Laboratory diagnosis of Toscana virus infection by enzyme immunoassay with recombinant viral nucleoprotein

Identification of a Neutralizing Epitope on TOSV Gn Glycoprotein

Emerging and re-emerging viral infections have been an important public health problem in recent years. We focused our attention on Toscana virus (TOSV), an emergent neurotropic negative-strand RNA virus of the Phenuiviridae family. The mechanisms of protection against phlebovirus natural infection are not known; however, it is supposed that a virus-neutralizing antibody response against viral glycoproteins would be useful to block the first stages of infection. By using an improved memory B cell immortalization method, we obtained a panel of human mAbs which reacted with TOSV antigens. We identified three epitopes of TOSV Gn glycoproteins by neutralizing mAbs using synthetic peptide arrays on membrane support (SPOT synthesis). These epitopes, separated in primary structure, might be exposed near one another as a conformational epitope in their native structure. In vivo studies were conducted to evaluate the humoral response elicited in mice immunized with the identified peptides. The results underlined the hypothesis that the first two peptides located in the NH₂ terminus could form a conformational epitope, while the third, located near the transmembrane sequence in the carboxyl terminus, was necessary to strengthen neutralizing activity. Our results emphasize the importance of identifying neutralizing epitopes shared among the various phleboviruses, which could be exploited for the development of a potential epitope-based diagnostic assay or a polyvalent protective vaccine against different phleboviruses.

Epidemiology of Toscana virus in South Tuscany over the years 2011-2019

BACKGROUND

Toscana virus (TOSV) is a Phlebovirus transmitted to humans by phlebotomines and represent an etiological agent of acute aseptic meningitis (AAM) in countries where the virus is endemic, including Italy. Incidence of TOSV infections is closely associated with the geographical distribution of the phlebotomine vectors which in turn is affected by climate changes that determine survival and spread. As a result, TOSV infections show a seasonal trend with a peak of incidence in summer months.

OBJECTIVES

To measure the prevalence of TOSV infections in AAM patients in central Italy and evaluate the climate changes in phlebotomine vectors ecology and virus propagation.

STUDY DESIGN

One thousand and seventy-three cerebrospinal fluid samples (CSFs), collected from patients with suspected viral meningitis, were collected over nine years (2011-2019) during the May to October period and tested for viruses most commonly associated with AAM. Serum samples addressed to the Microbiology and Virology Unit of "S. Maria delle Scotte" Hospital for confirmation acute TOSV infection (n = 324) were tested for TOSV-specific IgM and IgG.

RESULTS

Among the CSF samples, 1.3% were positive for Enteroviruses; 0.9% for Varicella zoster virus, 1.9% for Herpes simplex virus type-1/2 and 4.6% for TOSV. Serum IgM analyses disclosed TOSV-specific IgM in 27.1% of sera suggesting the predominant involvement of TOSV in neuroinvasive infections.

CONCLUSIONS

This data confirms the predominant role of TOSV as causative agent of AAM during the summer time in endemic countries. Moreover, climate changes affecting phlebotomine vectors persistence, reproduction and activity could be involved in the cyclic nature of TOSV infection reported during the last nine years.

Seroprevalence study of Toscana virus and viruses belonging to the Sandfly fever Naples antigenic complex in central and southern Italy

Sandfly fever viruses are transmitted by the bite of phlebotomine sandflies; serotypes sandfly fever Naples virus, sandfly fever Sicilian virus and sandfly fever Cyprus virus cause febrile illness, whereas Toscana virus (TOSV) may cause neuroinvasive infections. Although TOSV is an important cause of aseptic meningitis in central and southern Italy, in many cases the infection is asymptomatic, leading to underestimation of the actual spread of the virus. This serosurvey aimed to assess the seroprevalence of TOSV in a random population in Siena (Tuscany, central Italy) in 2003-2004 and 2013-2014 and Bari (Apulia, southern Italy) in 2004 and 2015. 2132 serum samples were tested for the presence of anti-TOSV/SFNV IgG by means of ELISA and IFA commercial tests. Seroprevalence rates were compared in the two cities and over a ten-year period in the same city. Seroprevalence results in the Siena population (22.95% in 2003-2004 vs 26.75% in 2013-2014) confirmed the endemic circulation of TOSV and closely related viruses in central Italy, without major changes over the last decade, while no significant prevalence was observed in Bari (2.90% in 2004 vs 1.85% in 2015).

Comparison of a new prototype immunochromatographic assay and a commercial enzyme-linked immunosorbent assay for the detection of serum antibodies against Toscana virus

Toscana virus (TOSV) is an arthropod-borne virus, transmitted to humans by Phlebotomus spp. Sandflies, which causes neurological diseases such as aseptic meningitis and meningoencephalitis. The commercial enzyme-linked immunosorbent assay (ELISA) is used widely to detect anti-TOSV IgG and IgM antibodies and to allow for rapid diagnosis of infection (Diesse Diagnostica Senese, Siena, Italy). Recently, an immunochromatographic assay (ICA) was developed for human anti-TOSV IgG or IgM detection by InBios International (Seattle, WA, USA). A comparison of the two diagnostic assays was performed on one hundred serum samples collected from patients hospitalized with suspected TOSV meningitis. Both assays were in excellent agreement, for both IgG and IgM detection. For IgM, 64/65 ELISA positive samples were positive by ICA. One serum, positive for specific IgM by ELISA but negative by ICA, was confirmed by direct diagnosis, with TOSV RNA detection in the patient's cerebrospinal fluid by PCR. For IgG, 64 samples were positive by ICA out of 71 ELISA positive samples. The discordant sera were positive by immunofluorescence and neutralization tests. Three out of these seven samples were also positive by IgM ICA. The sensitivity of these new assays compared to ELISA, which is used routinely, was 98.5% for IgM and 90.1% for IgG, while specificity was 100% in both cases. This data shows that ICA could be a reliable alternative test for serological diagnosis of TOSV infection in humans.

Diagnostic tools for Toscana virus infection

Toscana virus (TOSV; Phlebovirus, Bunyaviridae) is an important etiological agent of acute meningitis and meningoencephalitis in Mediterranean countries. Laboratory diagnosis has been carried out in serological studies using ELISA, immunofluorescence and/or neutralization tests that are not influenced by the virus viability; however, in the acute phase of the infection, nucleic acid amplification techniques are the methods of choice to diagnose viral meningitis from cerebrospinal fluid samples. Molecular methods are rapid and sensitive and, unlike traditional methods, such as virus isolation by cell culture, they are not influenced by the viability of the virus in the clinical specimen; however, the RNA integrity is crucial for the success of these methods. Real-time PCR is the most important molecular method used in laboratories worldwide, since it is less time-consuming and it reduces the risk of contamination. Therefore, a sensitive real-time PCR has been developed for diagnosis of suspected cases of TOSV infection either autochthonous and/or imported, since a new lineage of TOSV, divergent from the Italian prototype, has recently been reported in Spain.

Serological evidence of Toscana virus infection in Portuguese patients

Toscana virus (TOSV) is an emerging Phlebovirus of growing interest as a human pathogen in the Mediterranean Basin. In Portugal, however, little is known about the prevalence of TOSV infection. The aim of this work was to perform a seroprevalence study in patients with requests for laboratory diagnosis of vector-borne viruses. A total of 538 patients with and without neurological signs from 2004 to 2008 were studied by in-house indirect immunofluorescence assay and commercial enzyme-linked immunosorbent assays. A prevalence of 4.2% for IgG antibodies was found in the group of patients with neurological signs. Five (3%) of these had recent infections. In the group with no neurological signs, the IgG prevalence was 1.3%. Two samples, belonging to two patients, were also confirmed with plaque reduction neutralization tests with the TOSV ISS. Phl.3 Italian strain. This work showed that TOSV is present and causing disease from north to south in Portugal. The probable circulation of different phlebovirus serotypes in Portugal emphasizes the need for further studies.

Performance of various commercial assays for the detection of Toscana virus antibodies

INTRODUCTION

Sandfly fever virus (SFV) serotypes sandfly fever Naples virus, sandfly fever Sicilian virus, and sandfly fever Cyprus virus cause febrile diseases, whereas Toscana virus (TOSV) is responsible for aseptic meningoencephalitis. Diagnosis and surveillance of TOSV depend heavily on virus serology, and various commercial assays utilizing various antigen sources and formats have been available. The aim of this study was to perform comparative evaluation of commercially available serological assays for anti-TOSV immunoglobulins.

MATERIALS AND METHODS

A collection of 120 sera from healthy blood donors from an endemic region, previously identified to be reactive for antibodies against various SFV serotypes by indirect immunofluorescence test (IIFT), was reevaluated for IgG/IgM via IIFT, enzyme-linked immunosorbent assay, and an immunoblot assay manufactured by Euroimmun, Diesse, and Mikrogen, respectively. Virus neutralization test (VNT) was performed for 99 sera using standard TOSV, sandfly fever Sicilian virus, and sandfly fever Naples virus strains.

RESULTS

A total of 89 samples (74.2%) were reactive for TOSV IgG in at least one of the commercial assays, and 31 samples (31.3%) were reactive in VNT for various SFV serotypes. Average percentage agreements among commercial assays and between VNT and the commercial assays were noted as 57.8% and 62.6%, respectively. No significant correlation between assay results and VNT titers was observed. SFV IgM antibodies were detected in a total of eight samples (6.7%) via IIFT, which were nonreactive in enzyme-linked immunosorbent assay and VNT.

DISCUSSION

Commercial diagnostic immunoassays displayed slight to fair agreement for TOSV IgG as assessed via kappa and percentage agreement values. The results could only be confirmed via virus neutralization in a portion of the samples, and overall agreement between the commercial assays and VNT was slight. Commercial assays such as immunoblot can be used in addition to VNT for confirmation of TOSV exposure.

Age-dependent seroprevalence of Toscana virus in central Italy and correlation with the clinical profile

In order to estimate the antibody prevalence rates for Toscana virus (TOSV) among children and adults, we evaluated the seroprevalence of TOSV in a population (n = 2,737) living in Tuscany during the period of 1999 to 2006. The seroprevalence rate was 19.8% in adults and 5.8% in children, showing an age-dependent increase in TOSV-specific immunity. Meningitis due to TOSV infection was more frequent in adults than in children.

Chemotherapeutic drugs may be used to enhance the killing efficacy of human tumor antigen peptide-specific CTLs

The effects of anticancer chemotherapy on antigen-specific cytotoxic T lymphocytes (CTLs) are mostly unknown. We tested the effects of cytotoxic drugs such as 5-fluorouracil, gemcitabine, and oxaliplatin on the functional activity of antigen-specific CTL cultures derived from the peripheral blood mononuclear cells of human donors. We found that a biweekly drug-exposure of human HLA-A(*)02.01+ CTLs derived from bulk cultures led to completely different effects if occurring early (day second) or late (day thirteenth) after the in vitro stimulations with the cognate peptides. In the first case, there was a significant CTL inhibition, whereas in the second, there was a marked enhancement of the antigen-specific cytolytic activity. Results of immunocytofluorimetric studies and CTL/natural killer inhibition assays suggested that the latter effect could be related to a more selective drug-mediated inhibition of cohabitant T regulatory (reg) cells. These results were translated in an in vivo therapeutic mouse model where humanized HLA-A(*)02.01 transgenic mice inoculated with EL-4/humanized HLA-A(*)02.01 transgenic mice showed a prolonged survival and the greatest rate of cure when receiving a combined treatment with a thymidylate synthase-specific peptide vaccine and a multidrug chemotherapy regimen administered late after immunization. Tumor samples derived from this group of mice showed a reduced expression of the target thymidylate synthase antigen, a marked reduction of T(reg)s, and a noteworthy infiltration of C8+ T cells. These results may have clinical implications for the design of new translational anticancer regimens aimed at combining chemotherapy and immunotherapy.

Immunization with Toscana virus N-Gc proteins protects mice against virus challenge

Toscana virus (TOSV) is an emerging virus, circulating in the Mediterranean area, that is responsible for aseptic meningitis, meningoencephalitis, and encephalitis. The development of a vaccine that could provide complete protection from TOSV infection is needed. In this study we investigated the capacity of TOSV structural proteins, nucleocapsid protein N and the two Gc and Gn glycoproteins, produced as recombinant proteins, in an animal model. In particular, we investigated their role in inducing specific and protective immune responses against virus infection. Mice were immunized intraperitoneally using TOSV antigens singly or in combination. The results show that only the N-Gc combination was able to protect 100% of animals from a lethal challenge with a neurovirulent strain of TOSV. This potential vaccine induces high serum antibody titres with neutralizing activity and it is safe for animals. Moreover, immunization induces a virus specific cell-mediated immune response, in particular a CD8+ T cell response associated with a marked expression of interferon gamma. These results indicate that the N+Gc viral antigen combination could be useful for future development of a vaccine controlling the spread of this emerging virus that could pose a new threat for humans.

Preparation and evaluation of a recombinant Rift Valley fever virus N protein for the detection of IgG and IgM antibodies in humans and animals by indirect ELISA

This paper describes the cloning, sequencing and bacterial expression of the N protein of the Rift Valley fever virus (RVFV) ZIM688/78 isolate and its evaluation in indirect ELISAs (I-ELISA) for the detection of IgM and IgG antibodies in human and sheep sera. Sera used for the evaluation were from 106 laboratory workers immunised with an inactivated RVF vaccine, 16 RVF patients, 168 serial bleeds from 8 sheep experimentally infected with wild type RVFV and 210 serial bleeds from 10 sheep vaccinated with the live attenuated Smithburn RVFV strain. All human and animal sera that tested positive in the virus neutralisation test were also positive in the IgG I-ELISA. There was a high correlation (R2=0.8571) between virus neutralising titres and IgG I-ELISA readings in human vaccinees. In experimentally infected sheep IgG antibodies were detected from day 4 to 5 post-infection onwards and IgM antibodies from day 3 to 4. The IgG I-ELISA was more sensitive than virus neutralisation and haemagglutination-inhibition tests in detecting the early immune response in experimentally infected sheep. The I-ELISAs demonstrated that the IgG and IgM response to the Smithburn vaccine strain was slower and the levels of antibodies induced markedly lower than to wild type RVFV infection.

Infecciones por el virus de Toscana, el virus del Nilo occidental y otros arbovirus de interés en Europa

Arbovirosis, viral infection transmitted by arthropods, is a widespread health problem. Recurrent outbreaks caused by some of these viruses such as dengue or West Nile strains in regions where they do not appear frequently, justify the establishment of global control measures. Tick-borne encephalitis viruses, sand fly fever viruses (Toscana, Naples and Sicily) and occasionally West Nile and Crimean-Congo fever viruses are the most frequent causes of arbovirosis in Europe, although circulation of other potentially pathogenetic viruses such as Chikungunya has also been detected. The only native arbovirosis described in Spain is infection produced by Toscana virus, which causes aseptic, usually benign meningitis. Nevertheless, some West Nile virus-associated meningo-encephalitis cases have been described in France, Portugal and countries in the Magreb region, increasing the risk of sporadic occurrence of these processes in our country. To achieve an accurate diagnosis, high clinical suspicion is required as well as highly specific laboratory techniques, mainly based on IgM detection, RT-PCR and viral culture of CSF and/or serum.

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.

A Mediterranean arbovirus: the Toscana virus

Toscana virus (Bunyaviridae family, Phlebovirus genus) is a sandfly fever virus responsible for human neurological infections. Sandfly viruses are transmitted by insect vectors (Phlebotomus species) and the infection is present in climatic areas that allow the life cycle of the vector. The arthropode-borne Toscana virus is the etiologic agent of meningitis, meningoencephalitis, and encephalitis. The frequency of this neuropathic infection increases in the summer months, peaking in August in the endemic Mediterranean areas (Italy, Portugal, Spain, and Cyprus). Infection diagnosis is carried out by molecular assays and immunoenzymatic tests, which are rapid and sensitive. Recent studies have investigated the antigenic properties of the viral proteins (nucleoprotein N and surface glycoproteins G1 and G2), to better understand their immunogentic role.

Epidemiological, clinical and laboratory aspects of sandfly fever

PURPOSE OF REVIEW

Sandfly fever viruses are still a significant health problem in many regions of the world, such as Africa, the Mediterranean basin, the Middle East, and Central Asia. This review provides an update on the advances in knowledge about epidemiological, clinical, and laboratory aspects of infections caused by Toscana, Sicilian and Naples viruses.

RECENT FINDINGS

Diagnosis of Toscana virus infection has been facilitated by new molecular methods and by immunoenzymatic tests based on the recombinant nucleoprotein. Gene analysis has allowed identification of circulating Toscana variants possibly involved in the protean pathomorphism and extreme variability of the clinical picture. New attention has been addressed to the antigenic properties of the viral proteins (the nucleoprotein N and the surface glycoproteins G1 and G2), in order to understand their immunogenetic role. High genetic divergence within the serocomplexes belonging to each of the Sicilian and the Naples viruses has suggested that infection with one genotype may not completely immunize against infection with all other genotypes in a given serocomplex. These findings could serve as a basis for vaccine development and may account for reports of multiple episodes of sandfly fever in the same host. Recently, the performance of analysis models based on weather data and reported vector surveys has allowed the prediction of the risk of acquiring sandfly infection in the endemic geographic areas.

SUMMARY

Recent developments include a better knowledge of the epidemiological, clinical, and laboratory aspects of sandfly infection, while the search for effective drugs and vaccines is still in progress.

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.

Serological survey of Toscana virus infections in a high-risk population in Italy

Toscana virus is the most important agent responsible for meningitis in central Italy. We report a serosurveillance study, using an immunoenzymatic assay, of 360 serum samples harvested from a high-risk population occupationally exposed to Toscana virus in two regions of Italy, Tuscany and Piedmont. The results indicates a seroprevalence of Toscana virus of 77.2% in the forestry workers, particularly in the Tuscany region. This fact is strictly correlated with the ecological niches specific for the survival of Toscana virus arthropod vector.

Acute meningitis due to Toscana virus infection among patients from both the Spanish Mediterranean region and the region of Madrid

Toscana virus (TOSV) is a member of the genus Phlebovirus that is transmitted to humans by two different species of sand fly and causes acute aseptic meningitis (AAM) and meningoencephalitis in Central Italy. Fifteen cases of AAM due to TOSV have been found at the Spanish province of Granada, but no data regarding the presence of TOSV-related disease in other regions of Spain have been still reported. A collection of 88 serum and 53 cerebrospinal fluid (CSF) samples taken from 81 selected patients with AAM of unknown aetiology, residing at Madrid or at the southern Mediterranean coast of Spain, was retrospectively studied for presence of TOSV-specific antibodies from both IgG and IgM classes. Anti-TOSV IgG was also investigated in 457 serum samples from healthy individuals, aged 2-60 years, residing at the south of the Region of Madrid. Specific IgM in serum and/or intrathecally produced anti-TOSV IgG were detected in seven patients, three residents from the Mediterranean region and the remainder four from the Region of Madrid. The overall prevalence of anti-TOSV among the healthy population studied was 5%. These results confirm the role of TOSV as an agent causing AAM in the Spanish Mediterranean coast, extend these findings to the central region of the country and suggest that TOSV might be producing infection and neurological disease in every area of Spain harbouring significant populations of the viral vectors.

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.

Encephalitis without meningitis due to sandfly fever virus serotype toscana

The role of Toscana (TOS) virus in producing encephalitis without meningitis is uncertain. We studied 2 cases of TOS virus encephalitis without meningitis by means of nested polymerase chain reaction assay and DNA sequencing. Findings confirm that TOS virus may directly cause encephalitis and suggest the usefulness of DNA sequencing in investigating relationships between TOS virus molecular patterns and the spectrum of neurological involvement.