Genetic and phenotypic differences between isolates of Murray Valley encephalitis virus in Western Australia, 1972-2003

Murray Valley encephalitis virus (MVEV) is a medically important mosquito-borne flavivirus found in Australia and Papua New Guinea (PNG). Partial envelope gene nucleotide sequences of 28 isolates of MVEV from Western Australia (WA) between 1972 and 2003 were aligned and compared phylogenetically with the prototype MVE-1-51 from Victoria in 1951 and isolates from northern Queensland and PNG. Monoclonal antibody-binding patterns were also investigated. Results showed that the majority of isolates of MVEV from widely disparate locations in WA were genetically and phenotypically homogeneous. Furthermore, isolates of MVEV from WA and northern Queensland were almost identical, confirming results from earlier studies. Recent isolates of MVEV from Western Province in PNG were more similar to Australian isolates of MVEV than to isolates from PNG in 1956 and 1966, providing further evidence for the movement of flaviviruses between PNG and Australia. Additional representatives of a unique variant of MVEV (OR156) from Kununurra in the northeast Kimberley region of WA were also detected. This suggests that the OR156 lineage is still intermittently active but may be restricted to a small geographic area in northern WA, possibly due to altered biological characteristics

Population genetic structure of the Culex pipiens (Diptera: Culicidae) complex, vectors of West Nile virus, in five habitats

Background: The Culex pipiens complex consists of several morphologically similar, closely related species. In the United States, Cx. pipiens L. is distributed North of 39° latitude, while Cx. quinquefasciatus Say occurs South of 36° latitude; a hybrid zone occurs between these two latitudes including in the Central Valley of California. Members of the Cx. pipiens complex and their hybrids are vectors for West Nile virus (WNv). Hybrid offspring of Cx. pipiens and Cx. quinquefasciatus have been found to have enhanced transmission rates of WNv over those of pure populations of each species. We investigated whether hybrids of Cx. pipiens and Cx. quinquefasciatus occurred more frequently in any of five habitats which were dairies, rural, suburban, and urban areas, and wetlands. In addition, the proportion of alleles unique to Cx. quinquefasciatus and Cx. pipiens found in each habitat-associated population were determined. Methods: Amplified fragment length polymorphism (AFLP) markers were used to compare the population structure of the Cx. pipiens complex from each habitat to geographically distant populations considered pure Cx. pipiens and Cx. quinquefasciatus. Structure analyses were used to assign individuals to either Cx. pipiens, Cx. quinquefasciatus, or hybrids of the Cx. pipiens complex. The ancestry of hybrids (F1, F2, or backcrossed) in relation to the two parent populations was estimated for each Central Valley population. Loci unique to the pure Cx. pipiens population and the pure Cx. quinquefasciatus population were determined. The proportion of loci unique to Cx. pipiens and Cx. quinquefasciatus populations were subsequently determined for each population from the five Merced habitats and from the Oroville California population. The unique loci found in Merced populations and not in Cx. pipiens or Cx. quinquefasciatus were also determined. A principal components analysis was run, as was an analysis to determine loci under putative selection. Results: The Structure Harvester analysis found K = 3, and the Culex pipiens complex mosquitoes formed a genetic cluster distinct from Cx. quinquefasciatus and Cx. pipiens. Individuals collected from each habitat were nearly all hybrids. However, Cx. pipiens complex collected near dairies had more individuals categorized as Cx. pipiens than collections from the other habitats. None of the mosquitoes collected in Merced or Oroville were considered pure Cx. quinquefasciatus. Significant genetic divergence was detected among the Cx. pipiens complex from the five habitats in Merced; Cx. pipiens complex mosquitoes from dairies were divergent from the urban and suburban populations. New Hybrids analysis found that individuals from all five Merced habitat-associated populations and the population from Oroville were primarily categorized as hybrids backcrossed to the Cx. pipiens population. Finally, all five habitat-associated populations shared more alleles with Cx. pipiens than with Cx. quinquefasciatus, even though the pure Cx. quinquefasciatus population was more geographically proximate to Merced. Results from the principal component analysis, and the occurrence of several unique loci in Merced populations, suggest that Cx. pipiens molestus may also occur in the habitats sampled. Conclusions: Nearly all mosquitoes in the five habitats in Merced in the Central Valley of California area were hybrids of Cx. pipiens and Cx. quinquefasciatus, consisting of hybrids backcrossed to Cx. pipiens. Habitat-associated mosquitoes collected near dairies had more individuals consisting of pure Cx. pipiens, and no mosquitoes from Merced or Oroville CA classified as pure Cx. quinquefasciatus. The genetic distances among Cx. pipiens and Cx. quinquefasciatus, and hybrid populations agree with previous studies using other molecular markers. Cx. pipiens hybrids in Merced shared more alleles with Cx. pipiens than Cx. quinquefasciatus which was unexpected, since Merced is geographically closer to the northern limit of Cx. quinquefasciatus distribution. Culex pipiens molestus may occur in more habitats in the Central Valley than previously suspected, which warrants further investigation. Future studies could investigate the vector competence of hybrids backcrossed to either Cx. pipiens or Cx. quinquefasciatus parent for their ability to transmit West Nile virus.Science, Faculty ofOther UBCNon UBCMicrobiology and Immunology, Department ofReviewedFacult

High genetic diversity in the Culex pipiens complex from a West Nile Virus epidemic area in Southern Europe

Background The Culex pipiens complex includes the most widespread mosquito species in the world. Cx. pipiens is the primary vector of the West Nile Virus (WNV) in Europe and North America. Cases of WNV have been recorded in Italy since 1998. In particular, wet areas along the Po River are considered some of the most WNV affected areas in Italy. Here, we analyzed the genetic structure of ten Cx. pipiens populations collected in the last part of the Po River including the Delta area. Methods We assessed the genetic variability of two mitochondrial markers, cytochrome oxidase 1 (COI) and 2 (COII), for a total of 1200 bp, and one nuclear marker, a fragment of acetylcholinesterase-2 (ace-2), 502 bp long. The effect of the landscape features was evaluated comparing haplotype and nucleotide diversity with the landscape composition. Results The analysis showed a high genetic diversity in both COI and COII gene fragments mainly shared by the populations in the Delta area. The COI-COII network showed that the set of haplotypes found was grouped into three main supported lineages with the higher genetic variability gathered in two of the three lineages. By contrast, ace-2 fragment did not show the same differentiation, displaying alleles grouped in a single clade. Finally, a positive correlation between mitochondrial diversity and natural wetland areas was found. Conclusions The high mitochondrial genetic diversity found in Cx. pipiens populations from the Po River Delta contrasts with the low variability of inland populations. The different patterns of genetic diversity found comparing mitochondrial and nuclear markers could be explained by factors such as differences in effective population size between markers, sex biased dispersal or lower fitness of dispersing females. Moreover, the correlation between genetic diversity and wetland areas is consistent with ecosystem stability and lack of insecticide pressure characteristic of this habitat. The mtDNA polymorphism found in the Po River Delta is even more interesting due to possible linkages between the mitochondrial lineages and different biting behaviors of the mosquitoes influencing their vector ability of arboviral infections