Spatio-Temporal Pattern and Meteo-Climatic Determinants of Visceral Leishmaniasis in Italy

Abstract

Historically, visceral leishmaniasis (VL) in Italy was constrained to Mediterranean areas. However, in the last 20 years, sand fly vectors and human cases of VL have been detected in northern Italy, traditionally classified as a cold area unsuitable for sand fly survival. We aim to study the spatio-temporal pattern and climatic determinants of VL incidence in Italy. National Hospital Discharge Register records were used to identify incident cases of VL between 2009 and 2016. Incident rates were computed for each year (N = 8) and for each province (N = 110). Data on mean temperature and cumulative precipitation were obtained from the ERA5-Land re-analysis. Age- and sex-standardized incidence rates were modeled with Bayesian spatial and spatio-temporal conditional autoregressive Poisson models in relation to the meteo-climatic parameters. Statistical inference was based on Monte Carlo−Markov chains. We identified 1123 VL cases (incidence rate: 2.4 cases/1,000,000 person-years). The highest incidence rates were observed in southern Italy, even though some areas of northern Italy experienced high incidence rates. Overall, in the spatial analysis, VL incidence rates were positively associated with average air temperatures (β for 1 °C increase in average mean average temperature: 0.14; 95% credible intervals (CrI): 0.01, 0.27) and inversely associated with average precipitation (β for 20 mm increase in average summer cumulative precipitation: −0.28, 95% CrI: −0.42, −0.13). In the spatio-temporal analysis, no association between VL cases and season-year specific temperature and precipitation anomalies was detected. Our findings indicate that VL is endemic in the whole Italian peninsula and that climatic factors, such as air temperature and precipitation, might play a relevant role in shaping the geographical distribution of VL cases. These results support that climate change might affect leishmaniasis distribution in the future.

Keywords: environmental epidemiology; meteo-climatic impacts; spatio-temporal epidemiology; visceral Leishmaniasis.

Figure 1

Year-specific VL standardized incidence rates between 2009 and 2016. Age and sex standardized IR are expressed per 10⁶ person-years and were computed with direct standardization using the Italian census data of 2011 as reference population. Estimates are represented as dashed lines, while the 95% CI bands are represented as shaded areas.

Figure 2

Average age- and sex-specific VL incidence rates over the 2009–2016 period. Incidence rates are expressed per 10⁶ person-years and were computed using the Italian census data of 2011. Estimates are represented as dashed lines, while the 95% CI bands are represented as shaded areas.

Figure 3

VL standardized incidence rates by Italian provinces (2009–2016). Choropleth map representing VL standardized incidence ratio (SIR) at province level for the 2009–2016 period. Provinces with higher risk than the Italian average (SIR > 1.10) are represented in shades of red, while provinces with lower risk (SIR < 0.90) are represented in shades of blue.