Transmission
In Chagas-endemic areas, the main mode of transmission is through an insect vector called a triatomine bug. A triatomine becomes infected with T. cruzi by feeding on the blood of an infected person or animal. During the day, triatomines hide in crevices in the walls and roofs. The bugs emerge at night, when the inhabitants are sleeping. Because they tend to feed on people’s faces, triatomine bugs are also known as "kissing bugs". After they bite and ingest blood, they defecate on the person. Triatomines pass T. cruzi parasites (called trypomastigotes) in feces left near the site of the bite wound.
Scratching the site of the bite causes the trypomastigotes to enter the host through the wound, or through intact mucous membranes, such as the conjunctiva. Once inside the host, the trypomastigotes invade cells, where they differentiate into intracellular amastigotes. The amastigotes multiply by binary fission and differentiate into trypomastigotes, which are then released into the bloodstream. This cycle is repeated in each newly infected cell. Replication resumes only when the parasites enter another cell or are ingested by another vector. (See also: Life cycle and transmission of T. cruzi)
Dense vegetation (such as that of tropical rainforests) and urban habitats are not ideal for the establishment of the human transmission cycle. However, in regions where the sylvatic habitat and its fauna are thinned by economic exploitation and human habitation, such as in newly deforested areas, piassava palm culture areas, and some parts of the Amazon region, a human transmission cycle may develop as the insects search for new food sources.
T. cruzi can also be transmitted through blood transfusions. With the exception of blood derivatives (such as fractionated antibodies), all blood components are infective. The parasite remains viable at 4°C for at least 18 days or up to 250 days when kept at room temperature. It is unclear whether T. cruzi can be transmitted through frozen-thawed blood components.
Other modes of transmission include organ transplantation, through breast milk, and by accidental laboratory exposure. Chagas disease can also be spread congenitally (from a pregnant woman to her baby) through the placenta, and accounts for approximately 13% of stillborn deaths in parts of Brazil.
Oral transmission is an unusual route of infection, but has been described. In 1991, farm workers in the state of Paraíba, Brazil, were infected by eating contaminated food; transmission has also occurred via contaminated açaí palm fruit juice and sugar cane juice. A 2007 outbreak in 103 Venezuelan school children was attributed to contaminated guava juice.
Chagas disease is a growing problem in Europe, because the majority of cases with chronic infection are asymptomatic and because of migration from Latin America.
Read more about this topic: Chagas Disease