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A serologic survey was carried out in four different geographic zones of Chiapas, Mexico. A total of 1,333 samples were collected from residents of thirteen communities located on the Coast, Central Mountain, Lacandon Forest and a zone called Mesochiapas. One hundred and fifty one seropositive individuals (11.3%) were identified. Human Trypanosoma cruzi infection was influenced by geography. In the Lacandon Forest and Central Mountains there was a higher seroprevalence 32.1 and 13.8% respectively, than on the coast (1.2%). In Mesochiapas there were no seropositive individuals among the 137 persons tested. An active transmission is probably continuing because seropositive cases (13.8%) were detected in children under 10 years of age. The vector recognized on the Coast was Triatoma dimidiata while in the Lacandon Forest it was Rhodnius prolixus.

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BACKGROUND: The anti-Trypanosoma cruzi antibodies isotype profile in Chagas' disease has been studied in relation to different clinical manifestations. A high titer of IgG anti-T. cruzi antibodies is found in patients with cardiac involvement, while a high titer of IgA anti-T. cruzi antibodies is associated with digestive forms. OBJECTIVE: The aim of this work was to analyze the IgG subclass reactivity of anti-T. cruzi antibodies in patients with chronic Chagasic cardiomyopathy. METHODS: Twelve consecutive chagasic patients were analyzed for IgG subclass reactivity to a T. cruzi antigenic extract. They had a complete clinical evaluation, peripheral EKG, echocardiography, left ventriculogram, and coronariography. RESULTS: All patients came from rural areas of Mexico and had lived in endemic zones for over seven years. They presented left ventricular endsystolic dimension above 42 mm in 58% (7/12) and ejection fraction below 50% in 58% (7/12). We found that IgG1 and IgG2 anti-T. cruzi antibodies showed higher titer than IgG3 antibodies, with consistently low titer of IgG4 antibodies. Expression of the four IgG subclasses of anti-T. cruzi antibodies suggest a mixed Th1/Th2-like immune response under a probably continuous chronic antigenic stimulation. On the other hand, high levels of IgG2 anti-T. cruzi antibodies showed a tendency to be associated with severe cardiomegaly. CONCLUSIONS: Our results suggest that a mixed Th1/Th2-like immune response may take place in chronic chagasic patients under a chronic antigenic stimulation.

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BACKGROUND: Although patients with chronic chagasic cardiopathy do have a strong immune response against Trypanosoma cruzi, they have transient and low parasitemia as well as tissue amastigote nests. When conventional studies were carried out, demonstration of such abnormalities is minimally achieved. Molecular biology may provide the best tools to demonstrate parasite persistence, which could be pathogenic in this progressive disease. METHODS: We studied 16 patients with chronic chagasic cardiopathy (CCC) at the Instituto Nacional de Cardiología Ignacio Chávez in Mexico City. Patients had undergone a complete clinical evaluation, and had antibodies against Trypanosoma cruzi. They came from different rural areas in Mexico. Blood samples were obtained and processed for hemoculture and PCR technique. A CCC necropsy case was also sought for the presence of parasite antigen or DNA, using immunohistochemistry and PCR methods in archival tissues. RESULTS: Five of 16 (31%) hemocultures demonstrated circulating T. cruzi; 60% occurred in persons between 25 and 40 years old. In contrast, we found a positive PCR amplification in 81%; therefore, molecular biology tools appear to be more sensitive for demonstrating parasite persistence. There were no correlations between parasitemic state and clinical findings or specific antibody titer. The autopsy case had parasite antigens and DNA in heart tissues. CONCLUSIONS: Chronic chagasic cardiopathy patients do have persistence of parasite even when parasitemia is low or absent. The continuous presence of a parasite load could maintain immune stimulus and perhaps enhance a pathogenic immune or autoimmune tissue damage in susceptible hosts.

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BACKGROUND: American trypanosomiasis (Chagas' disease), an anthropozoonosis fairly common in rural Latin America, has become an urban disease due to continuous migration, intra- and internationally. Blood transfusion, the second important pathway for transmission, increases its impact. Recognition of seropositive subjects among blood donors is now recommended, and clinical and serological screening enforced. Maneuvers to inactivate or remove Trypanosoma cruzi present in collected blood are recommended. METHODS: We surveyed voluntary donors at the National Institute of Cardiology in Mexico City in search of anti-T. cruzi by indirect immunofluorescence, ELISA, and Western blot analysis. Seropositive donors were identified and tested for immunoglobulin. We used types and fractions of donated blood to extract DNA and perform the PCR technique using kinetoplast primers seeking parasite DNA in blood. RESULTS: After 3,300 donors were screened, we identified 10 seropositive subjects (0.3%). These subjects were considered as indeterminate chagasic patients, came mainly from rural areas, and had IgG (100%) and IgA (30%) antibodies against a crude extract as well as a recombinant T. cruzi antigen. Identification of parasite DNA in red cell and platelet fraction was achieved from eight blood units. CONCLUSIONS: The present data provide evidence that blood donors at an urban hospital are seropositive for T. cruzi and at least 50% of donors carry the parasite potentially able to transmit T. cruzi in their cellular blood products. Serological screening should be included in routine blood-making. It is also necessary to adopt measures to inactivate or eliminate organisms in donated blood.

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