Comparative sequence analyses of La Crosse virus strain isolated from patient with fatal encephalitis, Tennessee, USA.

We characterized a La Crosse virus (LACV) isolate from the brain of a child who died of encephalitis-associated complications in eastern Tennessee, USA, during summer 2012. We compared the isolate with LACV sequences from mosquitoes collected near the child's home just after his postmortem diagnosis. In addition, we conducted phylogenetic analyses of these and other sequences derived from LACV strains representing varied temporal, geographic, and ecologic origins. Consistent with historical findings, results of these analyses indicate that a limited range of LACV lineage I genotypes is associated with severe clinical outcomes.

SNP markers identify widely distributed clonal lineages of Phytophthora colocasiae in Vietnam, Hawaii and Hainan Island, China.

Taro (Colocasia esculenta) is an important food crop, and taro leaf blight caused by Phytophthora colocasiae can significantly affect production. Our objectives were to develop single nucleotide polymorphism (SNP) markers for P. colocasiae and characterize populations in Hawaii (HI), Vietnam (VN) and Hainan Island, China (HIC). In total, 379 isolates were analyzed for mating type and multilocus SNP profiles including 214 from HI, 97 from VN and 68 from HIC. A total of 1152 single nucleotide variant (SNV) sites were identified via restriction site-associated DNA (RAD) sequencing of two field isolates. Genotyping with 27 SNPs revealed 41 multilocus SNP genotypes grouped into seven clonal lineages containing 2-232 members. Three clonal lineages were shared among countries. In addition, five SNP markers had a low incidence of loss of heterozygosity (LOH) during asexual laboratory growth. For HI and VN, >95% of isolates were the A2 mating type. On HIC, isolates within single clonal lineages had A1, A2 and A0 (neuter) isolates. The implications for the wide dispersal of clonal lineages are discussed.

High degree of single nucleotide polymorphisms in California Culex pipiens (Diptera: Culicidae) sensu lato.

Resolution of systematic relationships among members of the Culex pipiens (L.) complex has important implications for public health as well as for studies on the evolution of sibling species. Currently held views contend that in California considerable genetic introgression occurs between Cx. pipiens and Cx. quinquefasciatus Say, and as such, these taxa behave as if they are a single species. Development of high throughput SNP genotyping tools for the analysis of Cx. pipiens complex population structure is therefore desirable. As a first step toward this goal, we sequenced 12 gene fragments from specimens collected in Marin and Fresno counties. On average, we found a higher single nucleotide polymorphism (SNP) density than any other mosquito species reported thus far. Coding regions contained significantly higher GC content (median 54.7%) than noncoding regions (42.4%; Wilcoxon rank sum test, P = 5.29 x 10(-5)). Differences in SNP allele frequencies observed between mosquitoes from Marin and Fresno counties indicated significant genetic divergence and suggest that SNP markers will be useful for future detailed population genetic studies of this group. The high density of SNPs highlights the difficulty in identifying species within the complex and may be associated with the large degree of phenotypic variation observed in this group of mosquitoes.

Culex pipiens sensu lato in California: a complex within a complex?

Culex pipiens sensu lato populations represent significant nuisance pests and vectors of West Nile virus in California. Despite multiple years of investigation, identifying, controlling and understanding the behaviors and associated "biologies" of the complex members still remain a challenge. Population structure cluster analysis using microsatellite markers revealed extensive population structuring, particularly in the central parts of the State, over and above what can be explained by the presence of Cx. pipiens, Cx. quinquefasciatus and their hybrids. Ace 2 gene sequencing provided evidence for the presence of Cx. p. molestus in multiple locations both above and below ground in California. Lack of congruence of male genitalia morphology (dorsal and ventral arms/dorsal arm of phalosome) and polymerase chain reaction diagnostic assay identifications coupled with considerable heterozygosity of pyrethroid resistance in time and space all suggest complex population structuring not adequately explained using current concepts.

Frequency of kdr and kdr-his Alleles in Stable Fly (Diptera: Muscidae) Populations From the United States, Costa Rica, France, and Thailand.

Anecdotal evidence of pyrethroid insecticide product failure for the control of stable fly [Stomoxys calcitrans (L.)] populations in the United States and worldwide prompted us to evaluate the frequency of knockdown resistance (kdr)-type polymorphisms within the voltage-sensitive sodium channel (Vssc) gene of field collected specimens from the United States, France, Costa Rica, and Thailand. The kdr-his allele (L1014H), associated with permethrin resistance, was detected in stable flies from the 10 states sampled in the United States, as well as from Costa Rica and France (Toulouse). Field collections of stable flies from California (Modesto) and New York (Cliffton Springs) exhibited reduced susceptibility upon exposure to a diagnostic permethrin concentration of 10× LC99, but survival did not appear to strictly associate with frequency of the kdr-his allele. This suggests that there are additional resistance mechanisms contributing to the phenotype in these states. The kdr allele (L1014F) was detected for the first time in stable flies originating in France and Thailand, and an improved, DNA-based diagnostic assay was developed and validated for use in future screens for kdr and kdr-his allele frequencies from field collections. The absence of kdr in United States and Costa Rica populations suggests that the allele is currently restricted to Europe and Asia.

Modeling a single season of Aedes albopictus populations based on host-seeking data in response to temperature and precipitation in eastern Tennessee.

In the southern Appalachia of the U.S., Aedes mosquitoes maintain and transmit La Crosse virus (LACV) which causes La Crosse encephalitis, a neuroinvasive disease of children. In response to mosquito outbreaks, communities organize prevention, detection, and response measures that are dependent on local characteristics of the mosquito population and the community. Knowing Ae. albopictus is an accessory vector of LACV and a nuisance biter, our objective was to build a system of ordinary differential equations to model dynamics in a single season using our data and readily available environmental variables that can reflect the abundance and activity of Ae. albopictus. Consequently, we built an Ae. albopictus single-season mathematical model for eastern Tennessee to fit our 2013 mosquito collection data in order to understand the population fluctuations. We included precipitation, temperature, and rate of change of temperature in the model because Aedes mosquitoes oviposit desiccant tolerant eggs with peak activity occurring over 26° C and those data are readily available and used frequently as forecast predictors. Our ordinary differential equation model accurately fits the data and facilitates predictions and better understanding of Ae. albopictus populations in southern Appalachia.