Large contractors in Africa: conundrums with malaria chemoprophylaxis

Despite high levels of naturally-acquired immunity (NAI) within local communities in malaria high transmission settings in Africa, such people often experience clinical disease during peak transmission months due to high parasite challenge. Major recruiters of unskilled labour in high-transmission malaria settings in Africa generally withhold chemoprophylactic medication from this large component of their labour force, which if administered during peak "malaria season" could reduce incidence of clinical malaria without unduly affecting NAI.

Naturally acquired immunity confers protection against severe clinical disease and death, but does not prevent mild clinical disease and, therefore, still results in worker absence and worker debilitation. Evidence exists that NAI persists despite periodic parasite clearance and therefore provides opportunity for drug prophylaxis during peak transmission months, which contributes to broader malaria elimination objectives, community well-being, and reduced absence from work. Such chemoprophylaxis could be by way of standard daily or weekly supervised administration of prophylactics during peak transmission months, or occasional intermittent preventive treatment (IPT), all aimed at reducing parasite burden and clinical disease. However, challenges exist regarding compliance with drug regimens over extended periods and high parasite resistance to recommended IPT drugs over much of Africa. Despite withholding chemoprophylactics, most large companies nevertheless pursue social responsibility programmes for malaria reduction by way of vigorous indoor residual spraying and bed net provision.

The lack of clear understanding regarding functioning of NAI and its role in malaria elimination campaigns, concerns about drug resistance and appropriate drug choice, lack of studies in the use of IPT in people other than pregnant women and small children, plus lack of guidance regarding drug options for IPT in the face of widespread resistance to sulfadoxine-pyrimethamine, means that large contractors in malaria endemic settings will likely continue to withhold malaria prophylactic drugs from locally-recruited workers, with adverse consequences on workforce well-being. Nevertheless, if the point of chemoprophylaxis is to reduce clinical malaria by way of reducing parasite challenge without significantly impacting NAI, then a comparable result can be achieved by implementation of effective vector reduction programmes which minimize parasite transmission but maintain NAI.