Background: Due to the populationsââ?¬â?¢ susceptibility, DENV-4 introduction in 2010 led to the occurrence of explosive\nepidemics in the following years in Brazil. In 2011, DENV-4 was identified in Rio de Janeiro (RJ) and it was prevalent\nin 2012 and 2013. Here, we aimed to characterize clinical, epidemiological and laboratorial aspects of DENV-4 cases\nafter this serotype introduction in an endemic scenario.\nMethods: Dengue suspected cases (n = 3727) were received and analyzed from January 2011 to December 2013,\nduring outbreaks occurred in RJ, Brazil. Samples were submitted to virological, serological and molecular methods for\ncase confirmation. DENV-4 cases (n = 705) were characterized according to the type of infection, disease severity and,\nviremia levels and NS1 antigenemia were accessed. Representative strains were partial sequenced for genotyping.\nResults: DENV-4 was identified in 44.2% (705/1593) of dengue positive cases, virus isolated in 48.7% of the cases.\nAnti-DENV IgM was detected in 39.4% of the cases, however an increased detection was observed in cases with\nââ?°Â¥4 days of symptoms (57.0%). NS1 antigen was identified in 41.5% of DENV-4 cases however, after immune complexes\ndissociation, the detection significantly increased (87.6%). Females were more affected than males, so did children aged\n11ââ?¬â??15 years old. Primary cases were more frequently observed than secondary ones and most of them were classified\nas dengue. No differences on NS1 antigenemia and viraemia within the groups were observed. Despite the higher\nfrequency of severe disease on individuals >65 years old, no differences were observed among the groups and type of\ninfection. However, DENV-4 fatal cases were more frequent on secondary infections (57.1%). DENV-4 Genotype II was\nidentified with a probable origin from Venezuela and Colombia.\nConclusions: It has been shown that laboratorial diagnosis is still a reliable tool for the disease surveillance, detecting\nand confirming emerging epidemics. Despite the occurrence of secondary infections, most DENV-4 cases presented a\nmild disease. As RJ is endemic for dengue, high rates of secondary infections would be expected. Despite the existence\nof two genotypes, only Genotype II was identified in our study.
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