Geographic Distribution of T. cruzi
T. cruzi infection stretches from northern Mexico to southern Argentina, with an estimated 16 to 18 million infected individuals. There are more than 150 mammalian reservoirs. Human disease is the most prevalent in Brazil, where dogs and cats are important reservoirs.Chagas' disease has classically been considered a rural disease of Latin America; however, the trend of urbanization is changing the demographics and impact of the disease. 60% of the population in Latin America lives in urban areas. This urban migration has resulted in hundreds of thousands of infected individuals in Sao Paulo, Rio de Janeiro, Buenos Aires, and the United States. As more and more of the urban population is infected, this increases the risk of transfusional transmission, a factor that is especially dependent on the quality of the health care systems in these endemic countries.
There are two cycles of T. cruzi infection. The first is the sylvatic cycle which exists between wild vectors and hosts. The second, and newer, cycle is the domestic cycle between the vector and humans. This cycle is highly influenced by ecological and social factors and is dependent on human behavior. Evidence of this is the fact that Chagas' disease is not found in the native populations in the forests of central Brazil, although the sylvatic cycle exists. Due to the culture of these populations, the natural environment is preserved and the domestic cycle is not able to establish itself. Also, there have been only three cases diagnosed thus far in the United States, due to the inability of the vector to colonize human dwellings.
The Sylvatic and Urban (Domestic) Cycles
Many people live in rural areas in poorly constructed huts made of grass and mud, which the vector can colonize. Many individuals move to urban centers to survive due to the desperate living conditions in rural areas. This migration facilitates the spread of Chagas' disease to the cities.
The breeding ground for Reduviid bug
Control of T. cruzi can be accomplished from several different angles: social and political development; systematic elimination of the vector with insectide; housing improvement; and control of transfusional transmission. Although recent public health efforts such as the Southern Cone Initiative give hope to the control of the disease, ecological changes may have a negative impact on this effort. These changes include: human migration; agricultural projects; reforestation of areas with foreign species; and construction of dams. Expansion into previously "untouched" areas, such as the Amazon, opens of the possibility of expanding the domestic cycle of the disease. (http://www.dbbm.fiocruz.br/tropical/chagas/chapter4.html)