Click T. cruzi is
most prevalent in Central and South America in areas where the insect vector Triatoma
infestans, or the reduviid bug, resides (See picture at left). This bug tends to
inhabit cool, dark, and damp areas which makes underdeveloped communites with dilapidated,
inadequate, or simply unsanitary housing especially at risk for the disease. The parasite
also resides in guinea pigs, a common South American pet which a cts as a resevoir for the
parasite in those communites. As an interesting side note, Chagas disease is also the
leading cause of cardiac faliure for men age 20-40 in Brazil due to population and
workforce movements into areas infested with the insect vector.
Blood Transfusions and Chagas' DiseaseAs transmission by the Reduuvid bug is beginning to be controlled through programs to eliminate vectors in endemic areas, blood transfusions have proved to be a significant route of transmission of Chagas' disease and, arguably, one of the hardest routes to control. The risk for contracting Chagas' disease through blood transfusions is more pronounced in urban settings because blood transfusions are more common in urban areas, and migrants from rural, more highly endemic areas come into cities and donate blood that is seropositive for T. cruzi. (Reiche 1996). In addition, any area that receives immigrants from endemic areas or any area that is endemic for Chagas' disease has a higher risk of transmission through blood transfusion. The problem of spread through blood transfusion is exacerbated by abuse of the practice of hemotherapy and by commercial use.
In recent times, the risk of contracting Chagas' disease from blood transfusions has
been confirmed by a study conducted in 10 countries of South and Central America in 1993
and in two countries of South America in 1994 (Schmunis 1998). This study found that the
risk for acquiring Chagas' disease through a blood transfusion is higher than the risk for
acquiring HIV, hepatitis B virus, hepatitis C virus, and Syphilis. The risk of
transmission of the disease if a person receives 500 mL of blood seropositive for T. cruzi
is between 12.5% and 25% (Zicker 1990). 
The rate of transmission through blood transfusions is decreasing. For example, in a study carried out in Londrina, Brazil, 1.4% of the blood samples studied from a blood bank between May 1990 and December 1994 were seropositive as compared to 7.0% rate of seropositivity that existed through the 1980's (Reiche 1996). In addition, in Quito, Ecuador, a study was carried out by the Red Cross that also indicated a "lower percentage positivity" from blood donors between July of 1994 and October of 1996 (Grijalva 1997). These decreases could be due to the delayed effects of vector control programs; increasing quality of blood transfusion services; increased awareness of the risks resulting in more rigorous prescreening of potential donors; and modifications in techniques used to detect T. cruzi (Reiche 1996 and Grijalva 1997).
In order to prevent further transmission through blood transfusion, several suggestions have been made in addition to continuing with the methods mentioned above. First, it is often suggested that more than one test should be used to test for seropositivity as often times, one test can give a positive and another can give a negative (Reiche 1996). In relation to this, a standard confirmatory test needs to be elucidated as no single test exists. Often blood banks use only the Enzyme-Linked Immunosorbent Assay (ELISA) which is cheap but not 100% effective (Grijalva 1997). Second, quality control at blood banks could be increased including refresher courses for personnel that cover methodology of the tests as well as stress the importance of the test (Grijalva 1997). Following the example of the Red Cross, donor selection questionnaires should include demographic and epidemiologic information relevant to Chagas' disease (Grijalva 1997). Finally, further research needs to be done on the chemical lepidine (a.k.a. WR6026 or Q45); it has been shown to eliminate trypomastigote forms of T. cruzi from blood without causing a lot of lysis of red blood cells (Chiari 1996).
Transplacental TransmissionAnother significant route of transmission of Chagas' disease is through vertical transmission, or transmission from a woman to her child. A study carried out in Santa Cruz, Bolivia between 1988 and 1989, for example, showed that 5% of all babies born to infected mothers in Santa Cruz presented with a congenital infection with T. cruzi, with babies weighing 2500 grams or less at the highest risk (Azogue 1993). At the time the study was carried out, there was a 54% incidence of seropositivity among pregnant women. In another study conducted in 1991 and 1992 in Paraguay, it was found that six months after birth, 10% of babies born to T. cruzi infected mothers were congenitally infected (Russomando 1998).
Newborns infected with T. cruzi can show prematurity, hepatomegaly, splenomegaly,
jaundice, anemia and alterations in the central nervous system (Russomando 1998). In
addition, an infection can cause infra-uterine growth retardation and deformations
(Bittencourt 1992). 
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While mothers can transmit the parasite when they are in either the acute or the chronic stage of disease, the risk is higher during the acute phase of the disease or when the mother presents an exacerbation of parasitemia (Bittencourt 1992). Transmission also occurs more frequently in younger mothers and older mothers with more than six kids (Azogue 1993). In addition, mothers with a previous history of fetal losses and previous offspring who have been infected carry a greater risk for congenitally infecting their children. Finally, women who live in an area of frequent congenital transmission are more likely to pass on the parasite to their children probably because it has been observed that different strains of T. cruzi have different tropisms for the placenta (Bittencourt 1992).
Trypomastigotes have been found in the milk of mothers during the acute phase of Chagas' disease, and there have been documented cases of transmission through breast-feeding (Bittencourt 1992). It was found, however, that the mother's nipples were bleeding at the time so the parasite could have been transmitted through the blood. It is recommended to infected mothers not to breast feed when their nipples are bleeding. The risk otherwise is not seen as great enough to tell all infected mothers not to breast feed.
It has been shown that the immunologic competence of the placenta may play an important role in the protecting the fetus from T. cruzi infection (Bittencourt 1992). It is necessary to conduct further research that may elucidate a way to enhance this protection during pregnancy. Many social factors also play into further roles for prevention. For example, a study showed that as the educational level of the mother increases, the rate of congenital transmission decreases because a more educated woman is better informed about family planning (Azogue 1993). Further work in terms of sociological studies need to be carried out to investigate what other social and cultural factors play into this mode of transmission and what can be done to prevent maternal child transmission.