Architecture and Vector Borne Disease Control

Frank Snowden, in his recent book on the eradication of malaria in Italy (Snowden 2006), described how Celli, in the early 1900s, was extremely successful in controlling malaria transmission simply by adding physical protection to houses. Only 1% of humans occupying such houses contracted disease in the middle of marshes riddled by mosquitoes, whereas hundreds of people in the control group without screens fell ill. Similarly, in the southern USA, screened porches played a significant role in eradicating malaria. Yet we seem to have forgotten about the potential of this method. The synergy here lies in the use of architecture as a discipline to help us design houses in such a manner that they minimize mosquito entry. Lindsay and colleagues (2002, 2003) showed recently how house entry can be controlled by simple changes in design or use of barriers, even without the use of insecticides. Thus, although we tend to think of houses in Africa as simple mud and thatch structures, more and more advanced house designs are seen, particularly in the urban but also in rural environments, where house design and disease control has a real potential, not only for malaria, but also for the control of tuberculosis, upper respiratory infections and diarrheal diseases. The recently coined concept of the "Casa segura", by Prof. Barry Beaty and colleagues, builds on the same principles of making entire houses and their future designs more suitable to control (vector-borne) diseases. With the major African malaria vectors preferring to feed indoors, there is ample scope to not protect at the individual level (e.g. through bed-net use) but at the household level (by making the entire house mosquito proof, or better still, by turning the entire house into a trap). Synergy can also be exploited by using architectural know-how to study airflows inside houses, and in particular how these can be manipulated. Value creation is the use of redirected airflow that contains human odours to a trap into which host-seeking female mosquitoes can be lured. Clearly, with African malaria vectors visiting a "point source" (i.e. the house), there will be many more things we can do to disrupt their contact with human hosts, besides using nets or indoor residual spraying. At present, we know nothing about the actual behavior of mosquitoes after they enter a house, apart from the fact that following blood feeding a considerable proportion remains indoors. Increased understanding of what drives the search for resting sites will enable more targeted application of insecticides (if these exert no excito-repellency) or other control methods. It is appreciated that such behaviors may differ for the various vectors and will depend on geographical and agro-ecological settings, which as a consequence necessitates detailed knowledge on mosquito behavior and ecology. This, in turn, hinders the development of "blanket technology" that can be applied from The Gambia to Djibouti, from Niger to South Africa (like nets or indoor residual spraying).

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