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Saving Lives, Buying Time: Economics of Malaria Drugs in an Age of Resistance
Repellants, Aerosols, and Fumigants
Many communities use aromatic smokes to deter mosquitoes. In The Gambia, tree bark combined with synthetic perfumes (locally known as churai) reduced the number of mosquitoes entering a room but not the incidence of malaria (Snow et al., 1987). In contrast, traditional fumigants in Sri Lanka decreased malaria (van der Hoek et al., 1998). In Thailand, a mixture of DEET (N,N-diethyl-m toluamide) and a paste made from a local tree (wood apple) was an effective repellant when applied to the skin (Lindsay et al., 1998).
Commercially manufactured coils containing pyrethroids or DDT also repel mosquitoes (Charlwood and Jolley, 1984; Bockarie et al., 1994). Although coils are cheap, households may spend substantial sums of money on items of this kind. In Dar es Salaam, Tanzania, average household expenditure on antimosquito measures was in the region of US$2-3 per month (Chavasse et al., 1999).
Environmental and Biologic Management
Since A. gambiae can breed in virtually any puddle, larval control in sub-Saharan Africa has always been challenging. Where vector breeding sites are few in number and easily identified, however, environmental or biologic control of larval breeding sites is often feasible. Petroleum oil larvicides have played an important part in mosquito control since the beginning of the 20th century. Breeding sites also may be eliminated by draining or filling in pools, modifying the boundaries of rivers or their run-off systems, and creating impoundments (reservoirs behind dams). Intermittent drying of rice fields, stream sluicing or flushing, salination of coastal marshes or lagoons (for example, using tidegates), shading of stream banks, and clearing of vegetation are naturalistic manipulations that proved beneficial in controlling certain vectors, primarily in India and southeast Asia. Although eclipsed by residual insecticides for several decades, many of these environmental methods of vector control are now back in vogue with strong WHO endorsement.
Biological control strategies, including use of bacteria such as Bacillus thuringiensis subsp. israelensis (Bti), or larvivorous fish, also have been combined with other control measures with variable success (Romi et al., 1993; Karch et al., 1993; WHO, 1999; Kaneko et al., 2000). Bti spores produce a toxin that is poisonous to mosquitoes and other aquatic insects but harmless to plants, animals, and humans. Bacillus sphaericus (Bsph) multiplies in polluted waters, and produces a longer-acting toxin than Bti; however, resistance to Bsph toxin is present in some mosquito populations in India, Brazil, and France (WHO, 1999).