High rates of antibodies against Toscana and Sicilian phleboviruses in common quail Coturnix coturnix birds

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.

Toscana Virus in Wild-Caught Sand Flies in Portugal, Findings from the National Vector Surveillance Network, 2023

Phlebotomine sand flies play a crucial role in both human and veterinary medicine, acting as vectors for Leishmania parasites and most known phleboviruses. In Portugal, the REVIVE program, a comprehensive national surveillance network under the Ministry of Health, has included sand fly surveys since 2016. REVIVE aims to identify existing sand fly species in the country, determine which pathogens are circulating among them, and provide actionable insights for prevention and control measures when necessary. In this way, annually, from May to October, health technicians collect sand flies across mainland Portugal with CDC light traps. The collected sand flies are sent to the Centre for Vectors and Infectious Diseases Research for species identification and molecular screening of pathogens. On 21 September 2023, Toscana virus (TOSV), a well-known phlebovirus in the Mediterranean region due to its capacity to cause neurological disease, was detected in a pool of 30 sand flies collected in Algarve, the southernmost region of Portugal. A 668 bp partial sequence of the nucleoprotein gene shows similarity with TOSV strains from Spain. To our knowledge, this is the first detection of TOSV in its vector in this country, having previously only been reported in vertebrate hosts. These findings highlight the important role of ongoing surveillance efforts in monitoring and understanding the dynamics of sand fly-borne diseases in Portugal.

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.

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.