[Control campaigns against Triatoma infestans in a rural community of northwestern Argentina].

Control campaigns against Triatoma infestans, the principal vector of Trypanosoma cruzi, have relied on the application of residual insecticides and have regarded the system as homogeneous. Reinfestation generally starts in peri-domestic residual foci or in preexisting foci that escaped spraying for diverse reasons. From these foci T. infestans adults actively invade other sites, or they are transported passively within objects or goods from infested communities. In the absence of additional spraying of insecticides after the attack phase, domiciliary reinfestation expanded exponentially to return to pre-spraying levels in 3-4 years in Amamá, Santiago del Estero. However, the rate of recovery of T. infestans abundance was much lower than that predicted by a simple mathematical model or in experimental field studies. Reinfestation did not progress homogeneously within the village. Two longitudinal studies in Santiago del Estero revealed that the presence of T. infestans-infested peri-domestic sites increased the risk of domiciliary reinfestation. "Key" sites where reinfestation started early were goat or sheep corrals, pig corrals, chicken houses, and store-rooms. Peri-domestic reinfestation is likely the result of multiple factors, such as insecticide breakdown by climatic agents, and the greater surface and availability of refuge and hosts in peri-domestic rather than domiciliary sites. Such environmental heterogeneity generates insecticidal effects heterogeneity and increases the probability of persistence of T. infestans even under control pressures. Several studies showed that sustained surveillance after the attack phase decreased sharply the domiciliary colonization by T. infestans and the percentage of bugs infected with T. cruzi, and the local incidence of infected children. The sustained elimination of T. infestans demands a scientific approach that is not only centered in insecticide use but that also includes the environment and house-holders in their specific social and political scenario.

Gürtler RE 《MEDICINA-BUENOS AIRES》

[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》

Factors limiting the domestic density of Triatoma infestans in north-west Argentina: a longitudinal study.

Reported are the environmental and demographic risk factors associated with the domestic infestation and density of Triatoma infestans in three heavily infested rural villages in Santiago del Estero Province, Argentina. In a one-factor unadjusted analysis, the number of T. infestans captured per person-hour was associated significantly and negatively with the use of domestic insecticides by householders, type of thatch used in the roofs and the age of the house; and positively with the following: degree of cracking of the indoor walls and presence of hens nesting indoors. In one model, using multiple linear regression and a backward stepwise elimination procedure, most of the variation in the overall abundance of T. infestans was explained by insecticide use and the presence of hens nesting indoors; in another model using the same procedure it was explained by insecticide use, bug density in 1988 and previous spraying with deltamethrin in 1985. Variations in bug density per capture stratum (household goods, beds, walls and roof) were explained by the bug density in other strata and by one or two of the following risk factors: hens nesting indoors, type of roof, presence of cracks in the walls and number of people living in the house. Bug density might be locally controlled by the availability of refuges in the roofs and walls, by the presence of hens nesting indoors and by the use of domestic insecticides. Certain local materials, such as a grass known as simbol, could be successfully used in rural housing improvement programmes aimed at reducing the availability of refuges for insects in the roof.

Cecere MC ，Gürtler RE ，Chuit R ，Cohen JE ... -  《BULLETIN OF THE WORLD HEALTH ORGANIZATION》

Spatio-temporal analysis of reinfestation by Triatoma infestans (Hemiptera: Reduviidae) following insecticide spraying in a rural community in northwestern Argentina.

The spatio-temporal reinfestation patterns by Triatoma infestans following a blanket insecticide spraying in the rural community of Amama in northwestern Argentina were analyzed using a geographic information system, satellite imagery, and spatial statistics. Domestic and peridomestic reinfestation by triatomine bugs was monitored from 1993 to 1997. Triatoma infestans was detected at least once in 75% of 2,110 sites evaluated. The prevalence of sites positive at least once for T. infestans during the study period increased sharply from 1993-1995 (0.6-2.9%) to November 1997 (32%). The initial source of T. infestans was a pig corral in southern Amama one year post-spraying. Subsequent infestations were clustered around this initial focus at a distance of approximately 400 meters starting in 1995. In 1996, clustering was maximized in sites within the same or in neighboring compounds at distances of 25-175 meters. An effective control program on the community level will be based on the spraying of actual epicenters and sites within 450 meters of these epicenters to prevent the propagation of T. infestans.

Cecere MC ，Vazquez-Prokopec GM ，Gürtler RE ，Kitron U ... -  《AMERICAN JOURNAL OF TROPICAL MEDICINE AND HYGIENE》

Effects of partial housing improvement and insecticide spraying on the reinfestation dynamics of Triatoma infestans in rural northwestern Argentina.

The long-term effects on domiciliary reinfestation by Triatoma infestans of smoothing the plaster of indoor walls prior to insecticide application (in Amamá village) relative to only insecticide application (in Trinidad-Mercedes villages) were evaluated in rural northwestern Argentina from 1992 to 1997. All domestic and peridomestic areas of each house were sprayed with 2.5% suspension concentrate deltamethrin at 25 mg/m(2) in October 1992, and infestations were assessed by various methods every 6 months. Domiciliary infestation decreased from 72-88% in 1992 to 6-17% in late 1995, to increase moderately thereafter without returning to baseline rates. Peridomestic sites were the first in becoming reinfested, and reached more abundant T. infestans populations than domiciliary areas. Domiciliary infestation rates and bug abundances were not significantly different between communities during surveillance. Domiciliary infestation rates in well-plastered houses were very low (5-9%) and approximately stable until 1996, but in houses with regular or bad plaster they consistently increased from 5 to 19-21% in both communities. Logistic multiple regression analysis showed that the likelihood of domestic infestation assessed through householders' collections was significantly and positively associated with the occurrence of an infested peridomestic site in the respective house, the occurrence of high-density domestic infestations before interventions, and well-plastered walls in 1996. Combining insecticide spraying and partial improvement of walls controlled domestic infestations and transmission of Trypanosoma cruzi effectively, but was not sufficient to eliminate T. infestans from the study area or increase the effectiveness of careful chemical control.

Cecere MC ，Gürtler RE ，Canale DM ，Chuit R ，Cohen JE ... -  《ACTA TROPICA》