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 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

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

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

Population information for the <i>Aedes aegypti</i> samples analyzed.

<p>*Number of individuals collected.</p><p>Population information for the <i>Aedes aegypti</i> samples analyzed.</p

Genetic Diversity of Brazilian <i>Aedes aegypti</i>: Patterns following an Eradication Program

<div><p>Background</p><p><i>Aedes aegypti</i> is the most important vector of dengue fever in Brazil, where severe epidemics have recently taken place. <i>Ae. aegypti</i> in Brazil was the subject of an intense eradication program in the 1940s and 50s to control yellow fever. Brazil was the largest country declared free of this mosquito by the Pan-American Health Organization in 1958. Soon after relaxation of this program, <i>Ae. aegypti</i> reappeared in this country, and by the early 1980s dengue fever had been reported. The aim of this study is to analyze the present-day genetic patterns of <i>Ae. aegypti</i> populations in Brazil.</p><p>Methodology/Principal Findings</p><p>We studied the genetic variation in samples of 11 widely spread populations of <i>Ae. aegypti</i> in Brazil based on 12 well-established microsatellite loci. Our principal finding is that present-day Brazilian <i>Ae. aegypti</i> populations form two distinct groups, one in the northwest and one in the southeast of the country. These two groups have genetic affinities to northern South American countries and the Caribbean, respectively. This is consistent with what has been reported for other genetic markers such as mitochondrial DNA and allele frequencies at the insecticide resistance gene, <i>kdr</i>.</p><p>Conclusions/Significance</p><p>We conclude that the genetic patterns in present day populations of <i>Ae. aegypti</i> in Brazil are more consistent with a complete eradication of the species in the recent past followed by re-colonization, rather than the alternative possibility of expansion from residual pockets of refugia. At least two colonizations are likely to have taken place, one from northern South American countries (e.g., Venezuela) that founded the northwestern group, and one from the Caribbean that founded the southeastern group. The proposed source areas were never declared free of <i>Ae. aegypti</i>.</p></div

Factorial Correspondence analysis based on 12 microsatellite loci of <i>Ae. aegypti</i> populations from Brazil.

<p>Colors correspond to K = 2 cluster analysis displayed on <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0003167#pntd-0003167-g002" target="_blank">figure 2</a>.</p

Population pairwise F_ST^* values for <i>Ae. aegypti</i> populations studied.

<p>*Below diagonal, F_ST values without correction, all significantly different from zero. Above diagonal FreeNA corrected F_ST values.</p><p>Aracajú – ARA; Goiania – GO, Maceió – MA; Mossoró – MOS; Pau dos Ferros – PDF; Tucuruí – TU; Marabá – MAR; Natal – NAT; São Gonçalo – SG; Bolivar – BOL; Zúlia – ZUL; Houston – HOU; Coatzacoalcos – COA; Pijijiapan – PIJI; Dominica – DOM; Puerto Rico – PR; Miami – MIA; Cachoeiro 2008 – ES08; Cachoeiro 2012 – ES12; Jacobina – JAC.</p><p>Population pairwise F_ST^{<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0003167#nt102" target="_blank">*</a>} values for <i>Ae. aegypti</i> populations studied.</p

Collection sites for <i>Ae. aegypti</i> populations used in this study.

<p>Coloring indicates the two different clusters found on K = 2 STRUCTURE analysis (<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0003167#pntd-0003167-g002" target="_blank">Figure 2</a>).</p

MicrosatsforGenepop

MicrosatsforGenepo