequencing (HTS) is often hampered by large amounts of background information, which is especially true for viruses with small genomes. Enormous sequencing depth can be necessary to compile sufficient information for identification of a certain pathogen. Generic HTS combining with in-solution capture enrichment can markedly increase the sensitivity for virus detection in complex diagnostic samples.

Methods: A virus panel based on the principle of biotinylated RNA baits was developed for specific capture enrichment of epizootic and zoonotic viruses (VirBaits). The VirBaits set was supplemented by a SARS-CoV-2 predesigned bait set for testing recent SARS-CoV-2-positive samples. Libraries generated from complex samples were sequenced via generic HTS (without enrichment) and afterwards enriched with the VirBaits set. For validation, an internal proficiency test for emerging epizootic and zoonotic viruses (African swine fever virus, Ebolavirus, Marburgvirus, Nipah henipavirus, Rift Valley fever virus) was conducted.

Results: The VirBaits set consists of 177,471 RNA baits (80-mer) based on about 18,800 complete viral genomes targeting 35 epizootic and zoonotic viruses. In all tested samples, viruses with both DNA and RNA genomes were clearly enriched ranging from about 10-fold to 10,000-fold for viruses including distantly related viruses with at least 72% overall identity to viruses represented in the bait set. Viruses showing a lower overall identity (38% and 46%) to them were not enriched but could nonetheless be detected based on capturing conserved genome regions. The internal proficiency test supports the improved virus detection using the combination of HTS plus targeted enrichment but also points to the risk of cross-contamination between samples.

Conclusions: The VirBaits approach showed a high diagnostic performance, also for distantly related viruses. The bait set is modular and expandable according to the favored diagnostics, health sector, or research question. The risk of cross-contamination needs to be taken into consideration. The application of the RNA-baits principle turned out to be user friendly, and even non-experts can easily use the VirBaits workflow. The rapid extension of the established VirBaits set adapted to actual outbreak events is possible as shown for SARS-CoV-2. Video abstract.
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http://dx.doi.org/10.1186/s40168-020-00973-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7896545PMC
February 2021

A modified live bat influenza A virus-based vaccine prototype provides full protection against HPAIV H5N1.

NPJ Vaccines 2020 May 15;5(1):40. Epub 2020 May 15.

Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, Greifswald-Insel Riems, Germany.

Highly pathogenic avian influenza viruses (HPAIVs) of subtype H5 are a major threat for poultry holdings worldwide, here especially the zoonotic Asian H5N1 viruses. These HPAIVs have caused more than 500 fatal spillover infections from poultry to humans, with a looming danger of a new pandemic by establishing human-to-human transmissions. Besides culling measures in infected farms in endemic areas, vaccination is the major tool against HPAIV. However, the mainly used inactivated preparations have several limitations, like application to the individual animal by injection and a reduced efficiency. Here we present a modified live influenza vaccine prototype, which is based on the H17N10 bat influenza virus. The new chimeric vaccine strain R65/H17N10 was able to provide full protection against a lethal challenge infection with HPAIV H5N1 of juvenile and subadult chickens, as well as ferrets after oronasal immunization. In addition, the H5 vaccine prototype cannot reassort with avian influenza viruses and therefore is a promising tool against HPAIV H5 infection, allowing new vaccination strategies for efficient disease control.
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http://dx.doi.org/10.1038/s41541-020-0185-6DOI Listing
May 2020

African Swine Fever Laboratory Diagnosis-Lessons Learned from Recent Animal Trials.

Pathogens 2021 Feb 6;10(2). Epub 2021 Feb 6.

Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, 17493 Greifswald-Insel Riems, Germany.

African swine fever virus (ASFV) causes a hemorrhagic disease in pigs with high socio-economic consequences. To lower the impact of disease incursions, early detection is crucial. In the context of experimental animal trials, we evaluated diagnostic workflows for a high sample throughput in active surveillance, alternative sample matrices for passive surveillance, and lateral flow devices (LFD) for rapid testing. We could demonstrate that EDTA blood is significantly better suited for early ASFV detection than serum. Tissues recommended by the respective diagnostic manuals were in general comparable in their performance, with spleen samples giving best results. Superficial lymph nodes, ear punches, and different blood swabs were also evaluated as potential alternatives. In summary, all matrices yielded positive results at the peak of clinical signs and could be fit for purpose in passive surveillance. However, weaknesses were discovered for some matrices when it comes to the early phase of infection or recovery. The antigen LFD showed variable results with best performance in the clinical phase. The antibody LFD was quite comparable with ELISA systems. Concluding, alternative approaches are feasible but have to be embedded in control strategies selecting test methods and sample materials following a "fit-for-purpose" approach.
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http://dx.doi.org/10.3390/pathogens10020177DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7915929PMC
February 2021

High genetic variability of Schmallenberg virus M-segment leads to efficient immune escape from neutralizing antibodies.

PLoS Pathog 2021 01 26;17(1):e1009247. Epub 2021 Jan 26.

Institute of Diagnostic Virology, Friedrich-Loeffler-Institut, Greifswald-Insel Riems, Germany.

Schmallenberg virus (SBV) is the cause of severe fetal malformations when immunologically naïve pregnant ruminants are infected. In those malformed fetuses, a "hot-spot"-region of high genetic variability within the N-terminal region of the viral envelope protein Gc has been observed previously, and this region co-localizes with a known key immunogenic domain. We studied a series of M-segments of those SBV variants from malformed fetuses with point mutations, insertions or large in-frame deletions of up to 612 nucleotides. Furthermore, a unique cell-culture isolate from a malformed fetus with large in-frame deletions within the M-segment was analyzed. Each Gc-protein with amino acid deletions within the "hot spot" of mutations failed to react with any neutralizing anti-SBV monoclonal antibodies or a domain specific antiserum. In addition, in vitro virus replication of the natural deletion variant could not be markedly reduced by neutralizing monoclonal antibodies or antisera from the field. The large-deletion variant of SBV that could be isolated in cell culture was highly attenuated with an impaired in vivo replication following the inoculation of sheep. In conclusion, the observed amino acid sequence mutations within the N-terminal main immunogenic domain of glycoprotein Gc result in an efficient immune evasion from neutralizing antibodies in the special environment of a developing fetus. These SBV-variants were never detected as circulating viruses, and therefore should be considered to be dead-end virus variants, which are not able to spread further. The observations described here may be transferred to other orthobunyaviruses, particularly those of the Simbu serogroup that have been shown to infect fetuses. Importantly, such mutant strains should not be included in attempts to trace the spatial-temporal evolution of orthobunyaviruses in molecular-epidemiolocal approaches during outbreak investigations.
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http://dx.doi.org/10.1371/journal.ppat.1009247DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7872300PMC
January 2021