Abstract
BackgroundIn recent years human diseases due to mosquito-borne viruses were increasingly reported in Emilia-Romagna region (Italy), from the chikungunya virus in 2007 to the West Nile virus (WNV) in 2008. An extensive entomological survey was performed in 2009 to establish the presence and distribution of mosquito arboviruses in this region, with particular reference to flaviviruses.Methodology/Principal FindingsFrom May 6 to October 31, a total of 190,516 mosquitoes were sampled in georeferenced stations, grouped in 1,789 pools according date of collection, location, and species, and analyzed by reverse transcription polymerase chain reaction (RT-PCR) to detect the presence of RNA belong to Flavivirus genus. WNV was detected in 27 mosquito pools, producing sequences similar to those of birds and human strains obtained in 2008 outbreak, pointed out the probable virus overwintering. Isolation of WNV was achieved from one of these pools. Moreover 56 pools of mosquitoes tested positive for Usutu virus (USUV). Most PCR positive pools consisted of Culex pipiens, which also was the most analyzed mosquito species (81.4% of specimens); interestingly, USUV RNA was also found in two Aedes albopictus mosquito pools. Simultaneous circulation of WNV and USUV in the survey area was highlighted by occurrence of 8 mosquito WNV- and USUV-positive pools and by the overlaying of the viruses “hot spots”, obtained by kernel density estimation (KDE) analysis. Land use of sampled stations pointed out a higher proportion of WNV-positive Cx. pipiens pool in rural environments respect the provenience of total sampled pool, while the USUV-positive pools were uniformly captured in the different environments.Conclusions/SignificanceObtained data highlighting the possible role of Cx. pipiens mosquito as the main vector for WNV and USUV in Northern Italy, and the possible involvement of Ae. albopictus mosquito in USUV cycle. The described mosquito-based surveillance could constitute the foundation for a public health alert system targeting mosquito borne arboviruses.
Highlights
West Nile virus (WNV) and Usutu virus (USUV) are mosquitoborne flaviviruses of the Japanese encephalitis antigenic complex [1]; these two viruses are phylogenetically closely related, as shown by nucleotide sequence data [2,3,4].Even if USUV ecology is less known than the WNV one, the two viruses seem to show biological cycle similarities: the principal vectors of WNV and USUV are largely ornithophilic mosquitoes, mainly of the genus Culex, wild birds are principal reservoirs of WNV and they are suspected of being of USUV, both viruses can be pathogenic for these animals [5,6,7,8]
Biomolecular analyses were performed on aliquots of 1,789 mosquito pools (Table 2) giving the subsequent results: 19 WNVpositive pools, 48 USUV-positive pools and 8 positive pools for both viruses (Figure 1, Figure 2)
The WNV was isolated from one pool of Cx. pipiens mosquito sampled in Montecchio municipality (Reggio Emilia province) on the August 26
Summary
West Nile virus (WNV) and Usutu virus (USUV) are mosquitoborne flaviviruses of the Japanese encephalitis antigenic complex [1]; these two viruses are phylogenetically closely related, as shown by nucleotide sequence data [2,3,4].Even if USUV ecology is less known than the WNV one, the two viruses seem to show biological cycle similarities: the principal vectors of WNV and USUV are largely ornithophilic mosquitoes, mainly of the genus Culex, wild birds are principal reservoirs of WNV and they are suspected of being of USUV, both viruses can be pathogenic for these animals [5,6,7,8]. West Nile virus (WNV) and Usutu virus (USUV) are mosquitoborne flaviviruses of the Japanese encephalitis antigenic complex [1]; these two viruses are phylogenetically closely related, as shown by nucleotide sequence data [2,3,4]. WNV can be transmitted occasionally by mosquitoes to vertebrates other than birds; these are considered dead-end host or seem to have only a minor role in the environmental maintenance of the virus. While the WNV risks for human health is well recognized, medical importance of USUV is not fully understood, but in summer 2009 USUV-related illness were reported in two immunecompromised patients in Emilia-Romagna region [14,15]. In recent years human diseases due to mosquito-borne viruses were increasingly reported in Emilia-Romagna region (Italy), from the chikungunya virus in 2007 to the West Nile virus (WNV) in 2008. An extensive entomological survey was performed in 2009 to establish the presence and distribution of mosquito arboviruses in this region, with particular reference to flaviviruses
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