Epidemiological and genetic aspects of the largest dengue outbreak recorded in 2015 in Southeastern Brazil

Dengue virus, the etiological agent of dengue fever (DF) occurs in four genetically distinct serotypes (DENV1-4), being transmitted by female Aedes mosquitoes. DF incidence is increasing in Brazil, following vector dispersal, proliferation and DENV serotypes introduction, co-circulation and substitution. Medium- and small-sized cities in Sao Paulo State, such as Marilia (Midwest region), have been affected by huge epidemics. To understand the evolution of DENV epidemics in medium-sized cities, in this study a historical data on DENV incidence (2000-2015) in Marilia, was evaluated. Previous studies disclosed regional and specific DF outcomes associated with 2007 outbreak in that city, when co-circulating DENV1 and DENV3 presented different hematological profiles. In this study, characteristics of 2007 DENV epidemics were compared to the epidemiological, hematological and demographic outlines of the major outbreak of DENV1 in Marilia in 2015. DENV1 genetic diversity was assessed through capsid and pre-membrane junction encoding gene (CprM) sequencing. The results revealed circulation of DENV1 serotype from 2007 to 2015, with epidemics occurring every three-years until 2013 and then, increasing yearly. There were significant differences in hematological profiles of DENV1 patients between 2015 and 2007. CprM showed DENV1 genetic variability in 2015, contrasting with the unique sequence pattern in 2007. These results reinforce the regional and temporal characteristics of DENV epidemics that need local public health research to improve care for people and to limit the spread of new serotypes/genotypes to uninfected areas.