Mechanism of reduction of virus release and cell-cell fusion in persistent canine distemper virus infection

Canine distemper virus (CDV), a mobillivirus related to measles virus causes a chronic progressive demyelinating disease, associated with persistence of the virus in the central nervous system (CNS). CNS persistence of morbilliviruses has been associated with cell-to-cell spread, thereby limiting immune detection. The mechanism of cell-to-cell spread remains uncertain. In the present study we studied viral spread comparing a cytolytic (non-persistent) and a persistent CDV strain in cell cultures. Cytolytic CDV spread in a compact concentric manner with extensive cell fusion and destruction of the monolayer. Persistent CDV exhibited a heterogeneous cell-to-cell pattern of spread without cell fusion and 100-fold reduction of infectious viral titers in supernatants as compared to the cytolytic strain. Ultrastructurally, low infectious titers correlated with limited budding of persistent CDV as compared to the cytolytic strain, which shed large numbers of viral particles. The pattern of heterogeneous cell-to-cell viral spread can be explained by low production of infectious viral particles in only few areas of the cell membrane. In this way persistent CDV only spreads to a small proportion of the cells surrounding an infected one. Our studies suggest that both cell-to-cell spread and limited production of infectious virus are related to reduced expression of fusogenic complexes in the cell membrane. Such complexes consist of a synergistic configuration of the attachment (H) and fusion (F) proteins on the cell surface. F und H proteins exhibited a marked degree of colocalization in cytolytic CDV infection but not in persistent CDV as seen by confocal laser microscopy. In addition, analysis of CDV F protein expression using vaccinia constructs of both strains revealed an additional large fraction of uncleaved fusion protein in the persistent strain. This suggests that the paucity of active fusion complexes is due to restricted intracellular processing of the viral fusion protei

European survey on laboratory preparedness, response and diagnostic capacity for crimean-congo haemorrhagic fever, 2012

Crimean-Congo haemorrhagic fever (CCHF) is an infectious viral disease that has (re-)emerged in the last decade in south-eastern Europe, and there is a risk for further geographical expansion to western Europe. Here we report the results of a survey covering 28 countries, conducted in 2012 among the member laboratories of the European Network for Diagnostics of 'Imported' Viral Diseases (ENIVD) to assess laboratory preparedness and response capacities for CCHF. The answers of 31 laboratories of the European region regarding CCHF case definition, training necessity, biosafety, quality assurance and diagnostic tests are presented. In addition, we identifi

Specialist laboratory networks as preparedness and response tool - The emerging viral diseases-expert laboratory network and the chikungunya outbreak, Thailand, 2019

We illustrate the potential for specialist laboratory networks to be used as preparedness and response tool through rapid collection and sharing of data. Here, the Emerging Viral Diseases-Expert Laboratory Network (EVD-LabNet) and a laboratory assessment of chikungunya virus (CHIKV) in returning European travellers related to an ongoing outbreak in Thailand was used for this purpose. EVD-LabNet rapidly collected data on laboratory requests, diagnosed CHIKV imported cases and sequences generated, and shared among its members and with the European Centre for Disease Prevention and Control. Data across the network showed an increase in CHIKV imported cases during 1 October 2018-30 April 2019 vs the same period in 2018 (172 vs 50), particularly an increase in cases known to be related to travel to Thailand (72 vs 1). Moreover, EVD-LabNet showed that strains were imported from Thailand that cluster with strains of the ECSA-IOL E1 A226 variant emerging in Pakistan in 2016 and involved in the 2017 outbreaks in Italy. CHIKV diagnostic requests increased by 23.6% between the two periods. The impact of using EVD-LabNet or similar networks as preparedness and response tool could be improved by standardisation of the collection, quality and mining of data in routine laboratory management systems

Sequence Analysis and Expression of the Attachment and Fusion Proteins of Canine Distemper Virus Wild-Type Strain A75/17

The biological properties of wild-type A75/17 and cell culture-adapted Onderstepoort canine distemper virus differ markedly. To learn more about the molecular basis for these differences, we have isolated and sequenced the protein-coding regions of the attachment and fusion proteins of wild-type canine distemper virus strain A75/17. In the attachment protein, a total of 57 amino acid differences were observed between the Onderstepoort strain and strain A75/17, and these were distributed evenly over the entire protein. Interestingly, the attachment protein of strain A75/17 contained an extension of three amino acids at the C terminus. Expression studies showed that the attachment protein of strain A75/17 had a higher apparent molecular mass than the attachment protein of the Onderstepoort strain, in both the presence and absence of tunicamycin. In the fusion protein, 60 amino acid differences were observed between the two strains, of which 44 were clustered in the much smaller F2 portion of the molecule. Significantly, the AUG that has been proposed as a translation initiation codon in the Onderstepoort strain is an AUA codon in strain A75/17. Detailed mutation analyses showed that both the first and second AUGs of strain A75/17 are the major translation initiation sites of the fusion protein. Similar analyses demonstrated that, also in the Onderstepoort strain, the first two AUGs are the translation initiation codons which contribute most to the generation of precursor molecules yielding the mature form of the fusion protein

A molecular based diagnosis of positive blood culture in the context of viral haemorrhagic fever: proof of concept

The aim of this study was to evaluate the possibility of using a PCR-based panel to identify bacterial and fungal bloodstream infections in the setting of suspected or confirmed viral haemorrhagic fever

Simultaneous detection of parainfluenza viruses 1 and 3 by real-time reverse transcription-polymerase chain reaction

Human parainfluenza virus (HPIV) types 1 and 3 are major viral pathogens responsible for upper and lower respiratory tract infections. The diagnosis of these two species is achieved generally by specific reverse transcription-polymerase chain (RT-PCR) reaction methods. In this study, a real-time RT-PCR was developed using a common pair of primers-probe (HPIV-1+3) for the simultaneous detection of both HPIV-1 and HPIV-3 genomes. Results obtained in a 10-fold dilution series assay demonstrate a high sensitivity of the assay with a lowest detection limit of approximately one plasmid copy for both HPIV-1 and HPIV-3. A comparison of HPIV-1 and HPIV-3 clinical sample detection between specific HPIV-1/HPIV-3 pairs of primers-probes and the HPIV-1+3 combination clearly shows that the latter is significantly more sensitive (gain of about five threshold cycles) than the former for HPIV-3 detection, while equivalent values are observed for HPIV-1. The HPIV-1+3 combination constitutes a more rapid, more sensitive, and less expensive alternative than classical or multiplex real-time RT-PCR assays usually used in clinical laboratories

Signal Peptide and Helical Bundle Domains of Virulent Canine Distemper Virus Fusion Protein Restrict Fusogenicity▿

Persistence in canine distemper virus (CDV) infection is correlated with very limited cell-cell fusion and lack of cytolysis induced by the neurovirulent A75/17-CDV compared to that of the cytolytic Onderstepoort vaccine strain. We have previously shown that this difference was at least in part due to the amino acid sequence of the fusion (F) protein (P. Plattet, J. P. Rivals, B. Zuber, J. M. Brunner, A. Zurbriggen, and R. Wittek, Virology 337:312-326, 2005). Here, we investigated the molecular mechanisms of the neurovirulent CDV F protein underlying limited membrane fusion activity. By exchanging the signal peptide between both F CDV strains or replacing it with an exogenous signal peptide, we demonstrated that this domain controlled intracellular and consequently cell surface protein expression, thus indirectly modulating fusogenicity. In addition, by serially passaging a poorly fusogenic virus and selecting a syncytium-forming variant, we identified the mutation L372W as being responsible for this change of phenotype. Intriguingly, residue L372 potentially is located in the helical bundle domain of the F1 subunit. We showed that this mutation drastically increased fusion activity of F proteins of both CDV strains in a signal peptide-independent manner. Due to its unique structure even among morbilliviruses, our findings with respect to the signal peptide are likely to be specifically relevant to CDV, whereas the results related to the helical bundle add new insights to our growing understanding of this class of F proteins. We conclude that different mechanisms involving multiple domains of the neurovirulent A75/17-CDV F protein act in concert to limit fusion activity, preventing lysis of infected cells, which ultimately may favor viral persistence

Synergistic inhibition in cell-cell fusion mediated by the matrix and nucleocapsid protein of canine distemper virus

Canine distemper virus (CDV) causes a chronic, demyelinating, progressive or relapsing neurological disease in dogs, because CDV persists in the CNS. Persistence of virulent CDV, such as the A75/17 strain has been reproduced in cell cultures where it is associated with a non-cytolytic infection with very limited cell-cell fusion. This is in sharp contrast to attenuated CDV infection in cell cultures, such as the Onderstepoort (OP) CDV strain, which produces extensive fusion activity and cytolysis. Fusion efficiency may be determined by the structure of the viral fusion protein per se but also by its interaction with other structural proteins of CDV. This was studied by combining genes derived from persistent and non-persistent CDV strains in transient transfection experiments. It was found that fusion efficiency was markedly attenuated by the structure of the fusion protein of the neurovirulent A75/17-CDV. Moreover, we showed that the interaction of the surface glycoproteins with the M protein of the persistent strain greatly influenced fusion activity. Site directed mutagenesis showed that the c-terminus of the M protein is of particular importance in this respect. Interestingly, although the nucleocapsid protein alone did not affect F/H-induced cell-cell fusion, maximal inhibition occurred when the latter was added to combined glycoproteins with matrix protein. Thus, the present study suggests that very limited fusogenicity in virulent CDV infection, which favours persistence by limiting cell destruction involves complex interactions between all viral structural proteins

Ebola virus disease diagnosis by real-time RT-PCR: A comparative study of 11 different procedures

The diagnosis of Ebola virus disease relies on the detection of viral RNA in blood by real-time reverse-transcription PCR. While several of these assays were developed during the unprecedented 2013-2015 Ebola virus disease outbreak in West Africa, few were applied in the field