Identification of Toscana Virus in Natural Population of Sand flies (Diptera: Psychodidae) from Moroccan Leishmaniasis foci

Susceptibility of diverse sand fly species to Toscana virus

Toscana virus (TOSV) is an emerging but neglected human pathogen currently circulating around the Mediterranean basin including North Africa. Human illness ranges from asymptomatic or mild flu-like syndromes to severe neurological diseases such as meningitis or meningoencephalitis. Despite its significant impact, understanding of TOSV transmission and epidemiology remains limited. Sand flies (Diptera: Phlebotominae), specifically Phlebotomus perniciosus and Phlebotomus perfiliewi, are believed to be the primary vectors of TOSV. However, the spread of TOSV to new geographical areas and its detection in other sand fly species suggest that additional species play a role in the circulation and transmission of this virus. This study investigated the vector competence of four sand fly species - P. tobbi, P. sergenti, P. papatasi, and Sergentomyia schwetzi - for two TOSV strains: 1500590 (TOSV A lineage) and MRS20104319501 (TOSV B lineage). Sand flies were orally challenged with TOSV via bloodmeals. None of the tested species showed susceptibility to the TOSV A strain. However, for TOSV B strain, P. tobbi demonstrated a high potential as a new vector, exhibiting high infection and dissemination rates. P. sergenti also showed some susceptibility to TOSV B, with the virus dissemination observed in all infected females. These finding suggests that P. tobbi and P. sergenti are new potential vectors for TOSV B. Given that P. tobbi and P. sergenti are the primary vectors of human leishmaniases in the Balkans, Turkey and Middle East, their susceptibility to TOSV could have significant epidemiological consequences. On the other hand, P. papatasi and S. schwetzi appeared refractory to TOSV B infection. Refractoriness of P. papatasi, a highly anthropophilic species distributed from the Mediterranean to the Middle East and India, suggests that this species does not contribute to TOSV circulation.

Epidemiology of Sandfly-Borne Phleboviruses in North Africa: An Overview

Eight sandfly-borne phleboviruses were found to circulate in North Africa. Phleboviruses detected in sandflies were Toscana (TOSV), Sandfly Fever Sicilian (SFSV), Sandfly Fever Naples (SFNV), Cyprus (CYPV), Punique (PUNV), Utique, Saddaguia, and Medjerda Valley (MVV) viruses, yielding an overall infection rate of 0.02-0.6%. Phlebotomus perniciosus and Phlebotomus longicuspis were the most common vector species in the region. TOSV seroprevalence in dogs from Algeria (4.56%) and Tunisia (7.5%) was low and close, unlike SFSV (38.1%) and PUNV (43.5%), which were restricted to Tunisia. SFSV (1.3-21%) and TOSV (3.8-50%) were the most prevalent among humans. TOSV was frequently detected and symptomatically confirmed in both Algeria (3.8%) and Tunisia (12.86%). Other sandfly-borne phleboviruses have also been detected but less importantly, such as SFNV in Morocco (2.9%) and Tunisia (1.1%) and PUNV (8.72%), CYPV (2.9%), and MVV (1.35%) in Tunisia. Their distribution was mainly northern. Overall, 15.9% of the healthy population were seropositive for sandfly-borne phleboviruses, with evidenced cocirculation. Noticeably, studies conducted in Morocco were mostly interested in TOSV in sandflies. Available data from Libya and Egypt were scant or historical. Further elaboration is required to check the sporadic detection of less-prevalent phleboviruses and fully elucidate the epidemiological situation.

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.

New Isolation of Ponticelli III Virus (Bunyavirales: Phenuiviridae) in Emilia-Romagna Region, Italy

The number of newly described sandfly-borne phleboviruses has been steadily growing in recent years. Some phleboviruses are human pathogens, but their health relevance is largely uncharacterized. We aimed to investigate the circulation of these viruses in the Emilia-Romagna region where several have already been described. A total of 482 sandflies were collected in a site in Reggio Emilia in 2019 and 2020. Sandflies collected in 2020 were grouped in 21 pools with a maximum of 25 sandflies per pool, submitted to real time PCR, and isolated in Vero cell culture. Complete genome sequencing showed the isolation of a strain of a Ponticelli III virus. This virus, which belongs to the species Adana phlebovirus, differed in the M segment from the Ponticelli I and Ponticelli II viruses. Analysis performed on the genomic segments of the newly isolated virus compared with other phleboviruses highlighted a strong purifying selection in the L segments, and different substitution saturation, highest in the M segments. Future research should address the ecological processes driving the occurrence of these novel phleboviruses and their possible impact on public health.