The biggest health problem, for which there is no preventive treatment, is dengue fever. The disease is widespread, and it is transmitted by the mosquito Aedes aegypti. In recent years, there have been massive outbreaks of dengue fever in regions of the states of Rio, São Paulo, and most recently, Mato Grosso do Sul. Typical syntomps include high fever, headache, muscular pain, nausea and vomit.
As there is no vaccine against dengue, the only advice that can be given is to avoid being bitten by the mosquito (easier said than done). The mosquito lives in places where there are pools of clean water (for instance, in discarded tyres).
To obtain information on other health problems, including malaria and yellow fever, you are advised to get in touch with a doctor.