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Seasonality affected malaria intervention efficacy
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Seasonal deployment of various malaria interventions could reduce spread and reproduction of the disease, according to recently published data.
An Imperial College London researcher used numerical methods to determine the seasonally varying basic reproduction number — the statistical measurement of secondary infections — of Plasmodium falciparum malaria in Africa. These data then were used to determine the effect size of disease interventions such as mass drug administration or indoor residual insecticide spraying, with the optimal timing of their use dictated by seasonal peaks in mosquito populations.
“For a given mathematical model of malaria transmission, the basic reproduction number can be calculated using formulae of varying complexity, as long as conditions are assumed to be constant over time,” the researcher wrote. “However mosquito numbers are highly seasonal in many places, in sub-Saharan Africa primarily due to rainfall. In a seasonal setting there are in general no known explicit formulae for basic reproduction numbers for vector-borne infections.”
The effect size of interventions with seasonal variation was shown to increase when deployed at optimal times. Mass drug administration had the greatest effect size when used in the low season, 3 months before the mosquito population’s peak. House spraying had a higher effect size when used before the start of high season, when mosquito population is at its most dense.
While these results were determined based on independent intervention receipt, the researcher wrote, combined effect sizes of interventions targeting different stages of the transmission cycle could be defined as the product of the separate events. However, the tendency for multiple programs to be received by the same population means a combined effect size would likely be less than that estimate.
“There has been a renewed focus in recent years on reducing malaria transmission, and even global eradication,” the investigator concluded. “In sub-Saharan Africa, the basic reproduction number due to P. falciparum malaria has been estimated at over 1,000 when there is intense transmission. So in order to eliminate the infection, it is necessary to combine multiple interventions and to use each one optimally.”
Disclosure: The researcher reports no relevant financial disclosures.
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