Nested RT-PCR for detection of sandfly fever virus, serotype Toscana, in clinical specimens, with confirmation by nucleotide sequence analysis

Evidence of feline panleukopenia infection in cats in India

The samples collected from cats showing clinical signs suspected for feline panleukopenia infection were confirmed using various molecular techniques and virus isolation. The suspected samples were confirmed using feline parvovirus specific primers. The partial VP2 gene was submitted to GenBank for the first time in India (Accession number JQ684660.1). The PCR positive samples were further amplified using full length FPV VP2 gene specific primers and sequenced. The blast analysis revealed that the local field isolates of FPV showed 99 % homology with other FPV sequences available in the GenBank. The evidence for occurrence of feline panleukopenia infection in cats in Tamil Nadu, India was further confirmed by host specific nucleotides present in the VP2 gene region as well as virus isolation in A72 cell line.

Emergence of Toscana virus in the mediterranean area

Toscana virus (TOSV) is an arthropod-borne virus, identified in 1971, from Phlebotomus perniciosus and Phlebotomus perfiliewi in central Italy. TOSV belongs to the Phlebovirus genus within the Bunyaviridae family. As other bunyaviruses, the genome of TOSV consists of 3 segments (S for small, M for Medium, and L for Large) respectively encoding non structural and capsid proteins, envelope structural proteins, and the viral RNA-dependant RNA-polymerase. It is transmitted by sand flies. Therefore its distribution is dictated by that of the arthropod vectors, and virus circulation peaks during summertime when sandfly populations are active. Here, we reviewed the epidemiology of TOSV in the old world. First evidence of its pathogenicity for humans, specifically its propensity to cause central nervous system (CNS) infections such as meningitis and encephalitis, was reported in central Italy. After 2000, it was recognized that TOSV had a much larger geographic distribution than initially believed, and was present in most of the Western European countries located on the northern border of the Mediterranean Sea (Portugal, Spain, France, Greece, Croatia) as well as eastern countries such as Cyprus and Turkey. In the countries where TOSV is present, it is among the three most prevalent viruses in meningitis during the warm seasons, together with enteroviruses and herpesviruses. Up to now, epidemiological data concerning Northern Africa and other countries located south of the Mediterranean are scarce. TOSV must be considered an emerging pathogen. Despite the important role played by TOSV in CNS infections, it remains a neglected agent and is rarely considered by physicians in diagnostic algorithms of CNS infections and febrile illness during the warm season, probably because of the lack of information.

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.

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.

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.

Acute meningitis owing to phlebotomus fever Toscana virus imported to France

Acute lymphocytic meningitis, seen in France in summer, is often due to enteroviruses. Arboviruses as West Nile and tick-borne encephalitis do exist in Europe, but other viruses are rarely considered in patients unless they have had recent tropical travel. Toscana virus infection, which is endemic, especially in Italy,1-3 has been documented in some European travelers returning from Italy,4-6 but surprisingly was not documented in France until recently.7 We report a case of meningitis caused by Toscana virus imported to France.

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.

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.

Sequence analysis of Malaysian infectious bursal disease virus isolate and the use of reverse transcriptase nested polymerase chain reaction enzyme-linked immunosorbent assay for the detection of VP2 hypervariable region

The VP2 hypervariable region of P97/302 local infectious bursal disease virus (IBDV) isolate was amplified by the reverse transcriptase (RT) nested polymerase chain reaction (PCR) and cloned. This region of P97/302 local isolate was sequenced and compared with eight other reported IBDV sequences. The result showed that P97/302 IBDV was most identical to the reported very virulent IBDV strains because it has amino acid substitutions at positions 222, 256, 294, and 299, which encode alanine, isoleucine, isoleucine, and serine, respectively. This region can be digested with restriction enzymes of Taq1, Sty1, Ssp1 but not with Sac1. The P97/302 isolate was then used for the optimization of RT nested PCR enzyme-linked immunosorbent assay (ELISA). The RT nested PCR ELISA was able to detect 10(-4) dilution of the infected bursa homogenates and was 10 times more sensitive when compared with the agarose gel detection method. The RT nested PCR ELISA can detect up to 0.48 ng of the PCR product. The specificity of this nested PCR ELISA was also high (100%).

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.

Closed one-tube reverse transcription nested polymerase chain reaction for the detection of pestiviral RNA with fluorescent probes

An assay was developed in which reverse transcription (RT), nested polymerase chain reaction (PCR) and accumulation of amplicon-specific fluorescence could take place in a single, closed reaction tube. The assay, which was classical swine fever virus RNA-specific, was compared with other methods for detection of this virus, including various RT-PCR configurations, virus isolation and ELISA. The new method was very sensitive, and less prone to giving false positive results compared to nested PCR carried out in separate reaction tubes. Substitution of different fluorescent probes resulted in specific tests for border disease virus and for bovine viral diarrhoea type II (BVD-II), and one that could detect all pestiviruses except for some BVD-II viruses.

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

A recombinant enzyme immunoassay (rEIA) to detect serum immunoglobulin M (IgM) and IgG to Toscana virus (TOSV) was developed with the aim of establishing a simple and easily available assay for diagnosing acute and/or previous infections. The rEIA, based on the recombinant nucleoprotein of TOSV expressed in Escherichia coli, was evaluated with 97 serum samples collected in an area where TOSV is endemic and compared to an analogous assay based on cell-derived TOSV. Discordant results were resolved by immunoblotting (IB). Twenty-two of these samples, obtained from subjects hospitalized during the summer season with meningitis of suspected TOSV etiology, were further characterized by indirect immunofluorescence and IB, and detection of specific TOSV RNA sequences in the cerebrospinal fluid of these patients was attempted by nested PCR. The results indicated that rEIA was able to diagnose acute TOSV infection by detection of specific serum IgM in all of the subjects with TOSV meningitis confirmed by nested PCR or serology. The overall sensitivity and specificity of rEIA were both 100% for IgM detection and 100 and 96.6%, respectively, for IgG detection. Thus, rEIA appears to be a simple and reliable laboratory test for the diagnosis of acute TOSV infection and for the assessment of immune status.

A recombinant Toscana virus nucleoprotein in a diagnostic immunoblot test system

Sandfly fever, a vector-borne disease endemic in the Mediterranean region, is caused by Toscana virus (TOS). The disease is increasingly important as a travel-related infection. Serological diagnosis is currently dependent on viral antigens derived from TOS-infected cell cultures. In this study, we report the cloning and expression of the TOS nucleoprotein (N) in Escherichia coli and evaluation of the recombinant (r) TOS N protein as an antigen for immunoblot assays. The TOS N gene was amplified by reverse-transcriptase polymerase chain reaction and cloned into the bacterial expression vector pTrcHis-A. Sera with known TOS antibody status were used to evaluate the immunoblot assay. The expressed rTOS N protein was purified and used as antigen for immunoblots. By recombinant immunoblot, the TOS antibody status (IgM and/or IgG) of the test panel was correctly identified. No cross-reactivity was detected. The rTOS N protein is useful as an antigen for immunoblot assays, and will enable more laboratories to perform TOS antibody diagnosis.

Diagnostic potential of Toscana virus N protein expressed in Escherichia coli

The nucleocapsid (N) protein of the Toscana (TOS) virus was expressed in Escherichia coli by using a pET15b vector. The recombinant protein was purified by affinity chromatography and was characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, immunoblotting, and enzyme immunoassay (EIA). The recombinant antigen was reactive with positive human sera, and the reactivity correlated very well (r = 0.9) with that of a whole-virus antigen when tested by EIA with 30 TOS virus-positive and 30 TOS virus-negative serum samples. The results demonstrate that the recombinant N protein can be easily produced in a procaryotic system and used for diagnostic assays for TOS virus immunity.

Evidence of Toscana virus variants circulating in Tuscany, Italy, during the summers of 1995 to 1997

The Toscana virus can cause neurological infection in adults. This study of 112 cases of acute meningitis which occurred during the summers of 1995, 1996, and 1997 demonstrated the presence of viral RNA in the cerebrospinal fluid of 56 patients. Their sequence analysis shows four variants of the Toscana virus.

Universal diagnostic RT-PCR protocol for arboviruses

A selected number of PCR protocols were evaluated to determine if they could serve as a universal protocol for detecting and identifying all arboviruses. In this study, four parameters that affect the efficacy of RT-PCR (RNA extraction method, choice of reverse transcriptase, choice of DNA polymerase and thermocycling program) were evaluated in combination. The most optimal combination of those parameters employed use of silica gel membrane spin column, RAV-2 reverse transcriptase, Tth DNA polymerase, and a simple modification of a published thermocycling program. By this modified protocol, viral RNA could be amplified satisfactorily with more than 50 pairs of primers designed for diagnosis of arboviruses representing five families. The sensitivity and specificity obtained by this universal protocol were comparable to those obtained by the original protocol for each primer pair tested; and for some primers, improved sensitivity was observed. It was also found that a simple modification of a suggested protocol of a commercial RT-PCR kit could produce nearly identical results and serve as another universal protocol. With the use of a universal diagnostic reverse transcriptase-polymerase chain reaction (RT-PCR) protocol, simultaneous screening of clinical or biological specimens against a large number of RNA viruses belonging to many families can be performed more efficiently for etiologic determination in the situations complicated by the difficulty of differential diagnosis. Furthermore, such a universal protocol facilitates reducing the cost of PCR-based diagnostic operation and standardizing the qualities of PCR-based diagnosis within an institution or among collaborating institutions. A logical strategy is to conduct diagnosis in two stages by using broadly group-reactive primers in the first stage to narrow the range of possible etiologic agents and using virus-specific primers in the second stage for identification. Before such a strategy is employed, however, more group-reactive primers for a large number of arboviruses, for which no such primers currently exist, must be made available. Furthermore, the best pair or pairs of primers need to be selected for each virus for the second stage of the strategy.

Immunoblot detection of antibodies to Toscana virus

Sera from patients with sandfly fever caused by Toscana virus (TOSV) infection were tested by immunoblot for specific antibody response to TOSV derived from infected Vero-E6 cells. The 28 kDa TOSV nucleoprotein (N) was identified as the major immunodominant protein recognized by immunoblot. In sera of patients with acute TOSV infection, specific antibodies of the IgM, IgA, and IgG class were detected. Using sandfly fever virus, serotypes Sicilian (SFSV) and Naples (SFNV), as antigens for immunoblot, TOSV antibody-positive sera cross-reacted with the corresponding N proteins. These sera reacted for IgM and IgG by SFSV immunoblot, and for IgM by SFNV immunoblot. The diagnosis of sandfly fever may be confirmed by TOSV immunoblot.