[First autochthonous cases, caused by the Dengue-3 serotype in Federal District, Brazil].

During the first four months of 2003, the survey laboratory of the Federal District (LACEN Laboratory of Virology), Brasília, Brazil, isolated ten strains of dengue virus serotype 3, five of them autochthonous, and the remaining ones from cases imported from Tocantins, Goias and Bahia States. The virus isolations were performed in C6/36 cell culture inoculated with total blood collected between the 1st and the 5th days after the onset of the symptoms. The age of the patients varied from 26 to 59 years old. The strains were typed as DEN-3 by indirect immunofluorescence assay using serotype-specific monoclonal antibodies. Viral RNAs were extracted from total blood using the trizol method. The nested RT-PCR method detected DNA products of 290 bp, confirming the serotype identifications. The introduction of DEN-3 in Brazil and especially in the Federal District represents a serious threat, since most people are susceptible to this serotype and many have already been infected by serotypes DEN-1 or DEN-2, thus increasing the risk of epidemic of more severe forms of the disease. The use of a fast and reliable method for continuous monitoring of the circulation of this serotype is of primary importance for the prevention and control of future epidemics.