Amastigotes
infecting cells of muscle tissueMetacyclic epimastigotes of T. cruzi, secreted by the triatomine bug while taking a blood meal, are rubbed into the wound by the victim. Trypanosomes are taken up by macrophages and multiply intracellularly as amastigotes in the cytoplasm of the host cells. When these cells are loaded with amastigotes the latter transform to trypamastogotes and the host cells bursts open, releasing the trypamostigotes into the circulating blood, causing high parasiteamia and fever. These are the symptoms of the early stage of Chagas' disease. When antibodies against the trypomastigotes develop parasiteamia goes down and the trypomastigotes almost completely disappear from the blood to such a level that they cannot be detected other than by xenodiagnosis or by such sophisticated techniques as PCR (polymerase chain reaction).
Amastigotes
infecting cells of muscle tissue
Click here to see the different life-cycles stages of the tryapanosomatidae
However, trypanosomes remain present, hidden mainly as amastigotes inside cells of striated and smooth muscle and in nerve cells. This stage is called the chronic phase of the disease and it may last upto 20 - 30 years. The first period of this stage takes a symptomless course. However, the amasigotes express on the surface of their host cells some epitopes that resemble epitopes present on healthy cells as well and that are recognized by the cellular immune system of the host. This leads to an autoimmune reaction where healthy tissue is degraded leading to the typical symptoms of the late stage of hahgas' disease such as megacolon, megaoesophagus, weakening of the heart muscle and cardiac insufficiency and eventually heart failure.
X-rays of patients suffering from the late stage of Chagas' disease, one with megacolon and the other with a severe weakening and widening of the hart muscle.
A severe problem related to Chagas' disease is the presence of undetectable amounts of trypanosomes in the blood of asymptomatic carriers. If their blood is used for blood transfusion trypanosomes are transferred from an immune donor to a non-immune individual, which may lead to a fulminating parasitaemia and sudden death of the latter. For this purpose blood banks in South America have to treat all blood with gentian violet for 24 h at 4° C in order to kill any the trypomastigotes. An inconveniance related to this treatment is that the blood turns turns into purple and that some recipients may refuse infusion with blood treated this way.
