» Ecology

Ana Maria Jansen-Franken
Laboratory of Biology of Trypanosomatids, Instituto Oswaldo Cruz/Fiocruz
The success of the Southern Cone initiative in eliminating the intradomiciliary vector transmission of Trypanosoma cruzi in Brazil resulted from the massive spraying campaign with the resulting eradication of the main vector: Triatoma infestans.
The prospect that the vacant niches resulting from the elimination of T. infestans could be occupied by species of wild triatomines, led to the maintenance of epidemiological surveillance being recognized as fundamental.
Although there is no way to carry out epidemiological surveillance without considering all the links in the transmission chain and the landscape where they occur, the absolute majority of epidemiological surveillance actions and projects are based on the survey and collection of triatomines at home and peridomicile, in addition, of course, to the monitoring of new cases of Chagas’ disease. However, it is important to remember that triatomine vectors acquire T. cruzi infection by feeding on their hosts and/or reservoirs, which may include a significant number of mammalian species. However, it must be remembered that T. cruzi is an eclectic parasite in terms of its hosts and habitats and is transmitted in well-established parasitic networks in all biomes of the country and that this is an aspect that must be included in sanitary surveillance actions.
The transmission cycle of T. cruzi in the wild is still an unsolved puzzle as it presents regional and temporal, macro and micro ecological peculiarities, which interfere in the interaction of this parasite with its hosts and vectors. The complexity of the transmission cycles of this parasite is evidenced by the recent outbreaks of Chagas’ disease that occurred in several regions of Brazil. These outbreaks occurred independently of the domiciliation of triatomines and have been attributed, even in some cases without empirical evidence, to the ingestion of food contaminated with the metacyclic infective forms derived from insects.
These outbreaks, as well as other unanswered questions, including the different conditions of the disease in different geographic regions, show that each epidemiological situation of American trypanosomiasis is unique in a certain space and time frame, therefore, generalizations of control measures run the risk of being ineffective.
Environmental changes, whether natural or not, result in the dispersion of animals and consequently of their parasites to new areas, creating a new epidemiological scenario. This is an especially important phenomenon with generalist parasites such as T. cruzi. Therefore, epidemiological surveillance must, obligatorily, consider in each target area, in addition to the triatomine fauna, the diversity of the local free-living, synanthropic, and domestic mammal fauna; the pattern of infection that will translate its competence as a reservoir; vegetation patterns, climate; alteration of the original habitat and alteration of the landscape; and, of course, the different sub-populations of the parasite that circulate in the area.
The study of the transmission of T. cruzi between its hosts and reservoirs involves the integration of several areas of knowledge. Only from a multidisciplinary approach can a correlation be established between the ecology of the landscape, the faunal survey, prevalence and incidence rates and, finally, an epidemiological risk assessment.
It is within this approach that we have studied the transmission of T. cruzi in the natural environment. Therefore, some aspects related to the transmission cycles of T. cruzi among its wild reservoirs are presented here.