RESUMEN
The yellow fever virus (YFV) epidemic in Brazil is the largest in decades. The recent discovery of YFV in Brazilian Aedes species mosquitos highlights a need to monitor the risk of reestablishment of urban YFV transmission in the Americas. We use a suite of epidemiological, spatial, and genomic approaches to characterize YFV transmission. We show that the age and sex distribution of human cases is characteristic of sylvatic transmission. Analysis of YFV cases combined with genomes generated locally reveals an early phase of sylvatic YFV transmission and spatial expansion toward previously YFV-free areas, followed by a rise in viral spillover to humans in late 2016. Our results establish a framework for monitoring YFV transmission in real time that will contribute to a global strategy to eliminate future YFV epidemics.
Asunto(s)
Brotes de Enfermedades/prevención & control , Monitoreo Epidemiológico , Genómica/métodos , Fiebre Amarilla/prevención & control , Fiebre Amarilla/transmisión , Virus de la Fiebre Amarilla/aislamiento & purificación , Aedes/virología , Factores de Edad , Animales , Brasil/epidemiología , Brotes de Enfermedades/estadística & datos numéricos , Evolución Molecular , Humanos , Filogenia , Reacción en Cadena de la Polimerasa , Riesgo , Factores Sexuales , Análisis Espacio-Temporal , Fiebre Amarilla/epidemiología , Fiebre Amarilla/virología , Virus de la Fiebre Amarilla/clasificación , Virus de la Fiebre Amarilla/genéticaRESUMEN
Rapid geographic range expansions can have dramatic effects on the distribution of genetic diversity, both within and among populations. Based on field records collected over the past two decades in Western Europe, we report on the rapid geographic range expansion in Colletes hederae, a solitary bee species. To characterize how this expansion shaped the distribution of genetic diversity within and among populations, we performed a genetic analysis based on the sequencing of three nuclear loci (RNAp, CAD and WgL). We then simulated the evolution of DNA sequences under a spatially explicit model of coalescence to compare different hypotheses regarding the mode of colonization associated with this rapid expansion and to identify those that are most consistent with the observed molecular data. Our genetic analyses indicate that the range expansion was not associated with an important reduction in genetic diversity, even in the most recently colonized area in the United Kingdom. Moreover, little genetic differentiation was observed among populations. Our comparative analysis of simulated data sets indicates that the observed genetic data are more consistent with a demographic scenario involving relatively high migration rates than with a scenario based on a high reproduction rate associated with few migrants. In the light of these results, we discuss the factors that might have contributed to the rapid geographic range expansion of this pollen-specialist solitary bee species across Western Europe.