Flavivirus susceptibility in Aedes aegypti.

To date, no polymerase chain reaction diagnostic technique exists to directly identify mammalian blood meals from mosquitoes by sized DNA fragments following agarose gel electrophoresis. We have developed a vertebrate-specific multiplexed primer set based on mitochondrial cytochrome b to identify the mammalian blood hosts of field-collected mosquitoes. Although designed for the study of African malaria vectors, the application of this tool is not restricted to this disease system. Validation of this diagnostic technique on dried anopheline and culicine field specimens collected in Zambia and Mali demonstrated that blood meals could be identified 2-7 months after collection. Time course experiments showed that host DNA was detectable in frozen mosquito abdomens 24-30 hours post-feeding. Additionally, multiple blood meals from different mammals could be detected in a single mosquito. This diagnostic assay will be a valuable tool for identifying the blood meals of field-collected mosquitoes where people and alternative mammal hosts are present.

Identification of mammalian blood meals in mosquitoes by a multiplexed polymerase chain reaction targeting cytochrome B.

Aedes aegypti from 24 collections in Mexico and the United States were challenged orally with dengue 2 virus JAM1409 (DEN-2 JAM1409). The vector competence (VC) of the populations ranged from 24% to 83%. Mosquito populations from the Yucatan exhibited greater VC than those from other areas of Mexico. The presence or absence of a midgut infection barrier (MIB) and a midgut escape barrier (MEB) was determined for mosquitoes in each population. The percentage of mosquitoes exhibiting an MIB ranged from 14% to 59%, and those exhibiting an MEB ranged from 4% to 43% in the collections. The MIB and MEB were not completely independent as determined by regression analysis. Midgut infection rates were dose dependent.

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Variation in vector competence for dengue 2 virus among 24 collections of Aedes aegypti from Mexico and the United States.

Mosquitoes, especially Aedes aegypti, are becoming important models for studying invasion biology. We characterized genetic variation at 12 microsatellite loci in 79 populations of Ae. aegypti from 30 countries in six continents, and used them to infer historical and modern patterns of invasion. Our results support the two subspecies Ae. aegypti formosus and Ae. aegypti aegypti as genetically distinct units. Ae. aegypti aegypti populations outside Africa are derived from ancestral African populations and are monophyletic. The two subspecies co-occur in both East Africa (Kenya) and West Africa (Senegal). In rural/forest settings (Rabai District of Kenya), the two subspecies remain genetically distinct, whereas in urban settings, they introgress freely. Populations outside Africa are highly genetically structured likely due to a combination of recent founder effects, discrete discontinuous habitats and low migration rates. Ancestral populations in sub-Saharan Africa are less genetically structured, as are the populations in Asia. Introduction of Ae. aegypti to the New World coinciding with trans-Atlantic shipping in the 16th to 18th centuries was followed by its introduction to Asia in the late 19th century from the New World or from now extinct populations in the Mediterranean Basin. Aedes mascarensis is a genetically distinct sister species to Ae. aegypti s.l. This study provides a reference database of genetic diversity that can be used to determine the likely origin of new introductions that occur regularly for this invasive species. The genetic uniqueness of many populations and regions has important implications for attempts to control Ae. aegypti, especially for the methods using genetic modification of populations.

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Global genetic diversity of Aedes aegypti

O texto discorre sobre a ecologia do Aedes aegypti, apontando questoes relevantes para a transmissao do dengue e para o seu controle. Indica temas a serem investigados na atual conjuntura epidemiologica da doenca no Brasil, procurando apontar algumas lacunas da compreensao da ecologia dos mosquitos, que poderiam contribuir para o aprimoramento e revisao dos programas de controle desses vetores no pais. Foi abordada a influencia das condicoes climaticas (temperatura, pluviosidade, altitude) no ciclo vital dos vetores, alem da adaptacao das especies a diferentes contextos ecologicos e sociais, de relevância para a vigilância entomologica. Tambem foram revistas as principais investigacoes sobre a domiciliacao, dispersao, repasto e reproducao dos vetores do dengue, alem da competencia e capacidade vetorial, chaves na compreensao da disseminacao da doenca e na organizacao das medidas de controle. Foi tambem abordada a resistencia do Aedes aegypti, cujo tema tem sido pesquisado em varias partes do mundo. Ressaltou-se a importância do monitoramento sistematico do tratamento quimico durante as acoes de campo. Foram apresentadas de forma resumida, as alternativas mais comumente utilizadas no controle fisico, quimico e biologico pelos programas de controle de Aedes aegypti no pais.

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Vigilância entomológica e controle de vetores do dengue

A population genetic analysis of gene flow was conducted among 10 Aedes aegypti collections from seven cities along the northeastern coast of Mexico. Four collections were made from Monterrey to examine local patterns of gene flow. Markers included 60 random amplified polymorphic DNA (RAPD) loci amplified by the polymerase chain reaction and single strand conformation polymorphism analysis of variation in a 387-basepair region of the NADH dehydrogenase subunit 4 from the mitochondrial DNA (mtDNA). Seven mitochondrial haplotypes were detected and phylogenetic analysis identified two well-supported clades. Regression analysis of geographic distances and pairwise FST estimated from RAPD markers indicated that populations are isolated by distance and that free gene flow occurs among collections within 90-250 km. Isolation by distance was not detected using mtDNA haplotypes. The Nuevo Laredo collection had unique RAPD and mtDNA haplotype frequencies and reduced heterozygosity suggesting that few mosquitoes established this population.

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N Gorrochotegui-Escalante

Papers

Genetic isolation by distance among Aedes aegypti populations along the northeastern coast of Mexico.