Quantitative analyses of human West Nile Virus outbreaks in Greece, Hungary, Italy and Romania, 2010-2015.

Spanou, Aphrodite and Mateus, Ceu (2022) Quantitative analyses of human West Nile Virus outbreaks in Greece, Hungary, Italy and Romania, 2010-2015. PhD thesis, Lancaster University.

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Abstract

West Nile Virus (WNV) is a non-communicable, geographically sparce, mosquito borne disease with considerable consequences for human health both at individual and collective level. Since its first isolation in 1937, several geographically spread sporadic, endemic and epidemic outbreaks of WNV disease have been recorded in every continent, except Antarctica. WNV is now the third most prevalent zoonotic febrile infectious disease in the EU. There is a gap in the literature that of synthesising multifactorial data relevant to successive human outbreaks in Europe. To address this gap, this study explored epidemiological, hydro-climatological and environmental data to make meaningful inferences about the composition of human epidemic outbreaks in Europe between 2010-2015. The analysis was based on secondary data collected from the ECDC (European Centre for Disease Prevention and Control), EUROSTAT and ECMWF (European Centre for Medium-Range Weather Forecasts). ECDC and EUROSTAT data were employed to generate the epidemiological profiles of human WNV outbreaks in Hungary, Italy, Greece and Romania which experienced consecutive outbreaks during the studied period. It showed that the ratio of men contracting WNV infections compared to women was higher across all years and countries (Hungary 1.7 (95% CI:1.1 to 2.5), Greece 4 (95% CI:3.4 to 4.8), Italy 4.7 (95% CI: 3.7 to 5.9) and Romania 1.7 (95% CI:1.29 to 2.4)). WNV occurred mostly in those over 65 years of age apart from Hungary (0.3 CI: 0.2 to 0.5) which reported most of its cases in those between 45-64 years of age. It also explored environmental and landscape factors influencing WNV’s distribution across the four south eastern and southern European countries experiencing recurring epidemics. The results suggest that human West Nile disease transmission between 2010 and 2015 occurred in both coastal and non-coastal areas but 63.7% of cases, across the four countries, were detected in non-coastal areas. This result may have been skewed as Hungary’s geography is land locked and Greece did not report any cases in 2015. The study also explored urban, intermediate and rural areas in relation to human WNV outbreaks and the analysis showed a mixed picture. The rise of infections in intermediate and urban areas may indicate that residential infrastructure or population concentration may generate more larval growth which may have led to the outbreaks, but this assertion requires further investigation. Hydroclimatic data on air temperature, dewpoint temperature, soil temperature, total precipitation, relative humidity, surface pressure, volumetric soil water, wind components U (east facing wind velocity) and V (north facing wind velocity) were extracted from the ECMWF’s Re-Analysis (ERA-Interim) system. A zero inflated mixture framework was employed as a means of assessing the relationship between these hydroclimatic parameters and human WNV incidence for the same countries and years. Three nested models were tested: lag0 (same month as the outbreak), lag1 (a month before the outbreak) and lag2 (2 months before a human WNV outbreak occurred). lag2 was the best fitting model. Apart from soil temperature and the V wind component, all other parameters were significant and highly associated with human WNV disease outbreaks in the best fitting model. Further research is needed on subsequent years to confirm the robustness of these findings.