Trial of a community-based intervention to decrease infestation of Aedes aegypti mosquitoes in cement washbasins in El Progreso, Honduras.

Washbasins and metal drums are important sources of Aedes aegypti mosquitoes in much of Latin America. When manual cleaning was found to be ineffective in eliminating mosquito larvae in a community-based control programme in El Progreso, Honduras, it was decided to develop and evaluate an improved method of removing mosquito eggs based on commonly-available materials. The method, named La Untadita ('The Little Dab', in English), consists of five steps: mixing chlorine bleach and detergent to make a paste, applying the mixture to the walls of the container, waiting 10 min, scrubbing with a brush, and finally rinsing with water. A field trial of the Untadita was conducted in 13 peri-urban neighbourhoods. At the first post-intervention survey, in spite of high levels of exposure to the community-based intervention, high levels of knowledge regarding the Untadita and high levels of its reported use, little or no impact was discernable on mosquito larvae and pupae. The method was then modified by increasing the recommended quantities of bleach and detergent and simplifying the instructions. In the second post-intervention survey, knowledge of the steps and their order increased further; the intervention neighbourhoods had significantly fewer algae on washbasin walls, an indicator of more effective cleaning; and numbers of pupae and 3rd and 4th instar larvae were significantly lower than in untreated neighbourhoods. Effective promotion of the Untadita should be able to control mosquito infestation in many washbasins, especially those in frequent use, thus reducing the need for chemical and biological larvicides that may be either more costly or less acceptable to householders.

Development of an indicator to evaluate the impact, on a community-based Aedes aegypti control intervention, of improved cleaning of water-storage containers by householders.

Householders in a community-based programme to control dengue in El Progreso, Honduras, are being encouraged to improve the cleaning of the water-storage containers in which many of the vectors thrive. The objective of the present study was to develop an indicator of the change occurring in human behaviour. Traditional Aedes aegypti larval indices do not differentiate between containers in which all the immature stages are present and those which hold only first- and second-instar larvae. However, it is not essential to prevent all larval development to limit transmission of pathogens by the adults; if the Ae. aegypti in the containers only manage to develop to young larvae before the containers are cleaned, then control of the vector in these containers will be effective. In field trials, sampling of third- and fourth-instar larvae in washbasins by taking five dips (quick immersions to a standard depth) with a hand-held net was found to be sufficient for estimating the true population size of that same cohort. This sampling method was then included in a large-scale survey of households, conducted for programme monitoring. An index was then developed as a summary measure of the degree of infestation of a washbasin by Ae. aegypti. This index was the sum of four variables assessed in the survey: presence of any immature stages (larvae and/or pupae); presence of pupae; detection of third-fourth-instar larvae in a five-dip sample; and a log-transformation of the number of larvae recovered. Based on this new index, the 884 washbasins encountered in the survey were classified as infestation-free (76.2%), or with low-(6.7%), medium-(14.9%) or high-level (2.2%) infestation. Application of the same procedure to 240 drums encountered in the survey showed that 66.3% were infestation-free and 9.2%, 17.1% and 7.4% had low-, medium- and high-level infestations, respectively. Compared with the traditional indices, this new index should be more sensitive to changes in human behaviour resulting from a control programme exposure than a simple, dichotomous variable (i.e. positive/negative for presence of immature stages). The use of such an index could make the control programme more efficient, allowing the greatest efforts to be targeted at households that have medium-high levels of infestation.

La Untadita: a procedure for maintaining washbasins and drums free of Aedes aegypti based on modification of existing practices.

Chlorine bleach and detergent are routinely used by householders in El Progreso, Honduras in the process of cleaning washbasins and drums, the two most important larval habitats of Aedes aegypti in the city. The efficacy of these materials in eliminating eggs, larvae, and pupae of Ae. aegypti was assessed under controlled conditions. The promising results obtained led to trials using a combination of chlorine bleach and detergent to apply to the walls of washbasins and drums as a method for eliminating eggs. The bleach maintained its ovicidal properties when mixed with detergent, and the detergent gave the mixture consistency so that it could be applied as a thin film to the walls. This new procedure was named the little dab (Untadita in Spanish) and allows households to direct their efforts against a stage of the mosquito life cycle that has been ignored in the past: the egg.

Vector control at the household level: an analysis of its impact on women.

The home is the setting where many vector-borne diseases are transmitted. Strategies for their control consequently have to involve the active participation of householders. In this paper we propose that low rates of participation in control activities frequently are related to the negative impact they have on women's power and authority within the domestic domain. This can arise from intrusion into domestic space by male vector control personnel, reorganization of the domestic environment as part of control activities, and promulgation of the idea that disease originates from within the home. In addition, women may need to make significant investments of both time and money in order to carry out the recommended control measures. Very little is known about the impact of vector control measures on women. This subject will assume increasing relevance as planners seek to involve householders, rather than the personnel of vertically-organized control programmes, in the implementation of vector control measures.

Effect of a community-based Aedes aegypti control programme on mosquito larval production sites in El Progreso, Honduras.

This paper describes the results of a trial to assess the efficacy in reducing the density of larval production sites of utilizing community involvement in the planning and implementation of an Aedes aegypti control programme, in a dengue-endemic city in Honduras. In addition to a substantial increase in knowledge about dengue transmission and prevention, a relative reduction in Ae. aegypti larval infestation indices was found in those city neighbourhoods where community involvement was utilized compared with their untreated counterparts. Several methods of improving the impact of this type of programme are discussed.

Physical and functional association of the T cell receptor and the T3 molecular complex on cytotoxic T cell clones that are differentially inhibitable by anti-T3 antibodies.

To examine the hypothesis that the antigen-specific T cell receptor (TcR) can function independently from the T3 complex on cytolytic T lymphocyte (CTL) clones, the physical and functional association of the T3 molecular complex and the T cell receptor has been examined on CTL clones that are differentially susceptible to inhibition by anti-T3 antibodies. From a panel of nine DPw2-specific CTL clones derived from the same donor, two clones (8.4 and 8.8) that were the most disparate in their susceptibility to inhibition by anti-T3 antibody were chosen for study. No significant differences were found between 8.4 and 8.8 for: the levels of cell surface expression of the T3 complex and the TcR; the ability to modulate T3 cell surface molecules; and the capacity of the TcR to comodulate with the T3 complex. Modulation of the T3 complex from clone 8.4 did not significantly affect cytolytic activity, and incubation of modulated 8.4 with additional anti-T3 antibody did not inhibit cytolytic activity. Although no T3 function for clone 8.4 could be demonstrated by simply blocking cytolytic activity with anti-T3 antibody, addition of limiting quantities of anti-T11 (but not anti-T4, anti-Tac, or anti-LFA-1) antibodies plus anti-T3 produced a marked synergistic inhibition of cytolysis. These results suggest that: CTL clones that are resistant to inhibition by anti-T3 antibodies actually have a physical and functional association between the T3 complex and the TcR; and the ability to demonstrate a functional role for T3 by antibody blocking may, in some cases, require limiting the involvement of the T11 molecule in CTL-target interactions. The most likely explanation for the observed heterogeneity in susceptibility to blocking by anti-T3 antibodies is, therefore, thought to be that individual CTL clones possess TcR with differential avidity for specific targets.