Circulation of Toscana Virus in a Sample Population of Corsica, France

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.

Prevalence of Toscana Virus Antibodies in Residents of Bulgaria: A Nationwide Study Following the Pandemic of COVID-19

Introduction: Toscana virus (TOSV) is an arthropod-borne virus transmitted by sandflies and is mainly found in countries around the Mediterranean basin. In this article, we present the findings of a seroprevalence study on TOSV in Bulgaria. We aim to assess the current epidemiological situation regarding TOSV in the country and raise clinical awareness. Methods: Serum samples (n = 1892) were collected in December 2023. Serological tests were performed using a commercial anti-TOSV ELISA kit. Results: Specific immunoglobulin G (IgG) antibodies were detected in 6.4% (121/1892) of the participants. A significantly higher seropositivity rate was found in the age group over 65 years compared with the age groups 18-29 and 40-64 (11.8% vs. 3.9% vs. 3.4%), as well as in males compared with females (8.0% vs. 5.3%). The seroprevalence rates in districts ranged from 0% to 18.5%. Higher seropositivity was found in the southern and northern regions. Conclusions: The seroprevalence rate of TOSV in Bulgaria, found in this study, is a significant decrease compared with the seropositivity rate of 24.5% reported in the country in 2018. The reasons for this are unknown and could possibly be related to the COVID-19 pandemic and the constantly changing environmental conditions. There is also a possibility that the higher seropositivity detected in 2018 together with the rise in clinical cases reported from endemic countries around that time might have been due to an unrecognized TOSV outbreak taking place in this period. Continued clinical awareness and surveillance are necessary for recognition and management of potential cases of TOSV neuroinfection, especially during summer.

Sand fly-borne diseases in Europe: epidemiological overview and potential triggers for their emergence and re-emergence

Phlebotomine sand flies (Diptera: Phlebotominae) are vectors of human and animal pathogens, including Leishmania species protozoan parasites and viruses of the genus Phlebovirus. In Europe, visceral zoonotic leishmaniasis caused by Leishmania infantum, a deadly disease when left untreated, is endemic in southern countries, and dogs are the main reservoir hosts for human infection. Most phleboviruses cause asymptomatic infections or flu-like syndromes in humans, but Toscana phlebovirus can cause meningitis and encephalitis. These diseases are likely to re-emerge, posing a growing threat to public and animal health. Potential triggers include the movement of humans and dogs, increasing numbers of immunosuppressive conditions, climate change and other human-mediated environmental changes. An overview of the main epidemiological characteristics of the pathogens transmitted by sand flies in Europe and the potential triggers involved in their emergence and re-emergence are reviewed here. There is a need to implement mandatory notification of human and canine leishmaniases and human phleboviruses and coordinated epidemiological surveillance programmes at a European level, and to raise awareness among healthcare professionals and citizens about sand fly-borne diseases, following a One Health approach.

Exposure to Phlebotomus perniciosus sandfly vectors is positively associated with Toscana virus and Leishmania infantum infection in human blood donors in Murcia Region, southeast Spain

Antibodies against Phlebotomus perniciosus sandfly salivary gland homogenate (SGH) and recombinant protein rSP03B, sandfly-borne Toscana virus (TOSV), Sandfly Fever Sicilian virus (SFSV) and Leishmania, as well as DNA of the latter parasite, were investigated in 670 blood samples from 575 human donors in Murcia Region, southeast Spain, in 2017 and 2018. The estimated SGH and rSP03B seroprevalences were 69% and 88%, respectively, although correlation between test results was relatively low (ρ = 0.39). Similarly, TOSV, SFSV and Leishmania seroprevalences were 26%, 0% and 1%, respectively, and Leishmania PCR prevalence was 2%. Prevalences were significantly greater in 2017, overdispersed and not spatially related to each other although both were positively associated with SGH but not to rSP03B antibody optical densities, questioning the value of the latter as a diagnostic marker for these infections in humans.

Human seroprevalence of Toscana virus and Sicilian phlebovirus in the southwest of Portugal

Toscana virus (TOSV) is emergent in the Mediterranean region and responsible for outbreaks of encephalitis or meningoencephalitis. Sicilian phlebovirus (SFSV) cause epidemics of febrile illness during the summer. The aim of this study was to evaluate the presence of antibodies against TOSV and SFSV in humans in the southwest of Portugal. Neutralizing antibodies to TOSV and SFSV were respectively detected in 5.3% and 4.3% out of 400 human sera tested highlighting the need to increase public health awareness regarding phleboviruses and to include them in the differential diagnosis in patients presenting with fever of short duration and neurological manifestations.

Special Issue "Transmission Dynamics of Insect Viruses"

At the close of this Special Issue of Viruses on the Transmission Dynamics of Insect Viruses, we would like to thank all of the authors for their submissions and the great work expanding our knowledge of insect virus biology and transmission [...].

Development of a Reverse Genetics System for Toscana Virus (Lineage A)

Toscana virus (TOSV) is a Phlebovirus in the Phenuiviridae family, order Bunyavirales, found in the countries surrounding the Mediterranean. TOSV is an important cause of seasonal acute meningitis and encephalitis within its range. Here, we determined the full sequence of the TOSV strain 1500590, a lineage A virus obtained from an infected patient (Marseille, 2007) and used this in combination with other sequence information to construct functional cDNA plasmids encoding the viral L, M, and S antigenomic sequences under the control of the T7 RNA promoter to recover recombinant viruses. Importantly, resequencing identified two single nucleotide changes to a TOSV reference genome, which, when corrected, restored functionality to the polymerase L and made it possible to recover infectious recombinant TOSV (rTOSV) from cDNA, as well as establish a minigenome system. Using reverse genetics, we produced an NSs-deletant rTOSV and also obtained viruses expressing reporter genes instead of NSs. The availability of such a system assists investigating questions that require genetic manipulation of the viral genome, such as investigations into replication and tropism, and beyond these fundamental aspects, also the development of novel vaccine design strategies.

An update on Toscana virus distribution, genetics, medical and diagnostic aspects

BACKGROUND

Toscana virus is an arbovirus transmitted by sand flies within the Mediterranean area where it can cause febrile illness and neuroinvasive infections during the seasonal circulation period of the vector. Although it is an important cause of meningitis and encephalitis, it remains a neglected virus with limited published data, as demonstrated by <250 peer-reviewed articles since the 1970s.

OBJECTIVE

The last review article on Toscana virus was published in 2012. The aim was to compile peer-reviewed articles to provide an updated review highlighting recent findings to complement previous review articles.

SOURCES

PubMed database was searched using the 'Toscana virus' keyword from 2010 to present. A total of 152 articles were retrieved and identified studies were assessed for novel information on virus genetics, and geographic and medical aspects compared with existing knowledge reported in previous review articles.

CONTENT

Studies addressing medical, veterinary and entomological aspects have provided evidence that Toscana virus is present in North Africa, in the Balkan Peninsula, and in most of the Mediterranean islands. Besides the two previously recognized genetic lineages, a novel evolutionary lineage has been identified in the Balkan Peninsula. Co-circulation of two genetic lineages has been demonstrated in France, in Turkey and in Croatia. In addition to meningitis and meningo-encephalitis, which have been reported for 40 years, various neuroinvasive forms have been recently reported such as Guillain-Barré syndrome, hydrocephalus, myositis, fasciitis, polymyeloradiculopathy, deafness and facial paralysis.

IMPLICATION

Because it is endemic in countries bordering the Mediterranean, physicians should include Toscana virus in the differential diagnosis of patients presenting with febrile illness and/or neurological manifestations.