Incubation Period for Neuroinvasive Toscana Virus Infections

Toscana virus: A comprehensive review of 1381 cases showing an emerging threat in the Mediterranean regions

BACKGROUND

Toscana virus (TOSV) is a sand fly-borne phlebovirus causing central nervous system (CNS) infection in Mediterranean countries, during summer season. However, clinical aspects of the disease caused by this virus are poorly known by clinicians, so that its prevalence is probably underestimated due to a lack of diagnosis.

STUDY DESIGN

The data was gathered from all available case series and retrospective studies identifying TOSV as the causative viral agent. The informations of age, sex, clinical characteristics, laboratory findings, imaging results and clinical outcomes of TOSV infection were recorded and analyzed.

RESULTS

A total of 95 articles including TOSV infections resulting in a total of 1381 cases, were analyzed. Our findings indicate that TOSV affects individuals across various age groups, with a median age of 44.45 years. A notable disparity in infection rates between genders, with men being significantly more likely to present symptoms due to TOSV than women, with a sex ratio of 2.0. The clinical presentation of TOSV infection encompasses a range of symptoms, including fever, headache, retro-orbital pain, neurological and muscular manifestations with less common reports of cutaneous and gastrointestinal symptoms. To date, six fatalities have been attributed to TOSV infections, with a median age of 76 years. Diagnostic evaluation of TOSV infections often involves the analysis of cerebrospinal fluid, where findings may include an elevated white blood cell count.

CONCLUSIONS

These findings underscore the diverse clinical manifestations of TOSV infections including flu like symtomps. TOSV is an emerging infectious threat that warrants inclusion in the diagnostic protocols for patients presenting with CNS, particularly within the Mediterranean basin or for those with recent travel history to endemic regions during warmer months when sand flies are actively circulating.

Human neuroinvasive Toscana virus infections in Italy from 2016 to 2023: Increased incidence in 2022 and 2023

BackgroundToscana virus (TOSV) is transmitted to humans through bites of infected sand flies. Neuroinvasive TOSV infections are leading causes of meningitis/encephalitis in southern Europe and notifiable in Italy since 2016. In 2022-23, Italy experienced extreme climate anomalies and a concomitant increase in mosquito and tick-borne disease transmission.AimTo identify the spatiotemporal distribution and risk groups of neuroinvasive TOSV infections in Italy in 2022-23 vs 2016-21.MethodsWe retrospectively described all autochthonous, laboratory-confirmed neuroinvasive TOSV cases notified to the national surveillance system in 2016-23 using frequencies, proportions, incidences and incidence risk ratios (IRRs) with 95% CIs, stratified by year, sex, age, region/autonomous province (AP) of infection/exposure and infection/exposure municipality by urbanisation level.ResultsIn 2022-23, 276 cases were notified (average annual incidence: 2.34/1,000,000 population) vs 331 cases in 2016-21 (0.92/1,000,000), with increased incidence extending into September. In 2022-23, infections were acquired in 12/21 regions/APs, predominantly in Emilia Romagna (57.6%; 159/276) as in 2016-21, including four regions/APs with no local infections in 2016-21. Similar to 2016-21, during 2022-23 residence in rural municipalities (vs urban), male sex, working age (19-67 years) and age > 67 years (vs ≤ 18 years) were identified as risk factors with IRRs of 2.89 (95% CI: 2.01-4.17), 2.17 (95% CI: 1.66-2.84), 5.31 (95% CI: 2.81-10.0) and 5.06 (95% CI: 2.59-9.86), respectively.ConclusionItaly experienced a nearly 2.6-fold increase in neuroinvasive TOSV incidence in 2022-23 vs 2016-21. Raising public awareness on risk factors and personal protection measures may enhance prevention efforts.

Toscana virus - an emerging Mediterranean arbovirus transmitted by sand flies

Toscana virus (TOSV) is an emerging arthropod-borne virus (arbovirus) of medical importance that is increasing its range across much of the Mediterranean Basin, Europe and the Middle East. Transmitted by Phlebotomus spp. sand flies, it is the most clinically relevant sand fly-borne phlebovirus. Initially isolated in the Tuscany region of Central Italy, it has now been detected in multiple countries that surround this geographical area. Infection of the vertebrate host can cause fever and neurological disease, following the dissemination of the virus to the brain. The prevalence is high in some regions, with a notable percentage of individuals showing seroconversion. TOSV can be a leading cause of acute meningitis and encephalitis (AME) during the summer months. In this comprehensive review, we will focus on several key topics. We discuss how TOSV has spread to establish outbreaks of infection in both humans and animals around the Mediterranean and the wider region. Clinical aspects of TOSV infection in humans are described, along with the best standards in diagnosis. Finally, we focus our discussion on the role of the sand fly vector, describing their biology, vector competency, implications for putative vertebrate reservoirs, the effect of the climate emergency on sand fly distribution and the putative role that sand fly-derived salivary factors may have on modulating host susceptibility to TOSV infection.

Sand flies and Toscana virus: Intra-vector infection dynamics and impact on Phlebotomus perniciosus life-history traits

Toscana virus (TOSV) is a leading cause of summer viral meningitis in Southern Europe (Central Italy, south of France, Spain and Portugal) and can cause severe neurological cases. Within the Mediterranean basin, it is transmitted by hematophagous sand flies belonging to the Phlebotomus genus. Despite the identification of the primary TOSV vectors, the viral developmental cycle in vector species remains largely unknown. Limited research has been conducted on transmission dynamics and the vector competence and vectorial capacity of the principal TOSV vector, Phlebotomus perniciosus. In this context, we investigated the intra-vector TOSV infection dynamics in Ph. perniciosus, as well as its impact on the vector life history traits. Female sand flies were experimentally infected with TOSV through an artificial blood meal. Systemic dissemination of the virus was observed approximately three days post-infection, potentially resulting in a short extrinsic incubation period. Moreover, the study revealed a longer hatching time for eggs laid by infected females. This research brought additional experimental insights regarding the vector competence of Ph. perniciosus but also provided the first insight into TOSV developmental cycle and its impact on the vector. These findings prompt further exploration of TOSV transmission dynamics, raise new hypotheses on the virus transmission and highlight the importance of follow-up studies.

Phlebotomine sand fly distribution and abundance in France: A systematic review

Global changes in climate are contributing to modified Phlebotomine sand fly presence and activity, and the distribution of the pathogens they transmit (e.g., Leishmania and Phlebovirus), and are leading to their possible extension toward northern France. To predict the evolution of these pathogens and control their spread, it is essential to identify and characterize the presence and abundance of potential vectors. However, there are no recent publications describing sand fly species distribution in France. Consequently, we carried out a systematic review to provide distribution and abundance maps over time, along with a simplified dichotomous key for species in France. The review adhered to PRISMA guidelines, resulting in 172 relevant capture reports from 168 studies out of the 2646 documents retrieved, of which 552 were read and 228 analyzed. Seven species were recorded and categorized into three groups based on their abundance: low abundance species, abundant but little-studied species, and abundant vector species. Sand flies are certainly present throughout France but there is a greater diversity of species in the Mediterranean region. Phlebotomus perniciosus and Ph. ariasi are the most abundant and widely distributed species, playing a role as vectors of Leishmania. Sergentomyia minuta, though very abundant, remains under-studied, highlighting the need for further research. Phlebotomus papatasi, Ph. perfiliewi, Ph. sergenti, and Ph. mascittii are present in low numbers and are less documented, limiting understanding of their potential role as vectors. This work provides the necessary basis for comparison of field data generated in the future.

Seroprevalence of Toscana and sandfly fever Sicilian viruses in humans and livestock animals from western Saudi Arabia

High seroprevalence rates of several phleboviruses have been reported in domestic animals and humans in sandfly-infested regions. Sandfly Fever Sicilian virus (SFSV) and Toscana virus (TOSV) are two of these viruses commonly transmitted by Phlebotomus sandflies. While SFSV can cause rapidly resolving mild febrile illness, TOSV could involve the central nervous system (CNS), causing diseases ranging from aseptic meningitis to meningoencephalitis. Sandfly-associated phleboviruses have not been investigated before in Saudi Arabia and are potential causes of infection given the prevalence of sandflies in the country. Here, we investigated the seroprevalence of SFSV and TOSV in the western region of Saudi Arabia in samples collected from blood donors, livestock animals, and animal handlers. An overall seroprevalence of 9.4% and 0.8% was found in humans for SFSV and TOSV, respectively. Seropositivity was significantly higher in non-Saudis compared to Saudis and increased significantly with age especially for SFSV. The highest seropositivity rate was among samples collected from animal handlers. Specifically, in blood donors, 6.4% and 0.7% tested positive for SFSV and TOSV nAbs, respectively. Animal handlers showed higher seroprevalence rates of 16% and 1% for anti-SFSV and anti-TOSV nAbs, respectively, suggesting that contact with livestock animals could be a risk factor. Indeed, sera from livestock animals showed seropositivity of 53.3% and 4.4% in cows, 27.5% and 7.8% in sheep, 2.2% and 0.0% in goats, and 10.0% and 2.3% in camels for SFSV and TOSV, respectively. Together, these results suggest that both SFSV and TOSV are circulating in the western region of Saudi Arabia in humans and livestock animals, albeit at different rates, and that age and contact with livestock animals could represent risk factors for infection with these viruses.

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.

Melittin-Related Peptides Interfere with Sandfly Fever Naples Virus Infection by Interacting with Heparan Sulphate

Emerging viruses pose an important global public health challenge, and early action is needed to control their spread. The Bunyaviridae family contains a great number of arboviruses which are potentially pathogenic for humans. For example, phleboviruses affect a large range of hosts, including humans and animals. Some infections usually have an asymptomatic course, but others lead to severe complications, such as Toscana virus, which is able to cause meningitis and encephalitis. Unfortunately, to date, no vaccines or antiviral treatments have been found. In the present study, we evaluated the effect of melittin-related peptides, namely the frog-derived RV-23 and AR-23, on sandfly fever Naples virus infection in vitro. Both peptides exhibited a strong antiviral activity by targeting the viral particles and blocking the virus-cell interaction. Their action was directed to an early phase of SFNV infection, in particular at viral adsorption on host cells, by interfering with the binding of common glycosaminoglycan receptors. Given the better antimicrobial behavior of AR-23 and RV-23 compared to melittin in terms of selectivity, our studies expand our understanding of the potential of these peptides as antimicrobials and stimulate further investigations in the direction of novel antiviral strategies against phlebovirus infection.

Epidemiology, Isolation, and Genetic Characterization of Toscana Virus in Algerian Patients Displaying Neurological Infection, 2016-2018

Purpose

The current study reports the results of the diagnosis of neuro-invasive Toscana virus (TOSV) infection in Algeria between 2016 and 2018 and describes the first isolation of TOSV strain from human samples in North Africa.

Materiel and methods

Cerebrospinal fluid (CSF) and sera samples were obtained from 720 hospitalized patients displaying neurological infection symptoms of unknown etiology, of which 604 were screened for TOSV. The diagnosis was performed by serological and/or RT-PCR tests. In addition, TOSV was isolated in vivo and in vitro from CSF and genetically characterized.

Results

23 cases of TOSV neurological infections were detected. Cases were located in 11 Wilayas (administrative provinces), mainly in northern Algeria. In addition, we report the isolation of TOSV strain belonging to lineage A from human samples with its complete coding sequence.

Conclusion

Even though the number of infections is probably underestimated, TOSV is endemic in Algeria, with several cases of neuro-invasive diseases in humans recorded each year. Therefore, the diagnosis of TOSV should be included in the differential diagnosis of neurological diseases, especially aseptic meningitis, during the period of activity of the phlebotomine vector. Further studies are required to measure precisely the nationwide prevalence of TOSV in Algeria.

Persistence of Toscana virus in sugar and blood meals of phlebotomine sand flies: epidemiological and experimental consequences

Many virological studies have tested the persistence of enveloped RNA viruses in various environmental and laboratory conditions and shown their short-term persistence. In this article, we analyzed Toscana virus (TOSV) infectivity, a pathogenic sandfly-borne phlebovirus, in two different conditions: in the sugar meal and blood meal of sand flies. Our results showed that TOSV RNA was detectable up to 15 days in sugar solution at 26 °C and up to 6 h in blood at 37 °C. Moreover, TOSV remains infective for 7 days in sugar solution and for minimum 6 h in rabbit blood. TOSV has shown persistent infectivity/viability under different conditions, which may have important epidemiological consequences. These results strengthen new hypotheses about the TOSV natural cycle, such as the possibility of horizontal transmission between sand flies through infected sugar meal.

Sandfly-Borne Phleboviruses in Portugal: Four and Still Counting

According to ICTV, there are currently 66 known phlebovirus species. More than 40 of these viruses were isolated or detected in phlebotomine sandflies and some of them are known pathogens. In Portugal, information about sandfly-borne phleboviruses is scarce and scattered sandfly-borne diseases are neglected and often not considered in differential diagnoses. The main objective of this work was to gather the existing information and to raise awareness about the circulating phleboviruses in this country. To date, Massilia and Alcube phleboviruses have been isolated from sandflies in southern Portugal. Human infections with Toscana and Sicilian phleboviruses have been reported, as well as seroprevalence in cats and dogs. More studies are needed in order to understand if the viruses isolated during the entomological surveys have an impact on human health and to fully understand the real importance of the already recognized pathogens in our country.