The increasing use of Social Networks to share personal information has opened many resources to analyze the behaviour of one city, state or country. Topics related to politics, science, health alarms and others are shared by users everyday to monitor an prevent events. Natural Language Processing is the tool to analyze this text and get some insight using Machine Learning Techniques. In this work, Twitter is analyzed to detect social events because users are considered sensors. The analysis is performed over Brazilian tweets to detect dengue. The results show the utility of the proposal to recognize dengue epidemics in the Brazilian territory.