Counts of dead birds sampled by three vector control agencies for FTA™ and/or RNASound™ card testing for West Nile virus, which were compared to parallel tissue testing (RT-PCR) at the UC Davis Arbovirus Research and Training Laboratory.

<p>Trial II, July-August 2013, California. Additional tissue testing (RT-PCR) by agencies is in parentheses.</p

Average cycle threshold (Ct) score differences, standard errors, and <i>P</i>-values for T-tests conducted on RT-PCR results for: oral samples on FTA™ cards, kidney tissue, and oral swab (American Crows) analyses from corvid species.

<p>Trial II, July-August 2013, California. Bolded test methods indicate the higher (therefore less viral RNA detected) scores in each pair. Ct scores were available for n = 41 of the 58 birds tested. (AMCR = American Crow; WESJ = Western Scrub-jay; YBMA = Yellow-billed Magpie).</p

Average cycle threshold (Ct) score differences, standard errors, and <i>P</i>-values for T-tests conducted on RT-PCR results from West Nile virus testing of dead corvids.

<p>Comparisons between: oral samples on FTA™ cards, kidney tissue, and oral swab (American crows) analyses. Trial I, June-August 2012, California. Underlined test methods indicate the higher (therefore less viral RNA detected) scores in each pair. Ct scores were available for n = 24 of the 55 birds tested.</p

Summary of West Nile virus test results for multiple bird species: oral samples on FTA™ cards and/or RNASound™ cards compared to one or more results from kidney tissue, oral swab, or brain tissue analyses (RT-PCR).

<p>Trial II, July-August 2013, California.</p

Summary of West Nile virus test results for dead corvids: oral samples on FTA™ cards, and parallel kidney tissue (RT-PCR).

<p>Trial I, June-August 2012, California. AMCR = American Crow; WESJ = Western Scrub-jay; YBMA = Yellow-billed Magpie.</p

Origin of the Dengue Fever Mosquito, <i>Aedes aegypti</i>, in California

<div><p>Dengue fever is among the most widespread vector-borne infectious diseases. The primary vector of dengue is the <i>Aedes aegypti</i> mosquito. <i>Ae. aegypti</i> is prevalent in the tropics and sub-tropics and is closely associated with human habitats outside its native range of Africa. While long established in the southeastern United States of America where dengue is re-emerging, breeding populations have never been reported from California until the summer of 2013. Using 12 highly variable microsatellite loci and a database of reference populations, we have determined that the likely source of the California introduction is the southeastern United States, ruling out introductions from abroad, from the geographically closer Arizona or northern Mexico populations, or an accidental release from a research laboratory. The power to identify the origin of new introductions of invasive vectors of human disease relies heavily on the availability of a panel of reference populations. Our work demonstrates the importance of generating extensive reference databases of genetically fingerprinted human-disease vector populations to aid public health efforts to prevent the introduction and spread of vector-borne diseases.</p></div

Genetic diversity of <i>Aedes aegypti</i> populations.

<p>H_o = observed heterozygosity; H_e = expected heterozygosity; AR = Allelic richness estimated by rarefaction (N = 30 genes).</p><p>*Pantropical = mean across populations from Asia and the Americas.</p><p>**Lab strains = mean across Hamburg, Rockefeller, and Liverpool laboratory strains provided by David Severson (University of Notre Dame, Indiana).</p

Genetic structure within pantropical populations of <i>Aedes aegypti</i>.

<p>STRUCTURE bar plots indicating relatedness of <i>Aedes aegypti</i> populations based on 12 microsatellite loci. Each vertical bar represents an individual. The height of each bar represents the probability of assignment to each of K optimal clusters (different colors) determined using the Delta K method. (<b>A</b>) North America and Asian populations (K = 2), and (<b>B</b>) North American populations (K = 3). (<b>C</b>) Map indicating the North American geographic locations sampled in this study. (<b>Δ</b>) California, (○) other locations in North America.</p

Individual and group mosquito genetic assignments.

<p>Percentage of individuals from Madera (<b>A</b>), Fresno (<b>B</b>), and San Mateo (<b>C</b>) counties assigned with the highest probability to each of the reference populations. (<b>D</b>) Scores calculated for each of the reference populations after group assignment of each of three California populations. Assignments were performed using Bayesian criteria for likelihood estimation with GENECLASS 2.0.</p

Multiple introductions of the dengue vector, <i>Aedes aegypti</i>, into California

<div><p>The yellow fever mosquito <i>Aedes aegypti</i> inhabits much of the tropical and subtropical world and is a primary vector of dengue, Zika, and chikungunya viruses. Breeding populations of <i>A</i>. <i>aegypti</i> were first reported in California (CA) in 2013. Initial genetic analyses using 12 microsatellites on collections from Northern CA in 2013 indicated the South Central US region as the likely source of the introduction. We expanded genetic analyses of CA <i>A</i>. <i>aegypti</i> by: (a) examining additional Northern CA samples and including samples from Southern CA, (b) including more southern US populations for comparison, and (c) genotyping a subset of samples at 15,698 SNPs. Major results are: (1) Northern and Southern CA populations are distinct. (2) Northern populations are more genetically diverse than Southern CA populations. (3) Northern and Southern CA groups were likely founded by two independent introductions which came from the South Central US and Southwest US/northern Mexico regions respectively. (4) Our genetic data suggest that the founding events giving rise to the Northern CA and Southern CA populations likely occurred before the populations were first recognized in 2013 and 2014, respectively. (5) A Northern CA population analyzed at multiple time-points (two years apart) is genetically stable, consistent with permanent <i>in situ</i> breeding. These results expand previous work on the origin of California <i>A</i>. <i>aegypti</i> with the novel finding that this species entered California on multiple occasions, likely some years before its initial detection. This work has implications for mosquito surveillance and vector control activities not only in California but also in other regions where the distribution of this invasive mosquito is expanding.</p></div