Epidemiologic Relationship between Toscana Virus Infection and Leishmania infantum Due to Common Exposure to Phlebotomus perniciosus Sandfly Vector

Sand flies are recognised vectors of parasites in the genus Leishmania and a number of arthropod-borne viruses, in particular viruses within the genus Phlebovirus, family Bunyaviridae. In southern France, Toscana phlebovirus (TOSV) is recognized as a prominent cause of summer meningitis. Since Leishmania and TOSV have a common vector (Phlebotomus perniciosus), an epidemiologic link has been assumed for a long time. However, there is no scientific evidence of such a link between human leishmaniosis and phleboviral infections. To identify a possible link, we investigated the presence and distribution of antibodies against these two microorganisms (i) in individuals and (ii) at a spatial level in the city of Marseille (south-eastern France). Five hundred sera were selected randomly in the biobank of the Department of Parasitology of the Public Hospitals of Marseille. All sera were previously tested for IgG against Leishmania by Western Blotting, and TOSV IgG were detected by indirect immunofluorescence. The seropositivity rates were 21.4% for TOSV and 28% for Leishmania. Statistical analysis demonstrated that seropositivity for one pathogen was significantly associated with seropositivity to the other pathogen. This result provided the first robust evidence for the existence of an epidemiological relationship between Leishmania infantum and TOSV. Addresses of tested patients were geolocalized and integrated into Geographical Information System software, in order to test spatial relationship between the two pathogens. Spatial analysis did not allow to identify (i) specific patterns for the spatial distribution of positive serological results for TOSV or Leishmania, and (ii) a spatial relationship between Leishmania and TOSV positive serological results. This may reflect the fact that the sample studied was not powerful enough to demonstrate either a spatial clustering or co-location, i.e. that the actual risk exposure area is smaller than the mean of distance between patients in our study (245 m)

Evolution of Leishmania and TOSV seroprevalence in tested population according to age groups.

<p>Evolution of Leishmania and TOSV seroprevalence in tested population according to age groups.</p

Results of analysis of the spatial clustering of positive points.

<p>Positive points for Leishmania, for TOSV and for both pathogens were studied separately. No clustering could be detected: tests showed no difference between observed situations and simulated situations.</p

Analysis of spatial distribution of positive points.

<p>The maps represent the distribution of tested patients for Leishmania parasite (A), Toscana virus (B) and for patients positive for both pathogens (C). The orange dots represent positive sera. The ellipses represent the Standard Deviational Ellipses. The distribution of L-IgG-POS points, TOSV-IgG-POS points and points positive for both L-IgG and TOSV-IgG could not be distinguished from a random distribution amongst the sample tested.</p

Results of the spatial co-location test including the intrinsic correlation.

<p>It was performed in order to test the global relationship between L-IgG-POS and TOSV-IgG-POS individuals. The test showed a significant spatial co-location between the two spatial patterns of positive sera.</p

Results of the spatial co-location test excluding the intrinsic correlation.

<p>It was performed in order to test the global relationship between L-IgG-POS and TOSV-IgG-POS individuals. When the intrinsic correlation was excluded from spatial correlation (<i>i.e.</i> the nearest positive neighbour of a positive point needed to be another object), the tests used showed no significant spatial co-location.</p

Spatial distribution of individuals tested in this study.

<p>Each point corresponds to a postal address. The distribution of the selected sample was found to follow the population density.</p