CurrentMix) and the current mix without DDT policy (2035- NoDDT), both of which target malaria elimination by 2035. The figure also indicates the necessary additional malaria expenditures as percentage of GDP required to eliminate malaria by 2035 for the two scenarios (percentage values in brackets; 0.178% of GDP for 2035-CurrentMix and 0.199% for 2035-NoDDT). All expenditure figures assume a discount rate of 3%. The figure shows that malaria elimination by 2035 without the use of DDT entails higher total average yearly expenditures than the current mix scenario, which could be expected from the difference in insecticide costs. The estimated difference in costs between DDT and other IRS is based on the conservative assumption that the difference in production costs will remain unchanged, while it is likely that a large increase in the production of non-DDT IRS products will lead to a reduction in their cost. The average yearly costs for eliminating malaria by 2035 with the current combination of interventions and either a continued use of DDT for IRS or a rapid phase out of DDT for IRS can be compared with the yearly gains in GDP that result from malaria elimination. The continuation of DDT for IRS and a rapid phase out of DDT for IRS do not differ significantly in terms of the yearly gain in GDP that can be realized by the two policies. Both policies gradually approach the full yearly gains in GDP over time. Both policies stabilize on a percentage difference of approximately 1.6%, i.e., they appropriate most of the GDP loss due to malaria and thus realize 98.4% of the full potential yearly GDP gains. The remaining difference to the full potential GDP gains is due to the fact that these policies only gradually approach malaria elimina- tion. The hypothetical no malaria scenario, on the other hand, assumes no malaria as of 2012 and thus benefits from a more productive labor force as of 2012 as well as from the allocation of funds that would otherwise go to malaria prevention and treatment to economically more productive purposes such as investments in education and health. Indications of risks associated with the continued use of DDT. A contamination of agricultural products with DDT might imply losses in agricultural exports. Based on the data used in the production sector of the MMM, agricultural exports outside sub Saharan Africa have historically been around 0.1 percent of GDP. For our simulation runs into the future we therefore also assume agricultural exports outside SSA to be 0.1% of GDP. Figure S5 shows the average yearly value of 1%, 5% and 10% of the total agricultural exports (light grey bars) for the time period between 2017 and 2035, assuming a discount rate of 3%. This time period is equal to the time period for which the figure shows the average additional yearly costs of the 2035-NoDDT policy (as compared to the 2035-CurrentMix policy; dark grey bar). Figure S5 shows that the difference in costs of the continued use of DDT for IRS versus its rapid phase out lie between 1% and 5% of the value of agricultural exports outside SSA. This comparison can inform an assessment of the risk of losing agricultural exports because it provides an estimate of how the additional direct costs of rapidly phasing out DDT relate to the value of agricultural exports outside SSA. For each country in SSA this risk assessment is likely to be different as the importance of agricultural exports differs considerably. Indications of external effects of the continued use of DDT. In addition to the purely economic direct costs of phasing out DDT there are also possible external costs of DDT for human health and the environment. These costs are difficult to quantify because of the ecosystem-wide diffusion of DDT and the long-term nature of its manifold impacts. The most evident threat to human DDT versus Non-DDT Malaria Control health is the direct exposure of humans to DDT on dwellings’ walls. Based on our simulations, total DDT on dwellings is expected to grow up to nearly 90’000 tons in 2050 in our 2035- CurrentMix policy (dashed grey line in Figure S6). This value results from scaling up the current amount of DDT used for IRS and includes DDT concentrations that were accumulated on dwellings prior to 2010. On the contrary, in our 2035-NoDDT policy (solid grey line), DDT levels on dwellings are projected to decrease and reach levels very close to zero by 2020. Analyses of different intervention mixes and target years For putting the key question about the costs and benefits of a continued use of DDT for IRS versus its rapid phase out into perspective, we calculate the same costs and benefits for alternative combinations of IVM interventions. In this section we therefore calculate the malaria expenditures necessary to gradually scale up the current and alternative combinations of IVM interventions for achieving malaria elimination in 2025 or 2035. In addition to calculating the costs of elimination we compare these costs to the gain in GDP that could be achieved through malaria elimination. In order to eliminate malaria by 2025 with the current mix of interventions, the additional share of malaria expenditure on GDP needs to be 0.219% between 2017 and 2025. The total average yearly costs (malaria prevention expenditure) of this policy are 1.18 billion US dollars. Figure S7 summarizes the average yearly costs for all our policy-scenario combinations and arranges them in order of increasing costs. The figure also indicates the additional share of malaria expenditure on GDP for each policy-scenario combination in the brackets at the bottom of the bars. Figure S7a shows the average yearly costs for eliminating malaria by 2025 and Figure S7b the average yearly costs for the 2035 scenario. Figure S7 shows a clear order of intervention mixes in terms of their costs. Mixes focusing on the use of bed nets and on environmental management are cheaper than the currently applied mix, which, in terms of costs, is superior to a mix focusing on IRS. The mix focusing on IRS is the most expensive mix. This is mainly caused by the fact that IRS implies recurrent expenditure and does not have an important capital component. The bed net and EM mixes, on the other hand, require developing IVM infrastructure such as the production facilities for bed nets and, in case of EM, the construction of small-scale water or house screening infrastructure which, once developed, only have to be maintained and keep producing socio-economic benefits over their lifetime. When compared to Figure S4, Figure S7b shows that most of the tested combinations of IVM interventions have lower direct costs than the current combination, either with a continued use of DDT for IRS (2035-CurrentMix) or with a rapid phase out of DDT for IRS (2035-NoDDT in Figure S4). The average yearly costs of the different intervention mixes are also reflected in the necessary additional share of malaria expenditure on total GDP. The intervention mixes with 2025 as malaria elimination target year generally entail higher average yearly costs than the mixes for 2035. The 2025 interventions have to be more intensive to reach the shorter term goal than the 2035 interventions. Interestingly for the IRS focus, since the interven- tions are recurrent, average yearly expenditures are higher for elimination in 2035 than for elimination in 2025. Therefore, the later the elimination target is set to be reached, the higher the costs as the population base will have increased considerably in the additional malaria years. These costs can be compared to the yearly gains in GDP resulting from malaria elimination. If malaria is eliminated by 2025, all intervention mixes (all policies) gradually and similarly approach an appropriation of the potential yearly gains in GDP of PLoS ONE | www.plosone.org 7 November 2011 | Volume 6 | Issue 11 | e27771