Dogs as sentinel hosts for sand-fly-borne infections in the Mediterranean Basin: a multinational serological survey

Phlebotomine sand-fly-borne infections are an emerging threat to human and animal health in Mediterranean countries, highlighting the need for improved surveillance and control strategies. Dogs are ideal sentinel hosts owing to their central role in the transmission of zoonotic Leishmania infantum, frequent exposure to sand fly bites, capacity to develop antibodies to phleboviruses, and close contact with humans. This study reports cross-sectional surveys of antibodies to Leishmania, Toscana virus (TOSV), and Sicilian sand fly virus (SFSV) in dogs from Portugal, Spain, Italy, Croatian Istria, Turkey, and Israel, as well as antibodies to salivary proteins of Phlebotomus perniciosus (Portugal, Spain, and Italy) and Phlebotomus papatasi (Spain and Italy), conducted within the Climate Monitoring and Decision Support Framework for the Detection and Mitigation of Sand fly Diseases with Cost-Benefit and Climate Policy Measures (CLIMOS) project.

Blood samples and epidemiological data were collected from 2500 dogs. Antibodies to Leishmania were detected by indirect immunofluorescence, phlebovirus antibodies by seroneutralization assays, and antibodies to P. perniciosus and P. papatasi salivary antigens by enzyme-linked immunosorbent assay (ELISA) using recombinant proteins rSP03B and rSP36, respectively. Sources of antibody variability were evaluated using mixed-effects logistic regression models.

Antibodies to L. infantum, phleboviruses, and sand fly saliva were widely detected, although seroprevalence varied markedly by region. No Leishmania-seropositive dogs were found in Istria, parts of northern Spain, or several districts in Israel, whereas seroprevalence exceeded 30% in Sicily and in several Turkish and Spanish provinces. TOSV seropositivity was generally absent or below 5%, except in southern Spain (8-24%) and Muğla, Turkey (10%). SFSV exposure was highly focal, occurring mainly in Turkey (12%), Israel (12%), and Lisbon (7%). Exposure to P. perniciosus was very high in Portugal, Sicily, and most of Spain, while P. papatasi exposure was highest in Sicily and selected Spanish regions. Antibody variability was driven primarily by geographical location.

The marked geographical heterogeneity observed confirms dogs as valuable sentinels for sand-fly-borne infections. These infections are highly clustered across Mediterranean regions, likely reflecting differences in sand fly density and infection rates. Understanding the drivers of this heterogeneity is essential for accurate risk mapping and effective control strategies.