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West Nile virus (WNV) transmission has been confirmed in the last four years in Europe and in the Mediterranean Basin. An increasing concern towards West Nile disease (WND) has been observed due to the high number of human and animal cases reported in these areas confirming the importance of this zoonosis. A new epidemiological scenario is currently emerging: although new introductions of the virus from abroad are always possible, confirming the epidemiological role played by migratory birds, the infection endemisation in some European territories today is a reality supported by the constant reoccurrence of the same strains across years in the same geographical areas. Despite the WND reoccurrence in the Old World, the overwintering mechanisms are not well known, and the role of local resident birds or mosquitoes in this context is poorly understood. A recent new epidemiological scenario is the spread of lineage 2 strain across European and Mediterranean countries in regions where lineage 1 strain is still circulating creating favourable conditions for genetic reassortments and emergence of new strains. This paper summarizes the main epidemiological findings on WNV occurrence in Europe and in the Mediterranean Basin from 2009 to 2013, considering potential future spread patterns.

SummaryThe interaction between living beings, including men, animals and pathogens, sharing the same environment, should be considered as a unique dynamic system, in which the health of each component is inextricably interconnected and dependent with the others. Nowadays, a new integrated One Health approach is reflecting this interdependence with a holistic view to the ecological system. The One Health approach can be defined as a collaborative and a multidisciplinary effort at local, national and global level to guarantee an optimal healthy status for humans, animals and environment. Strictly related to the One Health concept is to be considered the control of infectious diseases, which have influenced the course of human history. Four different components might be identified as key elements within the 'One World -One Health' (OWOH) approach: the geographical component, the ecological one, the human activities and the food-agricultural ones.

West Nile virus (WNV) is a mosquito-transmitted Flavivirus belonging to the Japanese encephalitis antigenic complex of the Flaviviridae family. Its spread in the Mediterranean basin and the Balkans poses a significant risk to human health and forces public health officials to constantly monitor the virus transmission to ensure prompt application of preventive measures. In this context, predictive tools indicating the areas and periods at major risk of WNV transmission are of paramount importance. Spatial analysis approaches, which use environmental and climatic variables to find suitable habitats for WNV spread, can enhance predictive techniques. Using the Mahalanobis Distance statistic, areas ecologically most suitable for sustaining WNV transmission were identified in the Mediterranean basin and Central Europe. About 270 human and equine clinical cases notified in Italy, Greece, Portugal, Morocco, and Tunisia, between 2008 and 2012, have been considered. The environmental variables included in the model were altitude, slope, night time Land Surface Temperature, Normalized Difference Vegetation Index, Enhanced Vegetation Index, and daily temperature range. Seasonality of mosquito population has been modelled and included in the analyses to produce monthly maps of suitable areas for West Nile Disease. Between May and July, the most suitable areas are located in Tunisia, Libya, Egypt, and North Cyprus. Summer/Autumn months, particularly between August and October, characterize the suitability in Italy, France, Spain, the Balkan countries, Morocco, North Tunisia, the Mediterranean coast of Africa, and the Middle East. The persistence of suitable conditions in December is confined to the coastal areas of Morocco, Tunisia, Libya, Egypt, and Israel.

In 2013, the circulation of West Nile virus (WNV) was detected in the Lombardy region and the following year a surveillance programme was activated with the aim of early identification of the viral distribution in mosquitoes and wild birds. A total of 50 959 Culex spp. mosquitoes grouped in six hundred and forty-seven pools as well as 1400 birds were screened by RT-PCR for the presence of West Nile virus leading to the identification of the viral genome in 32 mosquito pools and 13 wild birds. The surveillance was able to detect the WNV circulation on an average of 42 days (CI 95% 29.98-53.86; Student's t-distribution) before the occurrence of human West Nile disease (WND) cases in the same area. These results demonstrate the presence of WNV in the Lombardy region and confirm entomological and wild birds surveillance as an effective measure for the early identification of WNV circulation in infected areas, thus providing a useful and cost-effective tool for the public health authorities in the application of measures to prevent human infection.

Migratory birds are considered one of the main sources for West Nile virus (WNV) introduction into European countries. Following the WNV epidemic in the late summer of 1998 in a marshy area of Tuscany (Padule of Fucecchio), an extensive ornithological surveillance programme was carried out in the infected areas from 2006 to 2008. Several species of migratory and resident birds were trapped, sampled and serologically tested. The results of this surveillance programme gave a useful indication of potential sources of WNV re-introduction and spread into Italy. The area under study was also investigated and classified into ecological areas through satellite image processing. In August 2008, the WNV infection re-emerged in Italy in the area surrounding the Po river delta, involving three regions: Lombardy, Emilia Romagna and Veneto. Several surveillance activities were immediately put in place, including the extensive monitoring of wild birds found dead or trapped in the framework of other surveillance programmes. These activities were also prolonged in the 2009, when the virus circulation re-occurred at the border of the area already infected in 2008. The possible epidemiological role of the different species of migratory and resident birds is discussed, in relation to the different ecological patterns identified in the area and their potential ability to introduce, spread and support the endemization of WNV infection.

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The epidemiology of West Nile disease (WND) is influenced by multiple ecological factors and, therefore, integrated surveillance systems are needed for early detecting the infection and activating consequent control actions. As different animal species have different importance in the maintenance and in the spread of the infection, a multispecies surveillance approach is required. An integrated and comprehensive surveillance system is in place in Italy aiming at early detecting the virus introduction, monitoring the possible infection spread, and implementing preventive measures for human health. This paper describes the integrated surveillance system for WND in Italy, which incorporates data from veterinary and human side in order to evaluate the burden of infection in animals and humans and provide the public health authorities at regional and national levels with the information needed for a fine tune response.