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Parasitic protozoa are important agents of human and veterinary diseases, which are widely distributed throughout the world. The parasite Trypanosoma cruzi, which is the causal agent of the human disease known as Chagas disease, affects approximately 8 million people and causes more than 14,000 deaths per year in Latin America. It is estimated that in Brazil there are around 2 million individuals infected . T. cruzi has a complex life cycle involving both vertebrate and invertebrate hosts in three well-defined developmental stages: (1) amastigotes, which are the proliferative forms found inside the vertebrate host cells; (2) epimastigotes, which are the proliferative forms found in the intestine of the invertebrate host; and (3) trypomastigotes, which are highly infective and originate from the amastigotes at the end of the intracellular cycle following their release into the intercellular space and into bloodstream . Trypomastigotes also arise from epimastigotes in the posterior regions of the digestive tract of the invertebrate host .
The present work aims to use a cell biologic approach to create multimedia materials that present basic aspects of the life cycle of T. cruzi and the morphology of its various developmental stages, as well as some biological processes such a division, motility, and endocytic activity.
The current teaching method is based upon formal lectures using classic material with little emphasis on the use of three-dimensional (3D) animation models. In this report, we present new instructional material with modern schemes and dynamic models that include 3D animations (Box 1). These educational tools will be useful for a broad audience, which includes students in face-to-face and distance education, teachers, researchers, and any member of the general public that are interested in parasites. As an instructional tool, the animations are more effective than the static graphics for teaching dynamic events . Studies in biology courses have shown that animations lead to increased student understanding and retention of cell biology information .
The 3D models and animations were produced by designers working at the CECIERJ Foundation (Fundação Centro de Ciências e Educação Superior a Distância do Estado do Rio de Janeiro - CEDERJ Consortium).
Our analysis is based on information obtained by our group in the last 20 years using video microscopy and light microscopy as well as scanning and transmission electron microscopy, which show various aspects of the structural organization of the protozoan and its interaction with host cells. Our analysis also used information obtained by different research groups. All animations and images were produced using software such as 3ds Max, Maya, Poser, and Flash.
During its life cycle, T. cruzi infects both invertebrate and vertebrate hosts. Figure 1 shows a general view of its life cycle of the basic aspects of the life cycle of T. cruzi in the human host (video: http://www.imbebb.org.br/conteudo.asp?idsecao=242) and in the triatomine insect (video: http://www.imbebb.org.br/conteudo.asp?idsecao=243).
On the basis of several images obtained by scanning and transmission electron microscopy, we made 3D figures that illustrate the general shape of the various developmental stages of T. cruzi as well as the presence and distribution of structures and organelles, as shown in Figures 2–4.4. A more detailed 3D animation of the ultrastructure of each developmental stage is shown in the videos found at http://www.imbebb.org.br/conteudo.asp?idsecao=253, http://www.imbebb.org.br/conteudo.asp?idsecao=252, and http://www.imbebb.org.br/conteudo.asp?idsecao=251.
We analyzed some of the dynamic processes, which take place in the T. cruzi cell cycle as (a) cell division (Figure 5 and http://www.imbebb.org.br/conteudo.asp?idsecao=250), (b) the highly polarized endocytic activity where the epimastigote forms uptake macromolecules from the medium as previously discussed in a recent review  (Figure 6 and http://www.imbebb.org.br/conteudo.asp?idsecao=249), and (c) the structural organization of the paraflagellar rod (PFR), which is a structure closely associated to the axoneme and a component of the flagellum of most of the trypanosomatids , . On the basis of the images obtained using atomic force microscopy (AFM) and transmission electron microscopy of freeze-fractured and deep-etched cells, we were able to propose a model for the PFR . A schematic motility is represented as a 3D hypothesis of the PFR (Figure 7 and video: http://www.imbebb.org.br/conteudo.asp?idsecao=248).
As part of the life cycle, the infective trypomastigote and amastigote forms of T. cruzi interact with different types of cells in the mammalian hosts, such as macrophages, muscle cells, epithelial cells, and neurons. This interaction has been studied in some detail in cell culture (both phagocytic and non-professional phagocytic cells). Figures 9–1111 and the next three videos illustrate the macrophage interactions with the non-infective epimastigotes as well as the infective amastigote and trypomastigote forms. For epimastigotes, the destruction of the intravacuolar parasite occurs (Figure 9, video: http://www.imbebb.org.br/conteudo.asp?idsecao=247). In trypomastigotes, fusion of the lysosomes with the parasitophorous vacuole (PV) occurs even during gradual transformation of trypomastigotes into amastigotes (Figure 10, video: http://www.imbebb.org.br/conteudo.asp?idsecao=246). A similar process occurs when amastigotes infect host cells (Figure 11, video: http://www.imbebb.org.br/conteudo.asp?idsecao=245). Figure 12 and the video at http://www.imbebb.org.br/conteudo.asp?idsecao=244 show the process of infection in heart muscle cells, where the intracellular cycle resembles that described for macrophages.
Taken together, the 3D schematics shown in Figures 9–1111 and the dynamic 3D videos of interaction between the forms of T. cruzi and macrophage cells allow a better visualization of the various developmental stages of T. cruzi, including dynamic cellular processes as well as the interaction of the protozoan with vertebrate and invertebrate hosts. The multimedia materials described herein will present a comprehensive view of the protozoan life cycle to students. These materials also offer dynamic models that improve our understanding of some important biological processes.
This work has been partially supported by FAPERJ. The authors would like to thank Celso Sant'Anna, Gustavo Rocha, Kildare Miranda, Danielle Cavalcanti, Tecia Maria Ulisses de Carvalho, Rodrigo Leite, Marcelo Xavier and Ricardo Amaral for their support during the development of this work.