Browsing by Author "Opiyo, Mercy"

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Elevating larval source management as a key strategy for controlling malaria and other vector-borne diseases in Africa
(BMC, 2025-02-07) Okumu, Fredros; Moore, Sarah; Selvaraj, Prashanth; Yafin, Arnon; Juma, Elijah; Shirima, GloriaSalome; Majambere, Silas; Hardy, Andy; Knols, Bart; Msugupakulya, Betwel; Finda, Marceline; Kahamba, Najat; Thomsen, Edward; Ahmed, Ayman; Zohdy, Sarah; Chaki, Prosper; DeChant, Peter; Fornace, Kimberly; Govella, Nicodem; Gowelo, Steven; Hakizimana, Emmanuel; Hamainza, Busiku; Ijumba, Jasper; Jany, William; Kafy, Hmooda; Kaindoa, Emmanuel; Kariuki, Lenson; Kiware, Samson; Kweka, Eliningaya; Lobo, Neil; Marrenjo, Dulcisária; Matoke-Muhia, Damaris; Mbogo, Charles; McCann, Robert; Monroe,n April; Ndenga, Bryson; Ngowo, Halfan; Ochomo, Eric; Opiyo, Mercy; Reithinger, Richard; Sikaala, Chadwick; Tatarsky, Allison; Takudzwa, David; Trujillano, Fedra; Sherrard-Smith, Ellie
Larval source management (LSM) has a long history of advocacy and successes but is rarely adopted where funds are limited. The World Health Organization (WHO) guidelines on malaria prevention recommend the use of LSM as a supplementary intervention to the core vector control methods (insecticide-treated nets and indoor residual spraying), arguing that its feasibility in many settings can be limited by larval habitats being numerous, transient, and difficult to find or treat. Another key argument is that there is insufficient high-quality evidence for its effectiveness to support wide-scale implementation. However, the stagnation of progress towards malaria elimination demands that we consider additional options to the current emphasis on insecticidal commodities targeting adult mosquitoes inside homes. This letter is the result of a global, crossdisciplinary collaboration comprising: (a) detailed online expert discussions, (b) a narrative review of countries that have eliminated local malaria transmission, and (c) a mathematical modeling exercise using two different approaches. Together, these efforts culminated in seven key recommendations for elevating larval source management as a strategy for controlling malaria and other mosquito-borne diseases in Africa (Box 1). LSM encompasses the use of larvicide (a commodity) as well as various environmental sanitation measures. Together, these efforts lead to the long-term reduction of mosquito populations, which benefits the entire community by controlling both disease vector and nuisance mosquitoes. In this paper, we argue that the heavy reliance on large-scale cluster-randomized controlled trials (CRTs) to generate evidence on epidemiological endpoints restricts the recommendation of approaches to only those interventions that can be measured by functional units and deliver relatively uniform impact and, therefore, are more likely to receive financial support for conducting these trials. The explicit impacts of LSM may be better captured by using alternative evaluation approaches, especially high-quality operational data and a recognition of locally distinct outcomes and tailored strategies. LSM contributions are also evidenced by the widespread use of LSM strategies in nearly all countries that have successfully achieved malaria elimination. Two modelling approaches demonstrate that a multifaceted strategy, which incorporates LSM as a central intervention alongside other vector control methods, can effectively mitigate key biological threats such as insecticide resistance and outdoor biting, leading to substantial reductions in malaria cases in representative African settings. This argument is extended to show that the available evidence is sufficient to establish the link between LSM approaches and reduced disease transmission of mosquito-borne illnesses. What is needed now is a significant boost in the financial resources and public health administration structures necessary to train, employ and deploy local-level workforces tasked with suppressing mosquito populations in scientifically driven and ecologically sensitive ways. In conclusion, having WHO guidelines that recognize LSM as a key intervention to be delivered in multiple contextualized forms would open the door to increased flexibility for funding and aid countries in implementing the strategies that they deem appropriate. Financially supporting the scale-up of LSM with high-quality operations monitoring for vector control in combination with other core tools can facilitate better health. The global health community should reconsider how evidence and funding are used to support LSM initiatives.
Heterogeneous impacts for malaria control from larviciding across villages and considerations for monitoring and evaluation
(PLOS Pathogens, 2025-07-28) Smith, Ellie; Fillinger, Ulrike; Jean, Philippe; Winskill, Peter; Koudou, Benjamin; Tchicaya, Emile; Sanou, Antoine; Okumu, Fredros; Opiyo, Mercy; Majambere, Silas; Hamlet, Arran; Giovanni, Charles; Lambert, Ben; Churcher, Thomas
Malaria vector control tools currently focus on insecticide treated nets (ITNs) and indoor residual spraying in malaria-endemic locations, but additional preventative strategies are needed to address protection gaps. Larval source management (LSM) includes larvicide application to aquatic habitat and an array of alternative forms of environmental efforts. An individual-based transmission model for falciparum malaria is used to demonstrate the theoretical benefit of suppressing malaria adult mos- quito vector densities through LSM. The model simulates results of epidemiologicaltrials from Western Kenya (a hilly area with papyrus swamps adjacent to human settlements and moderate to high perennial malaria transmission) and Côte d’Ivoire (an area with Sudanese climate, reducing vegetation cover and high transmission) that applied larvicide alongside ITNs, and investigates whether estimated changes in adult density can be used to project changes in human malaria. In the Western Kenya setting generalised linear models estimate 82% (90% credible intervals: 64% – 92%) and 88% (79% – 94%) reductions in the proportion of adult Anopheles funestus and Anopheles gambiae complex mosquitoes respectively as measured by CDC light traps. In Côte d’Ivoire, an 82% (56% – 93%) reduction of the dominant An. gambiae vector was estimated using standard window trap and pyrethrum spray catch. Both studies had variable village-level impacts. The transmission dynamics model predicted that these entomological impacts would result in a reduction in malaria prevalence in children of 6-months to 10-years of age of 48 – 72% in Kenya, and a 11 – 78% reduction in all-age clinical incidence across villages in Côte d’Ivoire, which are broadly consistent with the empirically observed outcomes. High hetero- geneity between villages within the same study indicate that the relative or absolute reductions in mosquito adult density observed in these trials cannot be simply extrap-olated to other regions. The LSM strategy adopted, unit area covered, and multiple environmental covariates all contribute to differences in indicators that could be used to assess entomological impacts and the corresponding epidemiological outcomes. This important malaria control tool was impactful across all sites examined, though further work is needed to understand how best to use this tool in the fight against malaria.