Análise molecular, espacial e temporal da transmissão de dengue no município de São José do Rio Preto-SP

Abstract

Dengue belongs to the Flavivirus genus and is the most common arboviral infection worldwide. It can be caused by four antigenically different serotypes (DENV 1-4). These serotypes are transmitted mainly by the bite of Aedes aegypti mosquitoes. The vector is widely associated with human activity and the influence of organized social space favors the interaction among vector, virus and man, making populated areas sources of dengue dispersion. In this study, we performed a molecular, spatial and temporal study of DENV transmission through positive samples of blood and infected mosquitoes captured in São José do Rio Preto/SP in a period of four years. Material and Methods: Serum samples of patients presenting dengue like symptoms and pools of mosquitoes had their viral RNA extracted and were tested by Multiplex- RT-PCR with Flavivirus generic primers based on non-structural protein (NS5) in the first round, followed by Nested assays with species-specific primers for the identification of DENV 1-3, yellow fever virus, Saint Louis encephalitis virus (SLEV) among others. Positive samples were analyzed spatially and phylogenetically. Results and Discussion: We analyzed 613 blood samples for four years: 199 in 2006, 94 in 2007, 313 in 2008 and 10 in 2009. The positivity was high in 2006 and 2007, with 106 and 51 infected patients, respectively. The major dengue serotype circulating during the 2006 and 2007 epidemics was DENV-3 and few cases of DENV-2, which is an indication of its recent introduction in the municipality. We also reported the first outbreak of SLEV in Brazil in 2006. Among DENV patients in 2008, only seven were infected by DENV-3 and 90 were infected by DENV-2, suggesting the reemergence of this serotype. We detected the circulation of DENV-1 in two Abstract xxv patients in 2008 and in four patients in 2009. Nearly 1200 mosquitoes were captured from December 2007 to March 2008. We have captured 814 Aedes aegypti mosquitoes, which were divided in 463 pools. Only 3.67% of them were positive for DENV-3 and DENV-2. Pools containing only male mosquitoes were positive for DENV, indicating the presence of transovarial transmission. We obtained sequences from 82 patients among 174 blood samples. We were able to geo-code 46 sequences. The alignment generated a 399-nucleotide long dataset with 134 taxa. The phylogenetic analysis indicated that all samples were of DENV-3 and related to strains circulating on the isle of Martinique in 2000 2001. Sixty DENV-3 from São José do Rio Preto formed a monophyletic group (lineage 1), closely related to the remaining 22 isolates (lineage 2). We assumed that these lineages appeared before 2006 in different occasions. The possibility of inferring the spatio-temporal dynamics from genetic data has been generally little explored, and it may shed light on DENV circulation. The use of both geographic and temporally structured phylogenetic data provided a detailed view on the spread of at least two dengue viral strains in a populated urban area.