Modifying the environment is a characteristic of the human species. With deforestation and the expansion of urban centers, diseases known in animals have begun to be described in humans. Science textbooks constitute an instrument of great importance in understanding this issue. This study evaluated the main science textbooks, recommended by the Brazilian Textbook Guide 2011, for the 6th grade of middle school, covering the parasite cycles and analyzing the vector/host relationships as well as man's participation as an inducer/victim. The final analysis showed that most textbooks link image and text, but the cycles are presented off-scale and there are gaps which hinder the understanding of reality. As regards the environmental question, none of the analyzed books presented human beings as an inducer of cycles, and only a few reported the lack of sanitation, urban infrastructure and environmental degradation as causes of disease.