How Infection Spreads
Most typically, this occurs when they are bitten by a triatomine insect, which is known in Latin America as a “kissing bug.” These insects feed on the blood of vertebrates and live in areas where blood supply is plentiful, such as in peoples’ homes. When they suck the blood of an animal that is infected with T. cruzi, they are able to pass the infection on to the next animal they feed upon.
Certain species of the kissing bug are well adapted to living with humans and it is thought that most cases of Chagas disease are spread from human to human by these insects.
Risk Factors
Acute-Phase Chagas Disease
The risk of developing the acute-phase disease is related, first, to whether a person lives in or visits an area where the T. cruzi parasite and the kissing bugs are endemic. Essentially, this area extends from the southern United States to northern Argentina and Chile.
Houses with adobe walls or thatched roofs seem to provide an especially attractive environment for kissing bugs. People living in such homes in endemic areas are particularly prone to develop Chagas disease.
However, measures to control the population of kissing bugs have been quite successful in some areas in Latin America.
Chronic-Phase Chagas Disease
In a person who has been infected with T. cruzi, several factors can increase the risk of developing chronic Chagas heart or gastrointestinal disease. These include:
Failure to seek medical help during the acute phase. If Chagas disease is recognized early on, treatment with antitrypanosomal drugs can eradicate the infection. Unfortunately, in the rural areas where Chagas disease now is most often found, most people with Chagas disease are never diagnosed during the acute phase. Genetic factors. It now appears that in people chronically infected with T. cruzi, genetic factors have a lot of influence on whether the disease will progress to cause heart or gastrointestinal disease. The integrity of the immune system. People with chronic Chagas disease are much more likely to develop heart disease or gastrointestinal problems if their immune systems are compromised, for instance, by other medical conditions such as HIV or by chemotherapy. Unknown factors. These known risk factors do not appear to answer all the questions. Researchers are actively working to identify why the immune system fails in the first place to get rid of the T. cruzi infection entirely, and why some people progress to severe chronic disease while others never do.
