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

Abstract

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.

Sand flies and Toscana virus: intra-vector infection dynamics and impact onPhlebotomus perniciosuslife-history traits

“…perniciosus between three and six dpi although this should be confirmed by fine dissection and testing of only the salivary glands. In addition, the release of TOSV into sugar meal together with recent demonstration of long-term persistence of infectious TOSV in sugar meal (up to 7 days at 26°C) (13) suggest that sand fly to sand fly transmission can occur orally during sap feeding in nature. To better understand the transmission dynamics and be able to predict TOSV emergence it would be crucial to investigate further the possible alternative transmission routes of TOSV between sand flies through their sugar meal.…”

“…Toscana virus transmission dynamics within sand fly vectors and vertebrate hosts, including proven and suspected transmission routes, animals identified positive for TOSV-specific antibodies suspected but not identified as reservoirs, and incubation period estimates within the vector (EIP: Extrinsic Incubation Period) and the human neuroinvasive host (IIP: Intrinsic Incubation Period) (7,8,59–62,10,13,14,54–58). …”

“…Feeding was performed for six hours, with reduced brightness, and regular manual blood mix to avoid clotting. Six hours of blood feeding was chosen as TOSV remains infectious and at the same amount in the blood meal under these conditions as previously described (13). As engorged females are fragile, it is recommended to handle them after the first 24 hours of digestion (63).…”

“…perniciosus (6), their significance in the natural TOSV cycle remains uncertain and warrants further investigation. Recently it was hypothesized that transmission from infected to uninfected sand flies during sugar feeding might play a significant role in the virus natural cycle (13). This mode of transmission has already been shown experimentally with Massilia virus, another phlebovirus genetically related to TOSV (14).…”

“…This mode of transmission has already been shown experimentally with Massilia virus, another phlebovirus genetically related to TOSV (14). Moreover, TOSV persistence and infectivity in sand fly sugar meal has recently been demonstrated in laboratory conditions (13). Nevertheless, the relevance of this alternative transmission route to TOSV cycle in natural ecosystems remains to be confirmed.…”