Question: I am working with rural African communities where we are struggling with contamination of farm products with residues from indoor residual spraying (ban on exports) – and are concerned about contamination of humans as well. Stepped up treatment of all persons diagnosed with malaria with AL. Like to assume that in dry season there are no malaria infected individuals in the community (it may be in visitors).
How do the mosquitoes get infected by the parasite so that they can infect humans? Do they get it from a (latently) malaria infected human? Is it an option to treat the whole community (200 persons) with Coartem at some time in the dry season to be malaria free? It is a relatively small investment to save the organic export business of the farmers.
Answer: All mosquitoes get infected through taking a blood meal from an infected human. The extent to which mosquitoes are able to pick up malaria from latently infected individuals (and therefore contribution of latent infection to overall transmission in a community or population) is still not well characterized but studies suggest they can, and therefore latent infection plays at least some role in maintaining transmission.
To my knowledge, treating communities during the dry season has not yet been tried as an option for ceasing transmission (largely, I suspect, since as you note visitors may still bring in new infections, reducing the efficacy of a blanket treatment approach). However, seasonal chemoprophylaxis, whereby at-risk individuals (usually children and pregnant women) take intermittent doses of anti-malaria medication (the WHO recommends sulfadoxine-pyrimethamine + amodiaquine in areas of Africa where the malaria is still susceptible to both medications; unfortunately SP resistance is on the rise) during the malaria season. WHO recommends it in areas with highly seasonal transmission, and it has proved quite successful in reducing overall malaria burden. Something like this might thus be worth exploring for the community in which you work.
I was not previously aware that indoor residual spraying could have an impact on exports from agricultural communities – I can see how it would be a serious concern. I can’t find any information from the WHO on this possible side effect, either – I imagine they would be very interested to learn about these unintended consequences of the intervention, as protecting livelihoods is of course also critically important when implementing public health measures.