Do birds play a role in the transmission of Toscana virus? Initial isolation results from birds in northernmost Türkiye

AIMS

Recent research has prioritized emerging and re-emerging diseases that affect human and animal health, particularly to describe how these diseases enter countries and determine their transmission cycles. Given that migratory birds play a significant role in spreading infections, the present study analysed their migration paths and specimens to investigate Orthoflavivirus, Orthonairovirus, Alphavirus and Phlebovirus in birds in Samsun province, Türkiye.

METHODS AND RESULTS

For these viruses, 312 samples from 56 birds were analysed using RT-PCR and qRT-PCR. Toscana virus (TOSV) was identified in 14 birds (four mallards, five partridges, four quails and one pigeon), representing 25% of the birds sampled. Genotype B was reported in all 14 birds. After inoculating the positive tissues in cell cultures, TOSV was isolated from the organs of pigeons, mallards and partridges.

CONCLUSIONS

This is the first time TOSV has been isolated in cell culture from birds and indicates that they may play a role in spreading TOSV in Türkiye. The results also suggest that TOSV might be carried between countries by migratory birds.

Structural flexibility of Toscana virus nucleoprotein in the presence of a single-chain camelid antibody

Phenuiviridae nucleoprotein is the main structural and functional component of the viral cycle, protecting the viral RNA and mediating the essential replication/transcription processes. The nucleoprotein (N) binds the RNA using its globular core and polymerizes through the N-terminus, which is presented as a highly flexible arm, as demonstrated in this article. The nucleoprotein exists in an `open' or a `closed' conformation. In the case of the closed conformation the flexible N-terminal arm folds over the RNA-binding cleft, preventing RNA adsorption. In the open conformation the arm is extended in such a way that both RNA adsorption and N polymerization are possible. In this article, single-crystal X-ray diffraction and small-angle X-ray scattering were used to study the N protein of Toscana virus complexed with a single-chain camelid antibody (VHH) and it is shown that in the presence of the antibody the nucleoprotein is unable to achieve a functional assembly to form a ribonucleoprotein complex.

Urine: A Pitfall for Molecular Detection of Toscana Virus? An Analytical Proof-of-Concept Study

Toscana virus (TOSV), a sandfly-borne virus, is an important etiological agent in human acute meningitis and meningoencephalitis in the Mediterranean area during the summer. However, the actual number of TOSV infections is underestimated. Laboratory confirmation is necessary because TOSV infection has overlapping clinical features with other neuro-invasive viral infections. Nowadays, the reference test for direct diagnosis in the acute phase of TOSV infection is the PCR based method for detecting TOSV in cerebrospinal fluid and/or plasma, serum, or blood. Although poorly employed, urine is another helpful biological matrix for TOSV detection. Urine is a matrix rich in PCR inhibitors that affect PCR efficiency; consequently, false negatives could be generated. To investigate the potential effect of urine PCR inhibitors on TOSV detection, we compared undiluted and diluted urine using 10-fold series of spiked TOSV. The results showed a significant improvement in TOSV detection performance in diluted urine (1 TCID50 vs. 1 × 104 TCID50 limit of detection and 101.35% vs. 129.62% efficiency, respectively, in diluted and undiluted urine). In conclusion, our data provide preliminary important insights into the use of diluted urine to limit the impact of the inhibitory effects of urine on the detection of TOSV in RT-PCR-based approaches.

Untargeted metagenomic sequencing identifies Toscana virus in patients with idiopathic meningitis, southern Spain, 2015 to 2019

BackgroundVarious pathogens, including bacteria, fungi, parasites, and viruses can lead to meningitis. Among viruses causing meningitis, Toscana virus (TOSV), a phlebovirus, is transmitted through sandfly bites. TOSV infection may be suspected if patients with enterovirus- and herpesvirus-negative aseptic (non-bacterial) meningitis recall recent insect bites. Other epidemiological factors (season, rural area) may be considered. The broad range of possible meningitis aetiologies poses considerable diagnosis challenges. Untargeted metagenomic next-generation sequencing (mNGS) can potentially identify pathogens, which are not considered or detected in routine diagnostic panels.AimIn this retrospective, single-centre observational study, we investigated mNGS usefulness to understand the cause of meningitis when conventional approaches fail.MethodsCerebrospinal fluid (CSF) samples from patients hospitalised in southern Spain in 2015-2019 with aseptic meningitis and no aetiology found by conventional testing, were subjected to mNGS. Patients' demographic characteristics had been recorded and physicians had asked them about recent insect bites. Obtained viral genome sequences were phylogenetically analysed.ResultsAmong 23 idiopathic cases, TOSV was identified in eight (all male; median age:  39 years, range: 15-78 years). Five cases lived in an urban setting, three occurred in autumn and only one recalled insect bites. Phylogenetic analysis of TOSV segment sequences supported one intra-genotype reassortment event.ConclusionsOur study highlights the usefulness of mNGS for identifying viral pathogens directly in CSF. In southern Spain, TOSV should be considered regardless of recalling of insect bites or other epidemiological criteria. Detection of a disease-associated reassortant TOSV emphasises the importance of monitoring the spread and evolution of phleboviruses in Mediterranean countries.

Infectious Toscana Virus in Seminal Fluid of Young Man Returning from Elba Island, Italy

We report detecting infectious Toscana virus in the seminal fluid of a 25-year-old man from Italy returning from Elba Island. The presence of infectious virus in human semen adds Toscana virus to the long list of viruses detected in this genital fluid and indicates a potential for sexual transmission.

Incubation Period for Neuroinvasive Toscana Virus Infections

Toscana virus (TOSV) is an emerging pathogen in the Mediterranean area and is neuroinvasive in its most severe form. Basic knowledge on TOSV biology is limited. We conducted a systematic review on travel-related infections to estimate the TOSV incubation period. We estimated the incubation period at 12.1 days.

The initial detection of Toscana virus in phlebotomine sandflies from Turkey

Toscana virus (TOSV) is a prominent arthropod-borne viral agent of human central nervous system infections occurring in the Mediterranean region. The main transmission route to susceptible individuals involves sandflies as vectors. Despite several reports revealing widespread TOSV activity in Turkey, vectors remained unidentified. A sandfly field survey was carried out in five provinces in Central, Southeast and Mediterranean Anatolia in 2017 to identify TOSV and related sandfly-borne phleboviruses and Leishmania parasites, with evidence for circulation in the region. A total of 7136 sandfly specimens, collected via standard methods, were evaluated in 163 pools. TOSV was detected in 11 pools (6.7%), comprising Phlebotomus major sensu lato, Sergentomyia dentata and Phlebotomus papatasi species. TOSV partial L and S segment sequences were characterized, that phylogenetically clustered with local and global genotype A strains. An amino acid substitution outside the conserved motifs of the viral polymerase, also present in previous TOSV sequences in endemic regions, was observed. Leishmania tropica was detected in a single pool of Ph. sergentii (0.6%). This is the first report of TOSV in sandflies from Turkey, and this study further provides evidence for additional sandfly species with the potential to transmit TOSV.

Novel Toscana Virus Reverse Genetics System Establishes NSs as an Antagonist of Type I Interferon Responses

The sand fly-borne Toscana virus (TOSV) is the major cause of human meningoencephalitis in the Mediterranean basin during the summer season. In this work, we have developed a T7 RNA polymerase-driven reverse genetics system to recover infectious particles of a lineage B strain of TOSV. The viral protein pattern and growth properties of the rescued virus (rTOSV) were found to be similar to those of the corresponding wild-type (wt) virus. Using this system, we genetically engineered a TOSV mutant lacking expression of the non-structural protein NSs (rTOSVɸNSs). Unlike rTOSV and the wt virus, rTOSVɸNSs was unable to (i) suppress interferon (IFN)-b messenger RNA induction; and (ii) grow efficiently in cells producing IFN-b. Together, our results highlight the importance of NSs for TOSV in evading the IFN response and provide a comprehensive toolbox to investigate the TOSV life cycle in mammalian and insect host cells, including several novel polyclonal antibodies.

Sandfly-Borne Phlebovirus Isolations from Turkey: New Insight into the Sandfly fever Sicilian and Sandfly fever Naples Species

Southern Anatolia in Turkey at the border with Syria, where many refugee camps are settled, is endemic for sandfly-borne leishmaniasis. Sandfly-borne phleboviruses are also known to circulate in this region, although their relevance in terms of medical implications is virtually unknown. Therefore, the specific objectives of our study were firstly to identify isolate and characterise potentially pathogenic phleboviruses in sandflies; secondly to determine the complete genomic sequence of any viruses that we were able to isolate; and thirdly, to further our understanding of the potential medical importance and epidemiological significance of these viruses. To achieve these objectives, we organised field campaigns in 2012 and 2013. Two new phleboviruses (Toros and Zerdali viruses) were isolated and characterized by complete genome sequencing and phylogenetic analyses. Toros virus was genetically most closely related to Corfou virus within the Sandfly fever Sicilian group. Zerdali virus was most closely related to Tehran virus within the Sandfly fever Naples species. Although these new viruses belong to genetic groups that include several human pathogens, it is not yet clear if Toros and Zerdali viruses can infect humans and cause disease such as sandfly fever. Consequently, the availability of these genetically characterized infectious viruses will enable seroprevalence studies to establish their medical importance in this region and to assist the health agencies to develop appropriate and effective disease control strategies.

We provide evidence that sandfly-borne phleboviruses belonging to 3 distinct genetic and phylogenetic groups (Sandfly fever Naples virus [SFNV], Sandfly fever Sicilian virus [SFSV], and Salehabad virus [SALV]) co-circulate in Adana city, in Mediterranean Turkey. While Adana virus was recently described as a new member of the SALV species, Zerdali and Toros viruses are described here as new phleboviruses genetically closely related to SFNV and SFSV, respectively. In this study, isolated and characterised these two new viruses by determining their complete genome sequence and by phylogenetic analysis. This study demonstrates that 3 distinct viruses can co-circulate in the same geographic area and based on their phylogenetic relationships and association with sandflies are likely to be transmitted by these arthropod vectors. Our molecular and phylogenetic data are important for establishing group-specific molecular detection assays in order to further understand of the possible impact of these viruses in animal and human health in this region of Turkey.

Truncation of the C-terminal region of Toscana Virus NSs protein is critical for interferon-β antagonism and protein stability

Toscana Virus (TOSV) is a Phlebovirus responsible for central nervous system (CNS) injury in humans. The TOSV non-structural protein (NSs), which interacting with RIG-I leads to its degradation, was analysed in the C terminus fragment in order to identify its functional domains. To this aim, two C-terminal truncated NSs proteins, Δ1C-NSs (aa 1-284) and Δ2C-NSs (aa 1-287) were tested. Only Δ1C-NSs did not present any inhibitory effect on RIG-I and it showed a greater stability than the whole NSs protein. Moreover, the deletion of the TLQ aa sequence interposed between the two ΔC constructs caused a greater accumulation of the protein with a weak inhibitory effect on RIG-I, indicating some involvement of these amino acids in the NSs activity. Nevertheless, all the truncated proteins were still able to interact with RIG-I, suggesting that the domains responsible for RIG-I signaling and RIG-I interaction are mapped on different regions of the protein.

[Acute Toscana virus infection in an anti-HIV positive patient]

Sandfly fever is an infectious disease transmitted to people through sandfly bites. It usually takes three days and causes chills, high fever, headache, nausea-vomiting and myalgia. The causative agent, namely sandfly fever virus (SFV), is a member of the Bunyaviridae family, Phlebovirus genus. Toscana virus (TOSV) is a serotype of SFV, as so Sicilian and Naples viruses. Seroprevalence studies have demonstrated that SFV infections which have mild symptoms or asymptomatic, can be overcome. Studies concerning TOSV infections in Turkey are limited to a small number of regional seroprevalence surveys, blood-donor screening studies and detection of viral RNA in previously collected cerebrospinal fluid samples of suspected meningoencephalitis patients in whom no causative agents were identified. In this report from Turkey, the first acute case of TOSV infection diagnosed in a patient with HIV seropositivity, was presented. A 42-year-old male patient was admitted to Numune Research and Training Hospital Adana, Turkey with high fever, headache and malaise. The patient who lived in an area near to a forest in Istanbul, had no contact history with ticks, mosquitoes and other animals. He stated that he had had the symptoms before arriving to Adana. The patient was hospitalized due to leucopenia, anemia, and thrombocytopenia accompanying high fever. Serum samples were sent to National Arbovirus and Viral Zoonotic Diseases Unit of the Turkish Public Health Institute, for the detection of Crimean-Congo haemorrhagic fever (CCHF) virus and SFV. Western Blot test was run to confirm the presence of anti-HIV antibodies detected twice with ELISA. In the following days, the patient's fever and symptoms decreased, and thrombocyte levels increased. Although CCHF virus PCR and ELISA IgM tests as well as SFV IgM and IgG immunofluorescence antibody (IFA) tests were negative, real time reverse transcriptase PCR test yielded a positive result for TOSV. SFV IgG antibodies against Toscana and Naples viruses were found to be positive in the serum sample collected at the end of a three-week follow-up. Even though TOSV infection is usually known to have an asymptomatic clinical course, it may rarely lead to serious manifestations like meningoencephalitis. In our country where SFV is endemic, TOSV should be considered in the differential diagnosis of patients presenting with high fever and meningoencephalitis symptoms.

[Sandfly virus meningitis in a Danish traveller returning from Tuscany]

We report the first case of Sandfly virus meningitis in a Danish traveller returning from Tuscany. A 52 year-old man was admitted with headache, fever and photophobia. Spinal fluid showed evidence of aseptic meningitis. Indirect immuno-fluorescence assays showed presence of immunoglobulin (Ig)M and IgG antibodies reactive against Toscana virus, and Phlebovirus RNA was detected in blood by real-time polymerase chain reaction. The patient recovered spontaneously. Since Sandfly virus is a very common cause of meningitis in the Mediterranean countries, it is important to be aware of this disease in travellers returning from these areas.

Cocirculation of 2 genotypes of Toscana virus, southeastern France

Toscana virus (TOSV), an arthropodborne phlebovirus transmitted by sandflies, can cause febrile illness and meningitis. The vector of TOSV in France was unknown. We detected TOSV RNA in 2 (female Phlebotomus perniciosus) of 61 pools of sandflies captured in southeastern France. Two genotypes of TOSV were identified.

Reverse transcription, real-time PCR assay for detection of Toscana virus

BACKGROUND

The arthropod-borne Toscana virus is a common cause of acute neurological infection in the Mediterranean basin. Recently, a new lineage, highly divergent from the Italian prototype, has been reported in Spain.

OBJECTIVE

We describe a reverse transcription, real-time PCR assay for detection of both Toscana virus genotypes. The real-time PCR uses a TaqMan probe and an internal control to identify false negative results.

STUDY DESIGN

A conserved region of the two known lineages of Toscana virus, located at the 3' end of the small segment of their genomes, was chosen to design both the primers and the probe.

RESULTS

The sensitivity of the assay was 0.0158 TICD(50) per reaction of Toscana virus, equivalent to seven copies of cDNA. No other phleboviruses or RNA viruses were amplified by this specific real-time PCR.

CONCLUSIONS

The assay seems to be sensitive, reliable and easy to be applied in the diagnosis of autochthonous and/or imported suspected cases of Toscana virus infection.

Genetic variability of the M genome segment of clinical and environmental Toscana virus strains

Twenty-seven strains of Toscana virus, collected over a period of 23 years and isolated from several localities and from different hosts (humans, arthropods and a bat), were investigated by sequencing of a portion of the M genomic segment comprising the G(N) glycoprotein coding region. Sequence data indicated that the divergence among isolates ranged from 0 to 5.7 % at the nucleotide level and from 0 to 3.4 % at the amino acid level. Phylogenetic analysis revealed four main clusters. A close correspondence between viral strains and area/year of isolation could not be demonstrated, whilst co-circulation of different viral strains in the same area and in the same time period was observed for both patients and environmental viral isolates. Alignment of the deduced amino acid sequences and evolutionary analysis indicated that most of the sites along the gene may be invariable because of purifying and/or neutral selection.

A shared transcription termination signal on negative and ambisense RNA genome segments of Rift Valley fever, sandfly fever Sicilian, and Toscana viruses

The Phlebovirus genus (family Bunyaviridae) is composed of a diverse group of arboviruses that cause disease syndromes ranging from mild febrile illness to hemorrhagic fever with high fatality. Although antigenically similar, these viruses differ by approximately 25% at the genome level, and their ecologies, including geographic ranges, preferred vector species, and hosts, vary considerably. In contrast to other ambisense viruses, where RNA hairpin structures which serve as transcription termination signals are frequently found separating the opposite-sense open reading frames, no evidence of predicted high-energy hairpin structures was found at the ambisense junctions of phlebovirus S RNA segments. However, a conserved sequence motif was identified on both negative and ambisense genome segments that functions as a transcription termination signal for the N, NSs, and GPC mRNAs in three diverse phleboviruses, namely, Rift Valley fever, sandfly Sicilian, and Toscana viruses. The exact termination of nascent virus mRNA molecules was determined by 3' rapid amplification of cDNA ends. Surprisingly, analysis of the termini of mRNAs from both S and M segments of these three viruses revealed that transcription termination occurred immediately upstream of a conserved sequence motif with the general features 3'-C(1-3)GUCG/A-5'. In contrast, no corresponding sequence motif was found in the L segments, and analysis indicated a "runoff" transcript approach to L mRNA termination. The absolute requirement of the identified transcription termination motif was demonstrated by using a highly efficient Rift Valley fever virus reverse genetics system to generate live recombinant viruses with S segments lacking the termination signal motif for the NP or NSs mRNA and showing that these recombinant viruses generated mRNAs that failed to terminate correctly.

Toscana virus in Spain

Toscana virus (TOSV, Phlebovirus, family Bunyaviridae) infection is one of the most prevalent arboviruses in Spain. Within the objectives of a multidisciplinary network, a study on the epidemiology of TOSV was conducted in Granada, in southern Spain. The overall seroprevalence rate was 24.9%, significantly increasing with age. TOSV was detected in 3 of 103 sandfly pools by viral culture or reverse transcription-polymerase chain reaction from a region of the L gene. Nucleotide sequence homology was 99%-100% in TOSV from vectors and patients and 80%-81% compared to the Italian strain ISS Phl.3. Sequencing of the N gene of TOSV isolates from patients and vectors indicated 87%-88% and 100% homology at the nucleotide and amino acid levels, respectively, compared to the Italian strain. These findings demonstrate the circulation of at least 2 different lineages of TOSV in the Mediterranean basin, the Italian lineage and the Spanish lineage.

Emergence of Toscana virus in Europe

In southern Europe, Toscana virus is one of the three leading causes of aseptic meningitis.

Toscana virus (TOSV) is an arthropodborne virus first identified in 1971 from the sandfly Phlebotomus perniciosus in central Italy. Many case reports in travelers and clinical research and epidemiologic studies conducted around the Mediterranean region have shown that TOSV has a tropism for the central nervous system (CNS) and is a major cause of meningitis and encephalitis in countries in which it circulates. In central Italy, TOSV is the most frequent cause of meningitis from May to October, far exceeding enteroviruses. In other northern Mediterranean countries, TOSV is among the 3 most prevalent viruses associated with meningitis during the warm seasons. Therefore, TOSV must be considered an emerging pathogen. Here, we review the epidemiology of TOSV in Europe and determine questions that should be addressed in future studies. Despite increasing evidence of its major role in medicine as an emerging cause of CNS infections, TOSV remains an unstudied pathogen, and few physicians are aware of its potential to cause CNS infections.

Toscana virus central nervous system infections in southern Italy

Toscana virus was detected by reverse transcription-nested PCR in 5.6% of cerebrospinal fluid (CSF) samples from patients with meningitis and encephalitis during the summer in southern Italy. The central nervous system infections were associated with young adults and with a substantially benign clinical course. Presenting features and CSF findings are also discussed in the present report.

The N terminus of Rift Valley fever virus nucleoprotein is essential for dimerization

Rift Valley fever virus (RVFV) is a Phlebovirus in the Bunyaviridae family. The nucleoprotein N is the most abundant component of the virion; numerous copies of N associate with the viral RNA genome and form pseudohelicoidal ribonucleoproteins (RNPs) circularized by a panhandle structure formed by the base-paired RNA sequences at the 3' and 5' termini. These structures play a central role in transcription and replication. We investigated the intermolecular interactions of the RVFV N protein and found that after chemical cross-linking treatment, the nucleoprotein from purified RNPs migrates mainly as dimers. The N-N interaction was studied using the yeast two-hybrid system, the GST pull-down method, and mutational analysis. We demonstrated that the N terminus from residue 1 to 71, and particularly Tyr 4 and Phe 11, which are conserved among phlebovirus N sequences, are involved in the interaction. The C-terminal region did not seem to be essential for the N-N interaction. Moreover, we showed that N(TOS), the N protein of the related Toscana phlebovirus, interacts with itself and forms heterodimers with N(RVF), suggesting that the dimeric form of N may be a conserved feature in phlebovirus RNPs.

Unusual presentation of life-threatening Toscana virus meningoencephalitis

This case report describes a brother and a sister with severe meningoencephalitis caused by Toscana virus (TOSv). The clinical presentation was characterized by stiff neck, deep coma, maculopapular rash, diffuse lymphadenopathy, hepatosplenomegaly, renal involvement, tendency to bleeding, and diffuse intravascular coagulation. The boy had epididymo-orchitis. Recovery with neurologic sequelae as hydrocephalus was observed. Microbiological diagnosis was obtained by serological tests and reverse transcriptase-polymerase chain reaction. Sequencing of polymerase chain reaction products from the S and M segments was carried out. TOSv may be a causative agent in severe meningoencephalitis.

Detection and identification of Toscana and other phleboviruses by RT-nested-PCR assays with degenerated primers

Phleboviruses are a large and widespread group of viruses that are transmitted by arthropods. Toscana virus is one of the principal agents that causes meningitis in humans during the summer in Italy and, possibly, in other Mediterranean countries. Rift Valley Fever virus can cause serious illness in both animals and humans, leading to high morbidity and mortality, and is considered to be a potential agent for epizootics and human epidemics. Since information on this group of viruses is still scant, reliable laboratory tools for diagnosis and epidemiological surveillance must be developed, in order to ascertain their real impact on Public Health. Sequence data obtained from Spanish isolates of Toscana virus and other phleboviruses confirmed that natural genome variability may hamper the diagnosis of these agents by molecular methods, so this must be borne in mind when developing reliable assays. In view of the above, a novel and useful protocol has been developed for the detection and specific identification of every member of the phlebovirus genus present in a sample, including Toscana virus, based on a generic RT-nested-PCR, followed by sequencing of the amplified fragment. A change in this method also allowed specific direct detection and identification of wild isolates of Toscana virus of different geographical origin, using newly designed primers. Testing clinical samples with these assays confirmed the role of Toscana virus as an agent that causes acute aseptic meningitis in the central region of Spain.

Human antibody response to Toscana virus glycoproteins expressed by recombinant baculovirus

The arthropod-borne Toscana virus has been associated with acute neurological disease in humans. In this study, the viral envelope glycoproteins were expressed in soluble form in a baculovirus system. The recombinant sGN and sGC proteins were used as viral antigens in a Western blot assay to analyze the specific immune response in sera from patients with recognized virus-associated aseptic meningitis. The anti-glycoprotein and the anti-nucleoprotein N IgG responses were compared by an immunoassay based on the recombinant proteins. In this system, all the sera showed a high reactivity to the N protein, but they differed in the response to the glycoproteins.

Fast duplex one-step RT-PCR for rapid differential diagnosis of entero- or toscana virus meningitis

Acute meningitis is the most common neurologic disease that involves the central nervous system. The spectrum of infectious agents that cause neurologic infection is remarkably broad and numerous viruses are the most frequent cause of the aseptic meningitis syndrome. We applied a multiplex one-step method for the rapid detection of the genomic RNA of different neurotropic viruses: particles in the genus Enterovirus and Toscana virus, which are the most representative aetiologic agents in our country during the spring-summer period. We have evaluated the sensitivity and the specificity of the multiplex one-step test on positive controls and on RNA extracted from clinical samples harvested from 475 patients with meningitis hospitalized during the 1996-2001 period. The multiplex one-step RT-nPCR protocol allows for the detection of enterovirus and Toscana virus RNA in a single sample, by using, at the same time, a very small clinical sample volume. In our study we were able to diagnose 192 cases of meningitis by Toscana virus and 31 cases by enteroviruses out of 475 cases of meningitis utilizing the described one-step multiplex method.