[Epidemiology of Chagas disease in Chile. Frequency of human Trypanosoma cruzi infection by age groups and regions]. / Epidemiología de la enfermedad de chagas en Chile. Frecuencia de infección humana por Trypanosoma cruzi por grupos de edad y por regiones.

Chagas' disease is endemic in rural-periurban sections of the northern half of Chile which includes the first seven political-administrative regions of the country (18 degrees 30'-34 degrees 36' South lat.). Data concerning to the results of an indirect hemagglutination test for Chagas' disease performed to 15,418 rural-periurban and 45,119 urban inhabitants fron the chagasic endemic regions are presented. Migrations from rural-periurban to urban areas have contributed to the dissemination of Trypanosoma cruzi infection. General rates of infection for rural-periurban (r-p) and urban (u) sections were 16.7% and 1.9% respectively. The higher prevalence rates were detected in Region III with 27.2% (r-p) and 3.9 (u) and Region IV with 24.7% (r-p) and 3.5% (u), while the lower prevalence rates corresponded to Region VI with 7.0% (r-p) and 0.8% (u). Serological positivity increased parallelly with age in all regions.

[Evaluation of a triatoma infestans eradication program in rural dwellings from the IV region, Chile, by means of serology for Chagas disease in 0-10 years old children]. / Evaluación de un programa de erradicación del Triatoma infestans en viviendas rurales de la IV región, Chile, mediante serología para la enfermedad de Chagas en niños de 0-10 años de edad.

The present study deals with the evaluation of the effectiveness of the measures employed in the control of Triatoma infestans, the vector of Trypanosoma cruzi infection (Chagas' disease), in the IV region of Chile through a serological follow up program. For this reason, a serological survey has been carried out in 2,783 children, from 0 to 10 years, who live in rural high endemic areas of the region. The sera were tested using an indirect hemagglutination test (IHAT) and ELISA techniques with results agreeing in 99.9% of the samples. In children with positive serology xenodiagnosis was performed and blood samples from the corresponding mothers were submitted to serology for Chagas' disease. These additional tests should allow to distinguish between congenital infection and vectorial transmission. It was observed that vectorial transmission of T. cruzi was interrupted in some localities where entomological control has been applied for 10 years, or lowered in those which have been submitted to desinsectations in the last 5 years. On the other hand, a relatively high prevalence of the infection has been detected in some localities. These results suggest an apparent increase of vectorial transmission, indicating the need of readjusting the dwellings insecticide sprayings activities to improve the measures against the vector.

[Diagnostic valve of ELISA-IgG for trichinosis using Melcher's antigen]. / Valor diagnóstico de la ELISA-IgG para triquinosis, usando antígeno de Melcher.

An enzyme-linked immunosorbent assay (ELISA) for trichinosis using a Melcher's antigen was developed for the detection of IgG antibodies in 41 serum samples from patients confirmed or suspected to have trichinosis by strong clinical and epidemiological evidences. ELISA- IgG was compared with a precipitin test (PT), a bentonite floculation test (BFT) and an indirect hemagglutination test (IHAT). The cut-off value was determined using serum samples from 67 apparently healthy persons employing two serum dilutions (1:100 and 1:500) with three standard deviations (SD). The sensitivity of ELISA- IgG was 97.6% and 95.2% using serum dilutions of 1:100 and 1:500 respectively, whereas the values for the other tests were: PT (92.7%), BFT (63.4%) and IHAT(85.4%). According to MacNemar test, ELISA-IgG did not present statistical significance (p > 0.05) compared with PT and IHAT, whereas all of them were different compared with BHT (p > 0.01). In order to find out the specificity of ELISA-IgG, additional 124 serum samples from individuals with other parasitoses, such as cysticercosis (31), fascioliasis (17), hydatidosis (51) and toxocariasis (25) were also tested. ELISA-IgG presented a specificity of 99.5% with both serum dilutions. The positive predictive values were 97.6 and 97.5%, whereas the negative one were 99.5 and 99.0% for 1:100 and 1:500 serum dilutions respectively. The use of ELISA-IgG and Melcher's antigen in the diagnosis of human trichinosis is discussed.