versión impresa ISSN 0365-9402
Bol. chil. parasitol. v.55 n.1-2 Santiago ene. 2000
Natural reservoirs of Trypanosoma cruzi
In general, reservoirs of Trypanosoma cruzi are those mammals, included man domestic, synanthropic and wild which present natural infection by the parasite. Reservoirs have an important participation in the maintenance and interaction of domestic and wild cycles of American trypanosomiasis.
Though man is the unquestionable most domestic reservoir, dog and cat, chiefly the first both with an average life span of seven years play a significant role in the dynamics of T. cruzi transmission in human environment. Moreover, an important number of domestic and synanthropic mammals has been found naturally infected in practically all the countries of the American Continent, with the exception of Canada. Among these are goat, sheep, alpaca, pig, rabbit, guinea pig, rat and mouse.
Habitually the proportion of infected reservoirs is variable, according to the local epidemiological situation, depending its magnitude on the density and rates of infected triatomines in a houselhold, section or geographic unit. In general, T. cruzi circulation in the cycle is rather dinamic, and the reservoirs become infected in early ages through the contac with infected triatomines. Longitudinal studies, carried out in endemic areas of Argentina, have shown that dogs are the major donors of parasites to vectors and thus, principal contributors to transmission in these areas, and may serve as natural sentinels in the vigilance phase to detect introduction of T. cruzi in the domestic cycle.
More than 180 species or subspecies of small wild mammals have been found infected with T. cruzi in 20 countries of the American Continent. The most epidemiological important are reservoirs, such as some marsupials, edentates and rodents, because of their habits and favorable circumstantial local conditions, as disforesting, weeding and plowing, are capable to approximate to humans and play a significant role in linking the sylvatic and domestic cycles of the parasite. Three species and subspecies are the most relevant, a marsupial, the opossum (Didelphis sp.), an edentate, the armadillo (Dasypus sp.) and a rodent, the aguti (Dasyprota sp.). The opossum, widely distributed in the Western Hemisphere, is probably the most important wild reservoir because it is omnivorous and very prolific, with a great potential of adaptation and high T. cruzi infection indices, with no evidences of disease, been found in trees and shrubs close to dwellings and in attics and roofs.
In synthesis, the man, the dog and the opossum in their corresponding environments, are the most important known reservoirs of T. cruzi. Man has the highest epidemiological importance, because his considerable life expectancy of more than 60 years, his detectable T. cruzi parasitemias of over 40 years and his blood alone or mixed with blood of other vertebrates constitutes the feeding sources of 50.5 to 91.0% of domiciliary triatomines.