Spatio-temporal pattern and climatic determinants of Visceral Leishmaniasis in Italy

Abstract

BACKGROUND AND AIM: Historically, leishmaniasis in Italy was constrained to areas with Mediterranean climate. In the last 20 years, sand fly vectors and cases of human Visceral Leishmaniasis (VL) have been detected in Northern Italian regions, traditionally classified as cold areas unsuitable for sand fly survival. We aimed to study the spatio-temporal pattern and climatic determinants of VL incidence in Italy. METHODS: National Hospital Discharge Register (HDR) records were used to identify incident VL cases between 2010 and 2017 (ICD-9-CM code: 085.0). Incident rates were computed for each year of study (N=8) and for each Italian province (N= 110). Temperature and precipitation data were obtained from the latest ERA5-Land database climate re-analysis (9 km of spatial resolution) and expressed as year and province-specific seasonal average temperature and cumulative precipitation. Incident cases were modelled with a Bayesian spatio-temporal conditional autoregressive Poisson models to quantify how disease risk was influenced by the climatic parameters. RESULTS:We identified 1123 VL cases (Crude Incidence Rate: 2.4 cases /1,000,000 person-years). The highest incidence rates were observed in Southern Italy, although high incidence rates were observed also in some areas of Northern Italy. VL incidence resulted positively associated with air temperatures (Incidence Rate Ratios (IRR) for 1°C increase in winter average temperature: 1.17, 95% Credible Interval (CI): 1.13-1.19, IRR for 1°C increase in summer average temperature: 1.06, 95% CI: 1.00-1.13) and inversely associated with cumulative precipitation (IRR for 10 mm increase in summer cumulative precipitation: 0.99, 95% CI: 0.98-1.00). CONCLUSIONS:The current findings indicate that VL is endemic in the whole Italian peninsula and that climatic factors, as air temperature and precipitation, might play a relevant role in shaping VL incidence. These results suggest also that climate change might affect the future spread of leishmaniasis. KEYWORDS: One-Health, Spatial Epidemiology, Climate-change, Vector-borne diseases, Environmental Epidemiology