Ecological and Genetic Analyses of the Complete Genomes of Culex Flavivirus Strains Isolated From <I>Culex tritaeniorhynchus</I> and <I>Culex pipiens</I> (Diptera: Culicidae) Group Mosquitoes

Abstract

Culex ßavivirus (CxFV) is an insect-speciÞc ßavivirus that was Þrst reported in 2007 in Japan. CxFV strains were isolated from Culex tritaeniorhynchus Giles and Culex pipiens L. group mosquitoes and genetically characterized in Toyama Prefecture, Japan, from 2004 to 2009, to reveal host speciÞcity, mode of transmission, and seasonal and geographical distribution. The minimum infection rate (MIR) of CxFV within Cx. tritaeniorhynchus populations was 0.3 and much lower than that within Cx. pipiens group (17.9). The complete genome sequences of 11 CxFV isolates (four from Cx. tritaeniorhynchus and seven from Cx. pipiens group) consisted of 10,835Ð10,837 nucleotides. When these 11 isolates and Þve reference strains (NIID-21-2 and Tokyo strains from Japan, Iowa07 and HOU24518 strains from the United States, H0901 strain from China) were compared, there were 95.2Ð99.2% nucleotide and 98.1Ð99.8% amino acid identities. Phylogenetic analysis showed that the 11 isolates were divided into four clusters. One cluster consisted of Þve isolates from Cx. pipiens group and Cx. tritaeniorhynchus from one site and their nucleotide sequences almost completely matched. One cluster consisted of an isolate with a unique sequence from a Cx. pipiens group mosquito captured in an aircraft from Taiwan, suggesting that it was introduced from abroad. CxFV strains were divided into several groups according to countries when nucleotide sequences of CxFV available in GenBank and 11 Toyama isolates were compared. These results suggest that CxFV is maintained in nature among Culex mosquitoes in a mosquito habitat-speciÞc but not a species-speciÞc manner.

Wide detection of Aedes flavivirus in north-eastern Italy – a European hotspot of emerging mosquito-borne diseases

“…These results support the hypothesis that the local ecological and climatic conditions may shape not only the abundance and distribution of mosquito populations (Roiz et al, 2010(Roiz et al, , 2011Trawinski & Mackay, 2010), but also their viral infection pattern (Newman et al, 2011;Calzolari et al, 2012b;Obara-Nagoya et al, 2013). The ecological and climatic conditions of the two study areas differ not only in climate, but also in the degree of anthropization, biodiveristy and land use.…”

“…Moreover, the prevalence of AeFV in Aedes albopictus in Trentino was higher than in Veneto and this result is supported by previous research carried out in 2008(Roiz et al, 2009, and it was also higher compared with the prevalence of ISFs detected in other northern Italian regions (e.g. Lombardia, Emilia-Romagna and Piemonte) (Roiz et al, 2009(Roiz et al, , 2012Calzolari et al, 2010a Calzolari et al, , b, 2012aCalzolari et al, , 2013aCerutti et al, 2012;Ravanini et al, 2012;Pautasso et al, 2013).These results support the hypothesis that the local ecological and climatic conditions may shape not only the abundance and distribution of mosquito populations (Roiz et al, 2010(Roiz et al, , 2011Trawinski & Mackay, 2010), but also their viral infection pattern (Newman et al, 2011;Calzolari et al, 2012b;Obara-Nagoya et al, 2013). The ecological and climatic conditions of the two study areas differ not only in climate, but also in the degree of anthropization, biodiveristy and land use.…”

“…It is thought that Aedes albopictus has most likely brought AeFV during its recent expansion from Japan to North America and Europe (Hawley et al, 1987;Rai, 1991;Benedict et al, 2007;Enserink, 2008;Bonizzoni et al, 2013). It has also been suggested that the nucleotide sequence is relatively well conserved because ISFs are not harmful to the mosquito host and because NS5 is not affected by host immunity (Obara-Nagoya et al, 2013). This result agrees with the discovery of high genome similarity between ISFs circulating in several European countries, demonstrating the widespread presence of different ISFs in Europe related to others isolated or detected worldwide and the high rate of gene flow amongst mosquito populations (Calzolari et al, 2012b;Cook et al, 2012;Obara-Nagoya et al, 2013).…”

“…It has also been suggested that the nucleotide sequence is relatively well conserved because ISFs are not harmful to the mosquito host and because NS5 is not affected by host immunity (Obara-Nagoya et al, 2013). This result agrees with the discovery of high genome similarity between ISFs circulating in several European countries, demonstrating the widespread presence of different ISFs in Europe related to others isolated or detected worldwide and the high rate of gene flow amongst mosquito populations (Calzolari et al, 2012b;Cook et al, 2012;Obara-Nagoya et al, 2013).In this study, we reported for the first time the detection of AeFV sequences from Culex pipiens from Veneto and Trentino. This result was unexpected because, at least to our knowledge, ISFs were thought to be maintained principally in a specific host genus, e.g.…”

Isolation of a Novel Insect-Specific Flavivirus fromCuliseta melanurain the Northeastern United States

“…tarsalis from the United States (Blitvich et al 2009 and Cx. tritaeniorhynchus from Japan (Obara-Nagoya et al 2013). CxFV appears to perpetuate in mosquito populations by vertical transmission, the passing of the virus from an infected female to her progeny (Saiyasombat et al 2011, Bolling et al 2012, and venereal transmission may also play a minor role in viral maintenance (Bolling et al 2012).…”