Malaria: Prunes* to the rescue?

If you love someone, you give them flowers - Nigel Chaffey discovers there's also good reason to take away flowers too from the things you hate.
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It’s often claimed that malaria (a serious tropical disease spread by mosquitoes) has killed half the people who have ever lived. Regardless of whether that is true, at worst, malaria is certainly a notable killer of human beings, at best it can be extremely debilitating. Tackling malaria therefore is a global problem that deserves a global response. And just as in times of human conflict, one method of defeating an enemy is to disrupt or cut off his lines of supply, so too it seems in the case of the age-old battle against malaria.

Prosopis_juliflora
Prosopis juliflora. Image: Francisco Manuel Blanco / Wikipedia

A previously untried methodology, reported by Gunter Muller et al., involves reducing the food supply used by the mosquitoes (Anopheles spp.), females of which carry the malaria-causing Plasmodium parasite. Specifically, the flowering branches of Prosopis juliflora were removed from selected villages in Mali (West Africa). In such treated sites, there was a threefold drop in the older Anopheles females (which are most dangerous from a malarial-transmission point of view). This has been interpreted as a consequence of the much-reduced availability of a plant-derived sugar source; i.e. it has been suggested that the mosquitoes died of starvation.** Although this has yet to be established, any reduction in numbers of mosquitoes has to be a good thing from a human perspective. And such a ‘habitat-manipulation’ approach to malaria control has promise alongside other intervention methods to tackle this disease.

Given the importance of protecting humans from the scourge that is malaria – and the humanitarian desire to make such knowledge as widely available as possible – this important piece of work is appropriately published in an open-access journal. Prosopis now joins the growing list of plants – such as Cinchona (the source of quinine) and Artemisia (source of artemisinin) – that help humans in the fight against malaria.

One might here be tempted to say that if Prosopis hadn’t been introduced into Africa where it has established and thrives as an invasive alien (‘one of the world’s worst woody invasive plant taxa’), then maybe malaria wouldn’t be the serious issue that it is now. But one probably realises that the mosquitoes would use other plants as fuel and energy sources, and who wants to suggest that native species should all be de-flowered? Reducing mosquito fuelling sites in this way will also impoverish the local ecology – and who knows what knock-on effects/consequences there might then be to control of malaria-carrying mosquitoes? Pleasingly, and potentially life-savingly, this is a very direct demonstration of how gardening can improve one’s well-being!

* Define: prune

** This should not be interpreted as mosquitoes having gone vegetarian. Rather, it’s a recognition that they often need top-ups of energy from plant sources as they search for their next meal of human blood.

References

Muller, G. C., Junnila, A., Traore, M. M., Traore, S. F., Doumbia, S., Sissoko, F., … Beier, J. C. (2017). The invasive shrub Prosopis juliflora enhances the malaria parasite transmission capacity of Anopheles mosquitoes: a habitat manipulation experiment. Malaria Journal, 16(1). https://doi.org/10.1186/s12936-017-1878-9

Shackleton, R. T., Le Maitre, D. C., Pasiecznik, N. M., & Richardson, D. M. (2014). Prosopis: a global assessment of the biogeography, benefits, impacts and management of one of the world’s worst woody invasive plant taxa. AoB PLANTS, 6(0), plu027–plu027. https://doi.org/10.1093/aobpla/plu027

Gu, W., Müller, G., Schlein, Y., Novak, R. J., & Beier, J. C. (2011). Natural Plant Sugar Sources of Anopheles Mosquitoes Strongly Impact Malaria Transmission Potential. PLoS ONE, 6(1), e15996. https://doi.org/10.1371/journal.pone.0015996


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