Emerging Trends in the Epidemiology of West Nile and Usutu Virus Infections in Southern Europe

Abstract

The epidemiology of West Nile (WNV) and Usutu virus (USUV) has changed dramatically over the past two decades. Since 1999, there have been regular reports of WNV outbreaks and the virus has expanded its area of circulation in many Southern European countries. After emerging in Italy in 1996, USUV has spread to other countries causing mortality in several bird species. In 2009, USUV seroconversion in horses was reported in Italy. Co-circulation of both viruses was detected in humans, horses and birds. The main vector of WNV and USUV in Europe is Culex pipiens, however, both viruses were found in native Culex mosquito species (Cx. modestus, Cx. perexiguus). Experimental competence to transmit the WNV was also proven for native and invasive mosquitoes of Aedes and Culex genera (Ae. albopictus, Ae. detritus, Cx. torrentium). Recently, Ae. albopictus and Ae. japonicus naturally-infected with USUV were reported. While neuroinvasive human WNV infections are well-documented, USUV infections are sporadically detected. However, there is increasing evidence of a role of USUV in human disease. Seroepidemiological studies showed that USUV circulation is more common than WNV in some endemic regions. Recent data showed that WNV strains detected in humans, horses, birds, and mosquitoes mainly belong to lineage 2. In addition to European USUV lineages, some reports indicate the presence of African USUV lineages as well. The trends in WNV/USUV range and vector expansion are likely to continue in future years. This mini-review provides an update on the epidemiology of WNV and USUV infections in Southern Europe within a multidisciplinary “One Health” context.

West Nile virus in Europe: after action reviews of preparedness and response to the 2018 transmission season in Italy, Slovenia, Serbia and Greece

“…West Nile virus (WNV), a mosquito-borne zoonotic flavivirus, has been emerging in Europe with regular reports of human outbreaks since 1996, mainly in South and South-East European countries, and with a progressive geographic expansion of documented viral circulation [9,10]. The disease has been under European Union/European Economic Area (EU/EEA) surveillance since 2008, showing a seasonal trend with human cases reported typically from early summer to early autumn with a peak in the warmer summer months.…”

“…Genetic lineages 1 and 2 of WNV are associated with human disease with a median estimated incubation period of 2.6 days [12]. WNV lineage 1 was the main lineage circulating in Europe that was associated with human outbreaks until 2004, when WNV lineage 2 was progressively introduced, becoming the main circulating lineage in the region [9].…”

Seasonal and residential clustering at disease onset of anti-MDA5-associated interstitial lung disease

“…Of the many potential environmental factors that may be associated with the onset of PM/DM, infection could be a plausible explanation for this time-space clustering at disease onset. 4 5 In this regard, it has been recognised that some infectious agents can be transmitted by vectors inhabiting near freshwater, whose activity depends on the season, such as mosquitos and migratory birds, 15 16 although it is just a hypothesis of potential environmental factors related to anti-MDA5-associated ILD. On the other hand, recognition of viral RNA by MDA5 initiates activation of NF-κβ and production of type I interferon (IFN) and other proinflammatory cytokines.…”

Comparative Pathology of West Nile Virus in Humans and Non-Human Animals

“…Lineage 2 viruses have been isolated in Africa, Madagascar, the Middle East and Europe [23][24][25][26]. Initially, lineage 1 viruses were considered to be more virulent than lineage 2 viruses; however, it has been shown that both lineages can cause neuroinvasive disease in humans and animals and lineage 2 has now displaced lineage 1 as the primary cause of WNV disease in Europe [23,[27][28][29][30][31].…”