The spatial and temporal scales of local dengue virus transmission in natural settings:a retrospective analysis

Background Dengue is a vector-borne disease caused by the dengue virus (DENV). Despite the crucial role of Aedes mosquitoes in DENV transmission, pure vector indices poorly correlate with human infections. Therefore there is great need for a better understanding of the spatial and temporal scales of DENV transmission between mosquitoes and humans. Here, we have systematically monitored the circulation of DENV in individual Aedes spp. mosquitoes and human patients from Caratinga, a dengue endemic city in the state of Minas Gerais, in Southeast Brazil. From these data, we have developed a novel stochastic point process pattern algorithm to identify the spatial and temporal association between DENV infected mosquitoes and human patients. Methods The algorithm comprises of: (i) parameterization of the variogram for the incidence of each DENV serotype in mosquitoes; (ii) identification of the spatial and temporal ranges and variances of DENV incidence in mosquitoes in the proximity of humans infected with dengue; and (iii) analysis of the association between a set of environmental variables and DENV incidence in mosquitoes in the proximity of humans infected with dengue using a spatio-temporal additive, geostatistical linear model. Results DENV serotypes 1 and 3 were the most common virus serotypes detected in both mosquitoes and humans. Using the data on each virus serotype separately, our spatio-temporal analyses indicated that infected humans were located in areas with the highest DENV incidence in mosquitoes, when incidence is calculated within 2.5–3 km and 50 days (credible interval 30–70 days) before onset of symptoms in humans. These measurements are in agreement with expected distances covered by mosquitoes and humans and the time for virus incubation. Finally, DENV incidence in mosquitoes found in the vicinity of infected humans correlated well with the low wind speed, higher air temperature and northerly winds that were more likely to favor vector survival and dispersal in Caratinga. Conclusions We have proposed a new way of modeling bivariate point pattern on the transmission of arthropod-borne pathogens between vector and host when the location of infection in the latter is known. This strategy avoids some of the strong and unrealistic assumptions made by other point-process models. Regarding virus transmission in Caratinga, our model showed a strong and significant association between high DENV incidence in mosquitoes and the onset of symptoms in humans at specific spatial and temporal windows. Together, our results indicate that vector surveillance must be a priority for dengue control. Nevertheless, localized vector control at distances lower than 2.5 km around premises with infected vectors in densely populated areas are not likely to be effective

Monitoramento do Dengue virus circulante em larvas e mosquitos adultos de Aedes aegypti

Exportado OPUSMade available in DSpace on 2019-08-14T07:57:31Z (GMT). No. of bitstreams: 1 disserta__o_ana__vers_o_final.pdf: 1925438 bytes, checksum: 201f670943764d3a9322cba22579e3dc (MD5) Previous issue date: 17O Dengue virus é o agente etiológico da dengue, a arbovirose mais prevalente no mundo, sendo, anualmente, notificados cerca de 50 milhões de casos. Os mosquitos vetores da dengue pertencem ao gênero Aedes, sendo a espécie Aedes aegypti, o principal vetor. Este trabalho busca o aprimoramento de técnicas de detecção do genoma de Dengue virus em larvas e mosquitos adultos a fim de otimizar os métodos de predição de epidemias que utilizam armadilhas para captura do vetor. Neste trabalho, a presença do genoma viral em mosquitos e larvas foi analisada por RT-PCR. As larvas e mosquitos adultos processados pertencem a um bairro da regional Noroeste de Belo Horizonte, MG, que apresenta os maiores índices de prevalência de dengue nos últimos anos, em Belo Horizonte (36% do total de casos notificados até 2006). Para a captura de ovos e mosquitos adultos foram utilizados quatro métodos de amostragem: Ovitrampa, BG-Trap®R, MosquiTRAPR e Aspirador de NasciR. Dos insetos coletados, 661 fêmeas, 372 machos e 28808 larvas foram macerados e submetidos à extração de RNA. A presença do genoma viral foi detectada por RT-PCR em 13,2% dos pools de larvas de Ae. Aegypti, em 16,6% dos pools de machos da BG-Trap® e em 20% dos pools de machos do Aspirador de Nasci. Para os pools de fêmeas analisados, foi encontrada a presença do genoma viral numa percentagem de 14,3% para a BG-Trap® e 16,6% para a MosquiTRAP. As técnicas moleculares utilizadas se mostraram eficientes, sendo a presença do genoma viral detectada em até 0,1 PFU. As armadilhas se mostraram eficientes na captura do vetor, sendo a MosquiTRAPR mais eficiente em coletas de fêmeas grávidas, capazes de transmitir o vírus. A metodologia é eficiente e pode ser empregada em programas de monitoramento para controle e prevenção da doença

Silent Circulation of the Saint Louis Encephalitis Virus among Humans and Equids, Southeast Brazil

Saint Louis encephalitis virus (SLEV) is a mosquito-borne flavivirus that occurs throughout the Americas, and is considered a public health threat. In Brazil, SLEV has been detected from human cases associated with dengue-like disease, but no neurological symptoms were reported. Furthermore, the epidemiology of SLEV in human populations is still poorly explored in the country. We reported serological and molecular detection of SLEV in a healthy population of equids and humans from rural areas in Southeast Brazil. A plaque reduction neutralization test was applied, and neutralizing antibodies were detected in 11 individuals (4.6%) and 60 horses (21.5%). A qPCR targeting the 5′UTR region and reverse transcription-PCR (RT-PCR) targeting the non-structural protein (NS5) gene were performed and three individuals tested positive in both assays. Subsequent phylogenetic analysis confirmed SLEV circulation and its findings suggest the occurrence of an asymptomatic or subclinical presence in human and animal cases, correlating with the risks for outbreaks and consequently burden of SLEV infections to public health. Preventive strategies should include improved surveillance in regions with a high probability of SLEV occurrence, improvement in diagnostic methods, and evaluation of exposure/risk factors that can favor SLEV emergence