Broader Geographical Distribution of Toscana Virus in the Mediterranean Region Suggests the Existence of Larger Varieties of Sand Fly Vectors

Abstract

Toscana virus (TOSV) is endemic in the Mediterranean basin, where it is transmitted by sand flies. TOSV can infect humans and cause febrile illness as well as neuroinvasive infections affecting the central and peripheral nervous systems. Although TOSV is a significant human pathogen, it remains neglected and there are consequently many gaps of knowledge. Recent seroepidemiology studies and case reports showed that TOSV's geographic distribution is much wider than was assumed a decade ago. The apparent extension of the TOSV circulation area raises the question of the sandfly species that are able to transmit the virus in natural conditions. Phlebotomus (Ph.) perniciosus and Ph. perfiliewi were historically identified as competent species. Recent results suggest that other species of sand flies could be competent for TOSV maintenance and transmission. Here we organize current knowledge in entomology, epidemiology, and virology supporting the possible existence of additional phlebotomine species such as Ph. longicuspis, Ph. sergenti, Ph. tobbi, Ph. neglectus, and Sergentomyia minuta in TOSV maintenance. We also highlight some of the knowledge gaps to be addressed in future studies.

Keywords: Bunyavirales; Mediterranean area; Phenuiviridae; Phlebotomus; Sandfly fever Naples phlebovirus; Sergentomyia; Toscana virus; arbovirus; arthropod-borne; phlebotomine; sand fly; sandfly.

Figure 1

Phylogenetic analysis of Toscana virus (TOSV) based on the nucleocapsid protein gene. Maximum likelihood analysis at nucleotide level was performed using the MEGA 6.06 software program [15]. Bootstrap values are indicated and correspond to 1000 pseudoreplications.

Figure 2

Geographical distribution of Toscana virus (TOSV) and reported distribution of predominant sand fly species in the countries where TOSV is present.