[Chagas disease: impact of Triatoma infestans control program in Alto del Carmen, Huasco Province, III Region Atacama, Chile].

A control program of Triatoma infestans has been carried out in Alto del Carmen, an endemic chagasic rural county in the III Region, Chile. The program started in 1988 with an attack phase consisting in a masshouse spraying with residual insecticide, followed by an entomological surveillance phase with health education for community participation and vector detection in eventually reinfested houses. A yearly evaluation in 1992, 1993, 1994 and 1995 was carried out in order to determine the effectiveness of vector control activities. In 1992, 24.1% of dwellings was infested, whereas in 1993, 1994 and 1995 the infestation rates were 3.9%, 2.8% and 4.0% respectively. The similar infestation rates found in 1993, 1994 and 1995 suggest passive dispersion of triatomas from areas without surveillance. Additionally, in 1994, 110 (16.0%) out of 688 examined people resulted serologically positive. It is noteworthy that all of the children in the 0-4 year age group--born after the attack phase--resulted serologically negative. This fact may indicate the interruption of vectorial transmission of Chagas' disease in Alto del Carmen county. It is concluded that the control activities performed in the county constitute good strategies to the Nacional Program of Control of T. infestans, but for the success of such a program it is necessary to integrate the efforts of all endemic areas with an active community participation.

González J ，Contreras MC ，Schenone H ，Adaos H ，Cabezas R ... -  《-》

[Control of the transmission of Trypanosoma cruzi in Argentina 1999].

Approximately 2 million people in Argentina are infected with Trypanosoma cruzi, the etiologic agent of Chagas disease, thereby constituting the major tropical disease in the country. As in other six Southern Cone countries, Triatoma infestans is the only or major vector of T. cruzi among human and domestic animals. In Argentina, a vertically structured National Chagas Control Program was established in 1962. Such a program pursued the elimination of domestic and peri-domestic populations of T. infestans through insecticidal spraying, and the serological control of blood donors to prevent transfusion-related infections. This program strongly reduced the nation-wide serological prevalence of T. cruzi in the population. For example, in 18 or 20 year-old men drafted into military service, the seroprevalence decreased from 10.1% in 1964 for those who had been born in 1944 to 1.9% in 1993 for those born in 1975. However, the vertical strategy failed to reach and sustain the surveillance phase in widespread rural areas with disperse populations due to its intrinsic limitations and the reduced priority level assigned to rural health programs. An alternative, horizontally-structured control strategy of T. infestans was developed and assayed in the Province of Santiago del Estero between 1985-1989, and 1991-1992. The projects demonstrated that insecticidal spraying carried out with community participation combined effectiveness and commitment in such a way as to produce a strong impact on house reinfestation and the extension of the area under entomological surveillance. This experience has been transferred in a chain of responsibilities to the personnel of the National Chagas Control Program, using participating workshops, procedural guidelines, and practical training. This personnel transferred the strategy using similar methods to the field health care agents and volunteers chosen by their own communities (community leaders). After the workshops, the leaders received all the materials needed to install and develop the ongoing surveillance activities: third generation pyrethroid insecticides, manuals, hand-operated sprayers, and sensor boxes to detect domiciliary infestations. From 1993 to 1998, a total of 15,000 health care agents or community leaders were trained. A total of 675,000 houses were sprayed with residual insecticides in the attack phase, and 850,000 houses entered the surveillance phase. This is the first time that such large coverage has been accomplished in Argentina. The network of laboratories installed a quality assurance program to current serological procedures applied to blood donors, organ transplant, and the detection and treatment of newborns to women sero-reactive for T. cruzi in Argentina. We expect to interrupt the vector-mediated transmission of T. cruzi in the next 18 months, but the sustainability of such a program depends on, at least, additional work with the community to achieve a change of attitudes and practices related to house infestation for the next 10 years. A social effort will be needed to cover those expenses, but the expected economic returns exceed largely the cost of any such program, as suggested by cost-benefit studies. To illustrate, the annual treatment costs of one Chagas patient can help maintain 25 households free from triatomine bugs in Argentina.

Segura EL ，Sosa Estani S ，Esquivel ML ，Gómez A ，Salomon OD ... -  《MEDICINA-BUENOS AIRES》

[Evaluation of vectors of Chagas' disease eradication programs in Chile by serological study of children under 10 years old].

Chagas' disease is a parasitic zoonosis with high prevalence in Chile. It is distributed in rural and periurban section in the northern most seven out of thirteen regions in which the country is divided, and affects about 142,000 individuals dispersed in most of the 165 counties sited in the chagasic zone. Triatoma infestans--intradomiciliary species--is the main and practically exclusive vector of Trypanosoma cruzi. Diverse tools may be utilized in order to interrupt the domestic cycle of transmission of T. cruzi: health education, housing improvement and elimination of vectors by dwelling insecticide sprayings. This last resource has received priority in Chile in the last 12 years. To evaluate the effectivity of the programs for eliminating T. infestans a serological study for Chagas' disease--comprising 8,767 children less than 10 years old from 27 rural counties insecticide sprayed in the last 12 years--was carried out. A global total of 125 (1.4%) children resulted positive, figure significantly lower than 5.4% found in 1982-1990 in the same age group. Distribution by regions of positive individuals showed a decrease of prevalence in each of them: III Region, from 9.8 to 1.0%, IV Region, 7.2 to 2.0%, V Region, 5.2 to 1.9%, and Metropolitan Region, 1.4% to 0.6. Even though positive children have still been found in 46.7% of localities of the studied counties, it is possible to affirm that the vector control programs have been effective and must be maintained, and increased in those localities with T. cruzi infection in children under 10 years of age, with the general aim of eradicate Chagas' disease transmission in Chile before 2000.

Lorca M ，Schenone H ，Contreras MC ，García A ，Rojas A ，Valdés J ... -  《-》

Chagas disease vector control through different intervention modalities in endemic localities of Paraguay.

In a field study carried out in three rural communities in Paraguay in a zone endemic for Chagas disease, we implemented three different vector control interventions--spraying, housing improvement, and a combination of spraying plus housing improvement--which effectively reduced the triatomine infestation. The reduction of triatomine infestation was 100% (47/47) in the combined intervention community, whereas in the community where housing improvement was carried out it was 96.4% (53/55). In the community where fumigation alone was used, the impact was 97.6% (40/41) in terms of domiciliary infestation. In all the houses where an intervention was made, an 18-month follow-up showed reinfestation rates of less than 10%. A serological survey of the population in the pre- and post-intervention periods revealed a shift in positive cases towards older age groups, but no significant differences were observed. The rate of seroconversion was 1.3% (three new cases) in the community with housing improvement only, but none of these cases could have resulted from vector transmission. The most cost-effective intervention was insecticide spraying, which during a 21-month follow-up period had a high impact on triatomine infestation and cost US$ 29 per house as opposed to US$ 700 per house for housing improvement.

Rojas de Arias A ，Ferro EA ，Ferreira ME ，Simancas LC ... -  《BULLETIN OF THE WORLD HEALTH ORGANIZATION》

[Epidemiology of Chagas' disease in Chile. Serological follow-up of 1,906 inhabitants from an endemic rural area, IV Region, 1991-1993].

The IV Region (29 degrees 30'-32 degrees 13' south lat.) is located in the center of the geographical area of distribution of Chagas' disease in Chile. Triatoma infestans is the main and almost exclusive vector of Trypanosoma cruzi in this country. The mean prevalence rate of T. cruzi human infection in urban and periurban sections of IV Region is 24.7%. To assess the impact of anti-T. infestans activities, by means of health education and sprayings of dwellings with insecticides, carried out in the IV Region since 1980, during January-February (summer) a serological follow-up to residents from 46 rural chagasic localities was performed. An indirect hemagglutination test and an indirect immunofluorescence test were done to each of the surveyed persons. In 1991, 303 (15.9%) out of 1,906 examined people resulted serologically positive. In 1992, previous discarding the positive individuals found in 1991, 1,334 persons were examined resulting positive 9 (0.7%). In 1993, 1,398 persons were surveyed and 26 (1.9%) were positive. It is noteworthy that none of these 35 positive persons had been surveyed in 1991, being difficult to assert if any was positive before. Two infants, daughters of positive mothers, serologically positive at the beginning, changed to negative in the following survey, indicating that it was a passive transfer of maternal specific antibodies. According to the results of this study, it is concluded that dwelling spraying with persistent-activity insecticides against T. infestans and health education are good tools in the control of T. cruzi human infection, particularly when the involved community participates.

Valdés J ，Contreras MC ，Mercado R ，Rojas A ，Correa V ，Schenone H ... -  《-》