Diagnosis and Pathogenesis of Nairobi Sheep Disease Orthonairovirus Infections in Sheep and Cattle

Generation and Characterisation of Monoclonal Antibodies against Nairobi Sheep Disease Virus Nucleoprotein

Nairobi sheep disease (NSD), caused by the viral agent NSD virus (NSDV), is a haemorrhagic fever disease affecting and inducing high mortality in sheep and goat populations. NSDV belongs to the genus Orthonairovirus of the Nairoviridae family from the order Bunyavirales. Other viruses circulating in livestock such as Crimean-Congo haemorrhagic fever virus (CCHFV) and Dugbe virus (DUGV) are members of the same genus and are reported to share antigenic features. There are very few available materials to study NSDV infection both in vitro and in vivo. In the present work, we characterised two monoclonal antibodies generated in mice that recognise NSDV specifically but not CCHFV or DUGV, along with a potential use to define virus-infected cells, using flow cytometry. We believe this tool can be useful for research, but also NSDV diagnostics, especially through immunological staining.

The proprotein convertase SKI-1/S1P is a critical host factor for Nairobi sheep disease virus infectivity

Nairobi sheep disease virus (NSDV) belongs to the Orthonairovirus genus in the Bunyavirales order and is genetically related to human-pathogenic Crimean-Congo hemorrhagic fever virus (CCHFV). NSDV is a zoonotic pathogen transmitted by ticks and primarily affects naïve small ruminants in which infection leads to severe and often fatal hemorrhagic gastroenteritis. Despite its veterinary importance and the striking similarities in the clinical picture between NSDV-infected ruminants and CCHFV patients, the molecular pathogenesis of NSDV and its interactions with the host cell are largely unknown. Here, we identify the membrane-bound proprotein convertase site-1 protease (S1P), also known as subtilisin/kexin-isozyme-1 (SKI-1), as a host factor affecting NSDV infectivity. Absence of S1P in SRD-12B cells, a clonal CHO-K1 cell variant with a genetic defect in the S1P gene (MBTPS1), results in significantly decreased NSDV infectivity while transient complementation of SKI-1/S1P rescues NSDV infection. SKI-1/S1P is dispensable for virus uptake but critically required for production of infectious virus progeny. Moreover, we provide evidence that SKI-1/S1P is involved in the posttranslational processing of the NSDV glycoprotein precursor. Our results demonstrate the role of SKI-1/S1P in the virus life cycle of NSDV and suggest that this protease is a common host factor for orthonairoviruses and may thus represent a promising broadly-effective, indirect antiviral target.

Whole-Genome Sequencing of Six Neglected Arboviruses Circulating in Africa Using Sequence-Independent Single Primer Amplification (SISPA) and MinION Nanopore Technologies

On the African continent, a large number of arthropod-borne viruses (arboviruses) with zoonotic potential have been described, and yet little is known of most of these pathogens, including their actual distribution or genetic diversity. In this study, we evaluated as a proof-of-concept the effectiveness of the nonspecific sequencing technique sequence-independent single primer amplification (SISPA) on third-generation sequencing techniques (MinION sequencing, Oxford Nanopore Technologies, Oxford, UK) by comparing the sequencing results from six different samples of arboviruses known to be circulating in Africa (Crimean-Congo hemorrhagic fever virus (CCHFV), Rift Valley fever virus (RVFV), Dugbe virus (DUGV), Nairobi sheep disease virus (NSDV), Middleburg virus (MIDV) and Wesselsbron virus (WSLV)). All sequenced samples were derived either from previous field studies or animal infection trials. Using this approach, we were able to generate complete genomes for all six viruses without the need for virus-specific whole-genome PCRs. Higher Cq values in diagnostic RT-qPCRs and the origin of the samples (from cell culture or animal origin) along with their quality were found to be factors affecting the success of the sequencing run. The results of this study may stimulate the use of metagenomic sequencing approaches, contributing to a better understanding of the genetic diversity of neglected arboviruses.

Virus-host interactions during tick-borne bunyavirus infection

The Bunyavirales order is the largest grouping of RNA viruses, comprising emerging and re-emerging human, plant and animal pathogens. Bunyaviruses have a global distribution and many members of the order are transmitted by arthropods. They have evolved a plethora of mechanisms to manipulate the regulatory processes of the infected cell to facilitate their own replicative cycle, in hosts of disparate phylogenies. Interest in virus-vector interactions is growing rapidly. However, current understanding of tick-borne bunyavirus cellular interaction is heavily biased to studies conducted in mammalian systems. In this short review, we summarise current understandings of how tick-borne bunyaviruses utilise major cellular pathways (innate immunity, apoptosis and RNAi responses) in mammalian or tick cells to facilitate virus replication.

The Relationship between DUGBE Virus Infection and Autophagy in Epithelial Cells

Dugbe orthonairovirus (DUGV) is a tick-borne arbovirus within the order Bunyavirales. Although displaying mild pathogenic potential, DUGV is genetically related to the Crimean–Congo hemorrhagic fever virus (CCHFV), another orthonairovirus that causes severe liver dysfunction and hemorrhagic fever with a high mortality rate in humans. As we previously observed that CCHFV infection could massively recruit and lipidate MAP1LC3 (LC3), a core factor involved in the autophagic degradation of cytosolic components, we asked whether DUGV infection also substantially impacts the autophagy machinery in epithelial cells. We observed that DUGV infection does impose LC3 lipidation in cultured hepatocytes. DUGV infection also caused an upregulation of the MAP1LC3 and SQSTM1/p62 transcript levels, which were, however, more moderate than those seen during CCHFV infection. In contrast, unlike during CCHFV infection, the modulation of core autophagy factors could influence both LC3 lipidation and viral particle production: the silencing of ATG5 and/or ATG7 diminished the induction of LC3 lipidation and slightly upregulated the level of infectious DUGV particle production. Overall, the results are compatible with the notion that in epithelial cells infected with DUGV in vitro, the autophagy machinery may be recruited to exert a certain level of restriction on viral replication. Thus, the relationship between DUGV infection and autophagy in epithelial cells appears to present both similarities and distinctions with that seen during CCHFV infection.

Deciphering Antibody Responses to Orthonairoviruses in Ruminants

Antibody cross-reactivities between related viruses are common diagnostic challenges, resulting in reduced diagnostic specificities and sensitivities. In this study, antibody cross-reactions between neglected members of the genus Orthonairovirus-Hazara (HAZV), Dugbe (DUGV), and Nairobi sheep disease orthonairovirus (NSDV)-were investigated. Mono-specific ovine and bovine sera following experimental infections as well immunization trials with HAZV, DUGV, and NSDV were tested in homologous and heterologous virus-specific assays, namely indirect ELISAs based on recombinant N protein, indirect immunofluorescence assays (iIFA), and two neutralization test formats (plaque reduction neutralization test (PRNT) and micro-virus neutralization test (mVNT)). The highest specificities were achieved with the ELISAs, followed by the mVNT, iIFA, and PRNT. Cross-reactivities were mainly observed within the Nairobi sheep disease serogroup-but surprisingly, HAZV antibodies in PRNT did also neutralize NSDV and DUGV. In conclusion, we recommend ELISAs and mVNTs for a discriminative diagnostic approach to differentiate between these antibodies. NSDV antisera were also used in serological assays for the detection of antibodies against the human pathogen Crimean-Congo hemorrhagic fever orthonairovirus (CCHFV). Interestingly, all CCHFV ELISAs (In-house and commercial) achieved high diagnostic specificities, whereas significant cross-reactivities were observed in a CCHFV iIFA. Previously, similar results were obtained when analyzing the HAZV and DUGV antisera.