Epidemiology of Chagas disease in Mexico: an update.

With the continuing success of the Southern Cone Initiative against Chagas disease and steady progress of the Andean pact and Central American Initiatives, Mexico is among the last countries of Latin America to instigate a large-scale programme against Trypanosoma cruzi transmission. However, a national policy concerning Chagas disease control in Mexico has recently been developed. The Ministry of Health has approved a law about screening for anti-T. cruzi antibodies in the whole territory. Also, epidemiological surveillance and vector control programmes have started to inform regulation.

American trypanosomiasis (Chagas' disease) and blood banking in Mexico City: seroprevalence and its potential transfusional transmission risk.

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.

[Risk of transmission of Trypanosoma cruzi by blood transfusion in Mexico]. / Riesgo de transmisión de Trypanosoma cruzi por transfusión de sangre en México.

Data from the late eighties indicate that 1.6% of the Mexican population was infected with Chagas' disease and that transmission by way of blood transfusion was taking place in nearly every state, in areas of different sizes. The risk of transmission via that route has seldom been documented in Mexico, and for this reason a sentinel survey was conducted in 1994 in 18 blood banks belonging to the Ministry of Health and located in various states. The purpose of the study was to determine the risk of transmission via blood transfusion and to calculate the national prevalence of infection among potential donors, so as to have a set of general indicators of the prevailing disease burden and of the importance of this transmission route. Participants were selected on the basis of operating criteria: all government-run transfusion centers with the capacity to screen blood donors for at least one year and persons seeking to donate blood (n = 64,969) who satisfied the Official Mexican Standards (Norma Official Mexicana) for the therapeutic use of human blood and blood products. For the analysis of the results the centers were grouped according to migration flow in order to detect any possible influence the latter may have had on Chagas' disease transmission within the country. Screening was done with indirect hemagglutination using a reagent produced by the Instituto Nacional de Diagnóstico y Referencia Epidemiológicos and donated to the blood banks. Positive cases were confirmed by indirect immunofluorescence. Positive results were detected in 996 persons, for a prevalence of 1.5% (95% CI: 1.44 to 1.63). Concordance between the final results obtained by local labs and by the central lab was given by a kappa index of 0.87 (95% CI: 0.862 to 0.877). Cities having the highest emigration rates had three times the risk of transmission as compared to cities that drew immigrants (odds ratio = 2.82; 95% CI: 2.18 to 3.65). We recommend that mandatory serologic screening be enforced throughout Mexico, since migration makes it difficult to determine which areas are endemic.

Chagas disease. First congenital case report.

This is the first report of a congenitally transmitted case of Chagas disease occurring in Mexico, in a febrile premature newborn girl with low birth weight, hepatosplenomegaly and pneumonitis. Trypanosoma cruzi blood infection was detected using both direct smears and concentrated blood preparations. The patient's mother had a positive serological reaction by two techniques for anti-T. Cruzi antibodies. Two years after anti-chagastic treatment, the child has had a normal evolution, her serology is negative, and no abnormalities have been detected by electrocardiography.

[Serological diagnosis of Chagas disease: self-sufficiency and interlaboratory concordance]. / Diagnóstico serológico de la enfermedad de Chagas: autosuficiencia y concordancia interlaboratorios.

American trypanosomiasis (Chagas' disease) is becoming a relatively common condition in North America. Diagnosis at the chronic stage depends on demonstration of specific antibodies in body fluids, since parasitologic or pathologic diagnosis is uncertain at this stage. Therefore, standardization of immunodiagnostic techniques is mandatory, and it depends on antigen quality. Locally prepared antigens and crude extracts obtained from Mexican isolates, -both from infected vector and human cases-were compared using three different immunodiagnostic assays-indirect immunofluorescence, hemagglutination and enzyme linked immunosorbent assay (ELISA)-at two different laboratories from the Instituto Nacional de Cardiología and the Instituto Nacional de Diagnóstico y Referencia Epidemiológicos. Concordance between laboratories reached a significant Kappa value (0.8) and sensitivity, specificity and predictive values of individual diagnostic assays were adequate to use these tests in clinical diagnoses. This is the first attempt to standardize immunodiagnostic techniques in Mexico.

[Seroepidemiology of Chagas disease in Mexico]. / Seroepidemiología de la enfermedad de Chagas en México.

The lack of information about Chagas disease in Mexico, as well as the controversy concerning its importance, was the basis for the seroprevalence study of Trypanosoma cruzi in the National Seroepidemiology Survey (NSS). This information was representative of the national situation with regard to disease prevalences and other factors related to the nation's health. Unfortunately the NSS was not a very good information source for the study of trypanosomiasis americana, because its coverage in the disperse rural areas was poor. Nevertheless, the results of the NSS indicated that Chagas disease has an irregular distribution in Mexico with seroprevalences of 1.6, 0.5 and 0.2 for the different dilution levels used in the evaluation. The survey data showed Chagas disease to be less important than that mentioned by other authors. The NSS data confirmed the areas of disease transmission already reported and identified some new ones in Hidalgo, Chiapas and Veracruz. The survey also detected migratory workers with Chagas antibodies in Baja California border cities, a situation which indicates a risk for blood transfusion in areas of the country presumed to be free of the disease. Three quarters (74.5%) of the seropositive population were less than 39 years old. Moreover, the fact that children of less than four years were infected suggests that natural transmission is still very important in some areas. Although the seroprevalences were greater in the lower socio-economic groups, some persons of the higher socio-economic level were also affected. This situation may be explained by the fact that many of these persons own vacation homes in tropical areas.

A new method for diagnosis of Chagas' disease: diffusion-in-gel enzyme-linked immunosorbent assay.

The diffusion-in-gel enzyme-linked immunosorbent assay (DIG-ELISA) for antibodies to Trypanosoma cruzi was evaluated using formalinized epimastigotes as antigen. The results obtained by DIG-ELISA were compared with those obtained with the indirect hemagglutination test. The results of the DIG-ELISA showed that the reaction zone diameters obtained with sera from individuals with past or present exposure to T. cruzi were significantly greater than those obtained with normal human sera. All the sera from Chagasic individuals had a positive reaction in the test, whereas sera from normal individuals and individuals with toxoplasmosis or cutaneous leishmaniasis had a negative result. A close correlation was observed between the reaction zone diameters and antibody concentration (expressed as log2 of the serum dilution). Excellent correlation was observed between results obtained by the 2 serological tests. The data suggest that the DIG-ELISA is a promising serological test for measuring antibodies to T. cruzi.