ESSENTIALS OF DIAGNOSIS
ESSENTIALS OF DIAGNOSIS
Inflammatory lesion at inoculation site.
Parasites in blood are diagnostic.
Heart failure, cardiac arrhythmias.
Serologic tests are usually diagnostic.
Chagas disease is caused by Trypanosoma cruzi, a protozoan parasite found only in the Americas; it infects wild animals and, to a lesser extent, humans from southern South America to the southern United States. An estimated 6–7 million people are infected, mostly in rural areas, with the highest national prevalence in Bolivia, Argentina, Paraguay, Ecuador, El Salvador, and Guatemala. Control efforts in endemic countries have decreased disease incidence to about 30,000 new infections and 12,000 deaths per year. The disease is often acquired in childhood. In many countries in South America, Chagas disease is the most important cause of heart disease. The vector is endemic in the southern United States where some animals are infected, and a few instances of local transmission have been reported.
T cruzi is transmitted by reduviid (triatomine) bugs infected by ingesting blood from animals or humans who have circulating trypanosomes. Multiplication occurs in the digestive tract of the bug and infective forms are eliminated in feces. Infection in humans occurs when the parasite penetrates the skin through the bite wound, mucous membranes, or the conjunctiva (eFigure 35–2). Transmission can also occur by blood transfusion, organ or bone marrow transplantation, congenital transfer, or ingestion of food contaminated with vector feces. From the bloodstream, T cruzi invades many cell types but has a predilection for myocardium, smooth muscle, and CNS glial cells. Multiplication causes cellular destruction, inflammation, and fibrosis, with progressive disease over decades.
Life cycle of Trypanosoma cruzi. An infected triatomine insect vector (or "kissing" bug) takes a blood meal and releases trypomastigotes in its feces near the site of the bite wound. Trypomastigotes enter the host through the wound or through intact mucous membranes, such as the conjunctiva
. Common triatomine vector species for trypanosomiasis belong to the genera Triatoma
, and Panstrongylus
. Inside the host, the trypomastigotes invade cells near the site of inoculation, where they differentiate into intracellular amastigotes
. The amastigotes multiply by binary fission
and differentiate into trypomastigotes, and then are released into the circulation as bloodstream trypomastigotes
. Trypomastigotes infect cells from a variety of tissues and transform into intracellular amastigotes in new infection sites. Clinical manifestations can result from this infective cycle. The bloodstream trypomastigotes do not replicate (different from the African trypanosomes). Replication resumes only when the parasites enter another cell or are ingested by another vector. The "kissing" bug becomes infected by feeding on human or animal blood that contains circulating parasites
. The ingested trypomastigotes transform into epimastigotes in the vector's midgut
. The parasites multiply and differentiate in the midgut
and differentiate into infective metacyclic trypomastigotes in ...