The WHO states that malaria and yellow fever are present in Brazil, but there have been no cases in the Belém urban area for many decades. If you are planning on a jungle vacation upriver, malaria prophylaxis may be wise. Also, the Amazon has many unusual foods, so tourists sometimes experience gastric problems - most tourists stick to bottled or filtered water. Belém is not a high risk city, but there are numerous pickpockets, so it is unwise to walk the streets with jewelry or visible cameras. Find below some links related to heath and safety in Brazil.

Australian Department of Foreign Affairs and Trade

Foreign & Commonwealth Office Travel Advice

Travel Report for Brazil

U.S. Department of State - Brazil

World Health Organization - Brazil