Seroprevalence of Antibodies to Sandfly Fever Sicilian Virus in a Sample Population in Tuscany,Italy

Introduction

S andfly fever viruses cause human illness and are transmitted by sandfly vectors (Phlebotomus spp.). Phleboviruses, in particular, the Sandfly Naples (SFNV), Sandfly Sicilian (SFSV), and Toscana (TOSV) viruses circulate in the Mediterranean basin (Izri et al. 2008, Calamusa et al. 2012, Ergünay et al. 2011, Guler et al. 2012). In endemic areas, these infections occur during the warm season, in parallel with the highest activity of sandfly vectors. TOSV has been considered the etiologic agent of acute meningitis, meningoencephalitis, or encephalitis. Naples and Sicilian serotype viruses are the etiologic agents of a usually mild, self-limited disease characterized by fever, myalgia, headache, and muscle and joint pain, and patients generally recover within a week. SFSV, which is specially transmitted by Phlebotomus papatasi (Karabatos 1985) was discovered in Italy (Palermo, Sicily) where it affected Allied Army troops in World War II after landings in Sicily in 1943. In Italy, P. papatasi is scarce, but it was abundant before dichlorodiphenyltrichloroethane (DDT) was used in the 1940s, and it may have been substituted by other vectors belonging to the subgenus Larroussius for SFSV transmission.

More recently, 37 cases of SFSV infection were recorded in Swedish tourists returning from Cyprus between 1986 and 1989 (Eitrem et al. 1990), and an outbreak affecting 286 Greek soldiers stationed in Cyprus occurred in 2002 (Konstantinou et al. 2007). This virus and SFSV-like viruses are now circulating in Italy, Egypt, Cyprus, Iran, Israel, Algeria, Tunisia, and Pakistan (Depaquit et al. 2012). A recent seroepidemiological study conducted on a population sample in Sicily showed that 9.2% of the subjects were positive for SFSV immunoglobulin G (IgG), and this percentage was about 2-fold higher in subjects over the age of 64 (15.9%) compared to the youngest (7%) (Calamusa et al. 2012). It seems likely that the oldest subjects were heavily exposed to P. papatasi, the main SFSV vector, when they were young, after which the sandfly was markedly suppressed by the extensive use of DDT (Calamusa et al. 2012).

Data for SFSV seroprevalence in northern and central Italy are lacking, thus our aim was to investigate the seroepidemiology of SFSV in Tuscany, where TOSV is widely diffused. All consecutive serum samples (n=365) submitted to the laboratory of “S. Maria delle Scotte” Hospital in Siena during the winter season 2011, collected from people of different ages for pathologies not related to neurological forms, were included in the study. They were divided into 3 groups of subjects by age: (1) Aged 0–20 years (n=104, median age, 12 years); (2) aged 21–60 years (n=120, median age, 41 years); and (3) aged >60 years (n=141, median age, 74 years). The tested population was composed of 195 males and 170 females. All patients in the study lived in Siena or its suburbs. Sera were analyzed for the presence of specific anti-SFSV IgM and IgG antibodies by indirect immunofluorescence assay (EuroImmun, Germany). None of the serum was positive for IgM, but 4 samples (1.09 %) were IgG positive to SFSV (Table 1).

A comparison of these data with that observed in Sicily showed that the virus is not circulating in Tuscany, whereas it is still present in Sicily, where seropositivity to SFSV has been recorded in the analyzed population (Calamusa et al. 2012). We could hypothesize that the virus is not present in central Italy or that its vector is not circulating in the area considered in this study. Currently, phlebotomine sandflies are the main vector of Toscana virus, which is widely diffuse in central Italy, and it is possible that P. papatasi, the vector of SFSV, is less diffuse among the species of the Phlebotomidae family, due to the past use of insecticides; however, this feature does not justify the low seroprevalence rate, because other sandflies have been recognized as vectors for the SFSV (Cusi et al. 2010, Moureau et al. 2010). The 4 patients that resulted positive for SFSV IgG were over 70 years old; thus, we do not know whether they acquired the infection outside Tuscany or if their seropositivity dates back to their youth when the virus might have been circulating in central Italy.

SFSV-like viruses are diffuse in the Mediterranean basin and some recent reports have described the presence of these new viruses by serological analyses on the human population (Izri et al. 2008, Ergünay et al. 2011, Calamusa et al. 2012, Guler et al. 2012). The results obtained in Tuscany are in line with those observed in the south of France, where SFSV does not appear to be circulating (Bichaud et al. 2011). The seroprevalence to TOSV in central Italy and Tuscany is quite high (20–21%) (Terrosi et al. 2009); thus, it was interesting to analyze the seroprevalence of another sandfly virus transmitted by the same vectors in the same area. This study shows that SFSV is not endemic in Tuscany and, unlike Sicily, seroprevalence is rather low, confirming that this virus does not play an important role in the etiology of febrile illness in central Italy during the warmest months of the year.