1,721,208 research outputs found
Air travel is associated with intracontinental spread of dengue virus serotypes 1-3 in Brazil.
Full text linkDengue virus and its four serotypes (DENV-1 to DENV-4) infect 390 million people and are implicated in at least 25,000 deaths annually, with the largest disease burden in tropical and subtropical regions. We investigated the spatial dynamics of DENV-1, DENV-2 and DENV-3 in Brazil by applying a statistical framework to complete genome sequences. For all three serotypes, we estimated that the introduction of new lineages occurred within 7 to 10-year intervals. New lineages were most likely to be imported from the Caribbean region to the North and Northeast regions of Brazil, and then to disperse at a rate of approximately 0.5 km/day. Joint statistical analysis of evolutionary, epidemiological and ecological data indicates that aerial transportation of humans and/or vector mosquitoes, rather than Aedes aegypti infestation rates or geographical distances, determine dengue virus spread in Brazil
Multi-locus genotyping reveals established endemicity of a geographically distinct Plasmodium vivax population in Mauritania, West Africa
Full text linkBackground
Plasmodium vivax has been recently discovered as a significant cause of malaria in Mauritania, although very rare elsewhere in West Africa. It has not been known if this is a recently introduced or locally remnant parasite population, nor whether the genetic structure reflects epidemic or endemic transmission.
Methodology/Principal findings
To investigate the P. vivax population genetic structure in Mauritania and compare with populations previously analysed elsewhere, multi-locus genotyping was undertaken on 100 clinical isolates, using a genome-wide panel of 38 single nucleotide polymorphisms (SNPs), plus seven SNPs in drug resistance genes. The Mauritanian P. vivax population is shown to be genetically diverse and divergent from populations elsewhere, indicated consistently by genetic distance matrix analysis, principal components analyses, and fixation indices. Only one isolate had a genotype clearly indicating recent importation, from a southeast Asian source. There was no linkage disequilibrium in the local parasite population, and only a small number of infections appeared to be closely genetically related, indicating that there is ongoing genetic recombination consistent with endemic transmission. The P. vivax diversity in a remote mining town was similar to that in the capital Nouakchott, with no indication of local substructure or of epidemic population structure. Drug resistance alleles were virtually absent in Mauritania, in contrast with P. vivax in other areas of the world.
Conclusions/Significance
The molecular epidemiology indicates that there is long-standing endemic transmission that will be very challenging to eliminate. The virtual absence of drug resistance alleles suggests that most infections have been untreated, and that this endemic infection has been more neglected in comparison to P. vivax elsewhere
Introducing the TrypanoGEN biobank: A valuable resource for the elimination of human African trypanosomiasis.
Full text linkNo abstract available
Automated phenotyping of mosquito larvae enables high-throughput screening for novel larvicides and offers potential for smartphone-based detection of larval insecticide resistance
Full text linkPyrethroid-impregnated nets have contributed significantly to halving the burden of malaria but resistance threatens their future efficacy and the pipeline of new insecticides is short. Here we report that an invertebrate automated phenotyping platform (INVAPP), combined with the algorithm Paragon, provides a robust system for measuring larval motility in Anopheles gambiae (and An. coluzzi) as well as Aedes aegypti with the capacity for high-throughput screening for new larvicides. By this means, we reliably quantified both time- and concentration-dependent actions of chemical insecticides faster than using the WHO standard larval assay. We illustrate the effectiveness of the system using an established larvicide (temephos) and demonstrate its capacity for library-scale chemical screening using the Medicines for Malaria Venture (MMV) Pathogen Box library. As a proof-of-principle, this library screen identified a compound, subsequently confirmed to be tolfenpyrad, as an effective larvicide. We have also used the INVAPP / Paragon system to compare responses in larvae derived from WHO classified deltamethrin resistant and sensitive mosquitoes. We show how this approach to monitoring larval response to insecticides can be adapted for use with a smartphone camera application and therefore has potential for further development as a simple portable field-assay with associated real-time, geo-located information to identify hotspots
Evolution and spread of Venezuelan equine encephalitis complex alphavirus in the Americas.
Full text linkVenezuelan equine encephalitis (VEE) complex alphaviruses are important re-emerging arboviruses that cause life-threatening disease in equids during epizootics as well as spillover human infections. We conducted a comprehensive analysis of VEE complex alphaviruses by sequencing the genomes of 94 strains and performing phylogenetic analyses of 130 isolates using complete open reading frames for the nonstructural and structural polyproteins. Our analyses confirmed purifying selection as a major mechanism influencing the evolution of these viruses as well as a confounding factor in molecular clock dating of ancestors. Times to most recent common ancestors (tMRCAs) could be robustly estimated only for the more recently diverged subtypes; the tMRCA of the ID/IAB/IC/II and IE clades of VEE virus (VEEV) were estimated at ca. 149-973 years ago. Evolution of the IE subtype has been characterized by a significant evolutionary shift from the rest of the VEEV complex, with an increase in structural protein substitutions that are unique to this group, possibly reflecting adaptation to its unique enzootic mosquito vector Culex (Melanoconion) taeniopus. Our inferred tree topologies suggest that VEEV is maintained primarily in situ, with only occasional spread to neighboring countries, probably reflecting the limited mobility of rodent hosts and mosquito vectors
Population genomics of the Asian tiger mosquito, Aedes albopictus. Insights into the recent worldwide invasion
Full text linkAedes albopictus, the “Asian tiger mosquito,” is an aggressive biting mosquito native to Asia that has colonized all continents except Antarctica during the last ~30–40 years. The species is of great public health concern as it can transmit at least 26 arboviruses, including dengue, chikungunya, and Zika viruses. In this study, using double- digest Restriction site-Associated DNA (ddRAD) sequencing, we developed a panel of ~58,000 single nucleotide polymorphisms (SNPs) based on 20 worldwide Ae. albopic-tus populations representing both the invasive and the native range. We used this genomic- based approach to study the genetic structure and the differentiation of Ae. albopictus populations and to understand origin(s) and dynamics of the recent inva-sions. Our analyses indicated the existence of two major genetically differentiated population clusters, each one including both native and invasive populations. The de-tection of additional genetic structure within each major cluster supports that these SNPs can detect differentiation at a global and local scale, while the similar levels of genomic diversity between native and invasive range populations support the scenario of multiple invasions or colonization by a large number of propagules. Finally, our re-sults revealed the possible source(s) of the recent invasion in Americas, Europe, and Africa, a finding with important implications for vector- control strategies
Speciazione incipiente in Anopheles gambiae s.s.?
No full textLe zanzare appartenenti al complesso Anopheles gambiae sono i principali vettori di malaria in Africa, continente dove si verificano il 90% dei casi di malaria al mondo. Originariamente considerata un'unica specie, A. gambiae è stata successivamente suddivisa in sei specie distinte in base a studi sulla resistenza agli insetticidi ed analisi dei polimorfismi da inversioni cromosomiche. Tra queste, A. gambiae ed A. arabiensis sono i due vettori di malaria più importanti per la loro stretta associazione con habitat antropizzati, la loro marcata antropofilia, e la loro efficienza nel trasmettere il parassita malarico. A partire dagli anni ottanta una serie di studi sulla distribuzione dei polimorfismi cromosomici in popolazioni di A. gambiae s.s. in Africa orientale ha messo in luce una discontinuità genetica ed ecologica ali' interno di questa specie. Su tale base è stata proposta l'esistenza di un complesso di unità tassonomiche distinte in A. gambiae s.s., definite "forme cromosomiche" ed identificate con i termini non-Linneani di
Savanna, Mopti, Bamako, Foreste Bissau. In collaborazione con Jeff Powell (Yale University) e Mario Coluzzi (Università di Roma "La Sapienza'") abbiamo iniziato un studio molecolare ad
ampia scala geografica di diverse popolazioni di A. gambiae s.s. per investigare livelli e moduli di variabilità in regioni di DNA nucleare e mitocondriale per verificare l'esistenza di taxa criptici all'interno della specie. Abbiamo sequenziato individui appartenenti a tre delle forme più comuni (Savanna, Mopti, e Bamako) provenienti sia da popolazioni allopatriche che simpatriche.
Un'analisi di circa 74 kb di DNA in regioni ad elevato tasso evolutivo non ha rivelato nessuna differenza fissata in modo alternativo tra le tre forme cromosomiche, nonostante l'elevato livello di polimorfismo presente nelle regioni analizzate. A differenza dello scarso differenziamento trovato in queste regioni, l'ITS (Internai Tanscribed Spacer) nel cluster del DNA ribosomale (rDNA) presenta una serie di sostituzioni alternative che identificano individui con cariotipi diversi. Per questa regione dell'rDNA abbiamo sequenziato 130 individui con cariotipi distinti provenienti da popolazioni dell'Africa orientale ed occidentale. Questo studio ha messo in evidenza l'esistenza di due tipi principali di varianti rDNA (Tipo I e Tipo II). Tali varianti esistono sia in condizioni di simpatria che di allopatria con livelli praticamente inesistenti di flusso. All'interno di uno dei due tipi di rDNA sono state inoltre evidenziate delle varianti geografiche. A differenza di studi precedenti basati su analisi di microsatelliti e DNA mitocondriale, i risultati ottenuti in questo studio con l'rDNA evidenziano un flusso genico ridotto tra le popolazioni di A. gambia e e avvallano l'ipotesi dell'esistenza di taxa criptici in A. gambiae s.s., sebbene la delimitazione genetica di tali unità non coincida completamente con quella fornita dalle inversioni cromosomiche. Inoltre verranno discussi lo stato tassonomico di queste forme ed i problemi connessi con un'eventuale assegnazione del rango di specie sulla base di un numero limitato di sostituzioni nucleotidiche
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
GENE FLOW IN CAVE ARTHROPODS: A QUALITATIVE AND QUANTITATIVE APPROACH
No full textSlatkin\u27s method (1981) for analyzing gene flow levels is applied to eleven species of cave arthropods. This provides insights into the strength of gene flow as a force affecting the evolution of cave organisms, while serving as a test of Slatkin\u27s method. The results show that patterns of gene flow are consistent with the dispersal abilities and the ecological requirements of each species. Troglobites in general have lower gene flow values than troglophiles or trogloxenes. However, the geology of the area, its vegetation profile, and the geographic distance among the populations considered are also important in determining the gene flow levels. Gene flow patterns in three cave species, Ptomaphagus hirtus, Neaphaenops tellkampfii tellkampfii and Hadenoecus subterraneus , are compared in detail. These species inhabit the same highly interconnected karst area in south‐central Kentucky but differ in their ecological requirements. The results suggest that gene flow levels are more dependent upon the intrinsic characteristics of each species than upon the availability of routes for dispersal. Overall estimates of gene flow were coupled with a more detailed population‐structure analysis in four terrestrial cave arthropods: Speonomus delarouzeei, Hadenoecus cumberlandicus, Hadenoecus subterraneus and Euhadenoecus puteanus . The results stress the need for this type of analysis for subdivided species, in which estimates of the average gene flow can produce misleading results. Moreover, they show how these types of measures are more relevant in describing historical patterns of gene exchange than in indicating current levels of gene flow
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