The Entomological Surveillance As a Tool for the Early Detection of Mosquito-Borne Diseases: the Experience of Piemonte, Liguria and Valle D’aosta (northwestern Italy)

Purpose: This work describes the entomological surveillance carried out in Piedmont, Liguria and Valle d’Aosta (Northwestern Italy) that allowed the detection of West Nile Virus (WNV) before the occurrence of human cases. This diagnostic approach is focused to all major mosquito-borne flaviviruses of medical interest. Methods & Materials: During the vector season, mosquito traps were located fortnightly in selected sites according to risk factors. Adult females were counted, identified to the species level and pooled by collection site, date and species with a maximum of 100 specimens. After RNA extraction, pools were analysed by Real Time RT-PCR distinctive for WNV Lineage 1 and Lineage 2 and USUTU virus (USUV). Furthermore, a Flavivirus End-point RT-PCR was performed on pools collected in higher risk sites for the introduction of exotic invasive species and pathogens (international airports, ports and connection points, infectious diseases hospitals). Positive pools were sequenced to confirm the specificity of reaction and sent to the National Reference Centre for Animal Exotic Diseases (CESME, IZSAM) for confirmation. Results: Since 2011, about 2,700 pools were analysed. The analysis revealed USUV circulation in Piedmont since 2011 and in Liguria since 2014. In 2014, WNV Lineage 2 was detected in Piedmont (Alessandria province) and Liguria (Genoa province). In 2015, the same virus was found in four different Provinces of Piedmont, showing an expansion of its activity and, at the end of the vector season, the first human case was confirmed. Following WNV detection in mosquitoes, as provided by national legislation, veterinary and human health control measures were activated (screening of equine sera and blood transfusion). Conclusion: The surveillance network allowed to early detect the presence of mosquito-borne flaviviruses potentially pathogenic for humans and animals and provided useful information to public authorities, in order to apply control measures. With particular reference to WNV, our results showed that entomological surveillance can detect the virus in mosquitoes much earlier than in humans, as reported in other Italian regions. Moreover, considering the emergence caused by other flaviviruses of medical interest like Zika or Dengue, the ability of this surveillance protocol to detect Flavivirus spp. could represent an important tool for Public health authorities.