February 06, 2012
Think about everything that contributes to malaria transmission on a small-scale proximity to mosquitoes, the structure of a household, and myriad genetic and behavioral factors that influence the human-parasite interaction. All of these factors contribute to the heterogeneous transmission of malaria, meaning that mosquitoes don t bite everyone equally some households or areas are more affected than others.
A new paper in PLoS Medicine looks this heterogeneity, and the significance of malaria hotspots for malaria control and elimination strategies. As the authors point out, the current guidelines suggest focusing on this heterogeneity when a region nears elimination when there is low overall transmission, hotspots of higher prevalence can be identified and targeted as part of a latter stage effort to eradicate the disease.
But this new research, based on disease modeling, suggests that heterogeneity and hotspots exist in areas of high overall transmission too, even if they are harder to detect. And targeting these hotspots could more significantly reduce parasite prevalence.
What exactly is a hotspot? One example might be a small cluster of households (typically less than 1 km2) near a mosquito breeding site, but within a larger area of malaria transmission. A greater density of mosquitoes near the breeding site leads to particularly intensive malaria transmission in that cluster, forming a hotspot.
Targeting these hotspots, the authors argue, could be a more efficient way to reduce parasite prevalence, even within areas that are not yet in pre-elimination phases. Targeting also may allow for interventions that are considered too costly or complicated, or that wouldn’t be implemented across an entire population, like regularly applying larvicide to mosquito breeding sites.
More research is needed to understand how such targeting could work. For example, we need to know if hotspots are they stable over time, and how and if they fuel transmission to surrounding areas. Also, we need to determine how to find hotspots in high transmission areas, at sufficiently precise geographical levels to reach them effectively.
Still, if we can resolve these questions, targeting could be a strategic next step for high and low malaria transmission areas, a supplement to other approaches that cover populations but don t succeed in eliminating disease transmission.
From the paper s conclusion:
The recent successes of scaling up interventions for impact on malaria have revealed the policy gap of what to do afterwards when coverage is good yet malaria transmission continues. In this paper we have argued that the next evidence-based step is to tackle malaria hotspots. Although knowledge gaps exist, we argue that hotspot-targeted interventions should take place at all transmission levels where resources are sufficient and rapid reductions in malaria transmission will be seen.
Read it at PLoS Medicine.
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