In 2002, Jeffery Sachs estimated that the number of malaria cases would double by 2020 unless effective malaria control efforts were implemented (Sachs and Malaney, 2002). Since 2000, funding of malaria efforts, particularly in Africa, have increased dramatically. This has led to an estimated 17% reduction in the global incidence of malaria between 2000 and 2010. This drop is attributed to a scale-up of global malaria prevention efforts and funding (international aid totalled $2 billion USD in 2011). 2008-2011 saw delivery of enough insecticide treated bednets to prevent night time human-mosquito contact for approximately 600 million people. In 2010, indoor residual spraying of insecticides resulted in protection of 185 million people, representing 6% of the global population at risk (WHO 2011). While Sachs’ estimates may have been exaggerated, it is only through serious efforts that we have managed to curb disease growth—with a peak of 244 million cases in 2005 (WHO 2010)—and begin reducing the burden.
The use of insecticides for malaria control has seen a revival in recent years, through the technique of indoor residual spraying (IRS). IRS involves careful, controlled spraying of insecticides along the inside walls of a home or community building. This process greatly limits both human and wildlife exposure compared to the widespread field sprays and helicopter fly-over methods of the 1950s and 1960s (WHO 2006). In 2006 the World Health Organization encouraged a scale-up in IRS towards vector-borne disease control and concurrently endorsed DDT for this technique (Kolaczinski et al. 2007). Out of 108 malaria-burdened countries, 51 report the use of IRS. Thirteen of these countries use DDT (WHO 2011). There are 11 other chemicals recommended by WHO for use in IRS, including bendiocarb, malathion, lambda-cyhalothrin, and alphacypermethrin (WHO 2006).
Funding agencies, policy makers and program implementers have pushed public health researchers to quantify the benefits of IRS. Theoretically, the technology is capable of hugely decreasing the global malaria burden through killing mosquitoes and therefore stopping transmission. However, it is hard to generalize how effective IRS is at reducing malaria prevalence, as various researchers have shown conflicting results. Aspects of geography, entomology, human behavior, and community acceptance of the program could all contribute to why IRS is more successful in one community than in another. Few researchers have attempted to quantify the effects of IRS even on a small scale, and even fewer have addressed what factors might be major versus minor contributors to the relative success or failure of IRS programs around the world. Additionally, toxicity data from animal studies and recent epidemiological studies suggest that there may be long-term negative health consequences for those exposed to insecticides even at the low levels seen with IRS.
This creates an ethical dilemma. Are the benefits of using insecticides as a method for reducing malaria greater than the consequences of exposure to those insecticides?