The main purpose of this review is to bring together the scientific knowledge base (efficacies) and economic factors (costs, stakeholders) concerning aflatoxin risk-reduction strategies that could be deployed worldwide, and to highlight the importance of economic feasibility. Policy makers can use this information to decide: (1) whether the benefits (market and health) outweigh the costs of implementing the strategies, and (2) if so, then which stakeholders would pay the costs and which would benefit in the long run, to resolve potential mismatches in economic incentives (Wu et al. 2008
This information can also be useful to researchers who are developing further aflatoxin control strategies, in that they can roughly position their interventions among various existing strategies in terms of economic feasibility. It can also be useful to decision makers who want to weigh the relative importance of two categories of cost: the cost of preventing aflatoxin-related risks (to both markets and human health), and the cost of not preventing aflatoxin-related risks.
In preharvest settings, conventional breeding of maize and groundnuts to resist aflatoxin has shown great promise in terms of achievable efficacies. While initial research and development funding is of course necessary, once the resistant varieties are developed and disseminated, significant reduction of aflatoxin contamination can be achieved at very low, if any, additional cost to farmers. Replacement of local maize cultivars with agriculturally-improved varieties has been well-accepted by African farmers in recent history. It is estimated that a large part of 40% of present African maize yield is the result of planting improved cultivars (Smale and Jayne 2004
). Transgenic crops that demonstrate aflatoxin reduction, on the other hand, may encounter several problems regarding wide-scale adoption worldwide. One problem is cost. Though the actual cost per acre for transgenic seeds may not be high, farmers may be required to buy new seeds each season if the seeds were developed in the private sector. Such an expense for farmers who are used to saving seed from season to season might be considered unacceptable. Another problem is governmental regulations against commercialization and trade of transgenic organisms in many parts of the world. Hence, transgenic technologies in agriculture are at the moment best-suited to nations in which it is already customary to buy new seed each season, and where biosafety laws permit planting of transgenic seeds.
Biocontrol through atoxigenic strains of Aspergilli has shown significant promise in controlling aflatoxin in a variety of crops in both preharvest and postharvest settings. Depending on the product, costs vary widely; but low-cost options are available in LDCs that have naturally occurring atoxigenic strains in their native soils. Biocontrol can be extremely cost-effective in reducing aflatoxin-induced disease (Wu and Khlangwiset 2010
) because of the protection against aflatoxin contamination that lasts for at least 6 months postharvest. As with transgenic crops, there may be regulatory issues to overcome in different nations, associated with the application of fungal strains to agricultural fields.
Good agricultural practices – those that can reduce various stresses on crop plants and hence reduce fungal infection – can reduce aflatoxin contamination. Irrigation systems combined with insecticides can achieve extremely high efficacy in aflatoxin reduction, but capital costs to install the systems can be very high, as can operation and maintenance costs. These systems may not be affordable yet in many poorer LDCs.
In postharvest settings, physical methods to reduce aflatoxin accumulation are generally both less expensive and less risky than chemical methods. Physical sorting can remove the most contaminated food immediately postharvest. The postharvest intervention package described in Turner et al. (2005)
, which includes sorting as well as wooden drying pallets, natural-fiber storage bags, and insecticides, was estimated to be extremely cost-effective in reducing aflatoxin-induced HCC (Wu and Khlangwiset 2010
), without significant health or environmental risks. Chemical methods of destroying aflatoxin such as ammoniation and ozonation have extremely high efficacy levels at relatively low costs. However, handling ammonia can be dangerous if done improperly, and the process can cause reduced palatability and produce a byproduct which, though much less risky than AFB1
, may pose some health risks. Ozonation, because it appears to reduce protein efficiency in animals, may carry nutritional risks.
Dietary interventions to reduce aflatoxin risks can be considered forms of secondary prevention, as they do not actually reduce the amount of aflatoxin in the food, but can reduce its bioavailability in the body. NovaSil clay and chlorophyllin can both be produced at extremely low cost, and have shown significant reduction in biomarkers of aflatoxin-induced damage. Because both NS and chlorophyllin must be consumed at the same time as contaminated food in order to adsorb or sequester the aflatoxin, one potentially feasible mechanism is to blend these agents into a food item that is frequently used in local diets (e.g., maize meal). Green tea polyphenols would be an extremely cost-effective way to potentially reduce aflatoxin-induced health risks in cultures where green tea is already common in the diet. Otherwise, transportation costs and issues concerning the introduction of a relatively foreign drink (or pill) into the diet may render it impractical.
Chemoprevention through oltipraz and sulforaphane has shown some promise in reducing aflatoxin-induced HCC. Oltipraz is relatively expensive, however; and may not be practical as a long-term solution due to potential side-effects. With regard to obtaining sulforaphane from natural foods, at least two constraints exist: 1) the foods should ideally be locally produced, and 2) there is much variation in the concentration of the active compound in food. Therefore, it might be more reasonable to consider dietary chemoprevention as an additional intervention to other agricultural or clinical methods to reduce aflatoxin risks.
Hepatitis B vaccination has been employed in some degrees in Africa, initially with support from non–profit organizations such as the Global Alliance for Vaccines and Immunization (GAVI) and the Vaccine Fund (Zanetti et al. 2008
). However, if support is withdrawn, each country has to determine the feasibility and costs of continuing this program within its own budget. As much of the infrastructure and basic materials needed for vaccination have been established during the initial phase, and inexpensive and effective vaccines are available, HBV vaccine programs are overall a useful, cost-effective, and feasible strategy to reduce aflatoxin-induced HCC (and indeed, HCC in general). However, the vaccine has no effect in those already infected with HBV. Hence, other aflatoxin-reduction methods are desirable, particularly in nations where HBV prevalence is high and HBV vaccination is still scarce.
Overall, efficacy tends to be higher for agricultural interventions (preharvest and postharvest) and for HBV vaccination than for dietary interventions, to reduce aflatoxin-related health risks. However, there are times in which only dietary interventions would be helpful, such as in the case of an emergency. For example, if an acute aflatoxicosis outbreak is occurring, it is too late to adopt agricultural interventions or to administer HBV vaccines to reduce aflatoxin's health effects – at least, to counteract the current crisis. Adsorbent compounds in the diet would make the most sense in such an emergency, if it is suspected that available food sources still contain dangerously high aflatoxin levels, and if the food cannot be simply discarded (e.g., for reasons of scarcity).
A limitation with the cost estimates of several of these interventions is that many of the costs reflect estimates from pilot studies (field or clinical trials) or anecdotal data. Actual costs done on a large scale for some interventions cannot be estimated, because some of the interventions have never been implemented on a large scale. Because of economies of scale, this is more likely to result in cost overestimates in this study, rather than underestimates. This highlights the need for further research to more accurately establish costs and efficacy of aflatoxin-risk reduction interventions worldwide.
A critical component to implementing any or all of these methods is community education (Phillips et al. 2008
). Not only should educational efforts include how
to use the intervention properly to achieve maximum benefit regarding aflatoxin risk reduction, it should also include why
the interventions are important from health and market perspectives, so that users have incentive to continue with the interventions.
In summary, to reduce aflatoxin related problems in less developed countries, multiple types of interventions are potentially cost-effective; as they focus on different targets, offer different outcomes, and achieve those outcomes under different time constraints. Understanding the costs, efficacy, and affected stakeholders of different aflatoxin control interventions can help decision makers – be they government policymakers or farmers or consumers – to optimally allocate resources, with the ultimate aim of improving public health.