Browsing by Author "Yan, Guiyun"

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Anopheles larval ecology and physicochemical characterization of larval habitats in Dire Dawa: an area colonized by Anopheles stephensi in Eastern Ethiopia
(BioMed Central, 2026-08-01) Abiy, Ephrem; Degefa, Teshome; Balkew, Meshesha; Merga, Hailu; Zewdu, Deneke; Ayala, Alamayo; Atieli, Harrysone; Lee, Ming-Chieh; Zhou, Guofa; Yan, Guiyun; Yewhalaw, Delenasaw
Background: Understanding mosquito larval ecology is crucial for effective vector control strategies. While much is known about Anopheles larval habitat distribution, the impact of landscape (urban vs. rural) on Anopheles stephensi larval distribution and population dynamics in Ethiopia remains unclear. Methods: A longitudinal study was conducted from February 2023 to December 2024 in aquatic habitats in urban, peri-urban, and rural areas of Dire Dawa city administration, eastern Ethiopia. Mosquito larvae and pupae were collected and reared in a field insectary until adult emergence. The female Anopheles were morphologically identified and further confirmed via polymerase chain reaction (PCR). The physicochemical parameters of the larval habitats were measured via a HANNA multiparameter water probe. Statistical analyses included general linear models, ANOVA, logistic regression, paired sample t tests, chi-square tests, principal component analysis and correlation analyses to assess larval presence, density, and distribution in relation to water physicochemical parameters across the three ecological settings. Results: A total of 23,526 larvae and 1,808 pupae of Anopheles mosquitoes were collected from 856 man-made habitats (bricks, plastic sheets, steel drums, tire tracks, canal ditches, and barrels) and 53 natural habitats (river edges, animal hoof prints , ponds, and swamps) in urban, periurban, and rural areas. Uncovered cemented cisterns were the main human-made larval habitats; river edges were the main natural habitats. Anopheles larvae were absent in the steel drums and plastic barrels at the rural sites. Anopheles larval density significantly differed across the different ecological settings (F=7.8, df =1, 908, p=0.005) and among the different larval habitat types (F= 326.2, df = 1, 907, p< 0.001), land use/surrounding environment (χ2 = 32.6, df = 13, p = 0.002), vegetation (χ2 = 27.1, df =12, p=0.008), shade coverage (χ2 = 25.9, df = 15, p=0.039), substrate type (χ2 = 34.1, df = 6, p < 0.001), and competitor/predator presence (χ2 = 14.6, df = 1, p = 0.001). However, larval presence was not associated with the presence of larval interventions (χ2 = 1.3, df = 1, p = 0.250). Water pH (r = 0.26, n =102, p < 0.050) and water pressure (r = 0.21, n= 102, p < 0.050) were the only water physicochemical parameters that were positively correlated with An. stephensi presence. Conclusion: An. stephensi was dominant in urban areas but was also present in rural areas. Existing larval source management methods do not prevent Anopheles from occurring in many habitats, indicating an urgent need for improved strategies.
Hydrology-Based Evaluation of Irrigation and Cropping Practices in Relation to Malaria Transmission in Western Kenya
(2026-07-13) Jiang, Ai-Ling; Lee, Ming-Chieh; Atieli, Harrysone; Yan, Guiyun; Hsu, Kuo-lin
Irrigation is widely linked to increased malaria vector population and transmission in rural Africa, yet it remains essential for improving food security. Balancing agricultural productivity with public health therefore requires approaches that consider malaria risk. In this study, we integrated a hydrologic model with an agent-based malaria model to evaluate the impacts of cropping practices, irrigation strategies, and human and mosquito mobility on malaria transmission in Homa Bay, Kenya. We examined scenarios with single crops (either staple or cash crops) and mixed cropping systems, alongside irrigation methods including flood, intermittent, and drip irrigation. The modelling framework captures spatiotemporal dynamics of mosquito breeding habitats driven by crop water demands and irrigation scheduling. Results show that staple crops such as rice required approximately 12% more irrigation than vegetables but were associated with 3-7% lower transmission metrics. This suggests that the timing and spatial distribution of water application are more important than total irrigation volume in determining larval habitat conditions. Combining intermittent and drip irrigation reduced malaria prevalence by 44% relative to flood irrigation, as it limited the extent and persistence of larval habitats. Water-efficient irrigation strategies also concentrated transmission into smaller areas, making targeted interventions more feasible. Under these more heterogeneous risk patterns, human movement and vector dispersal played a critical role in shaping malaria prevalence. Overall, the integrated modelling approach provides a framework for evidence based agricultural planning that meets crop water demands while reducing malaria risk.
Reduced bio-efficacy of aged PermaNet® 3.0 Nets against local pyrethroid-resistant Anopheles arabiensis in Western Kenya
(Frontiers in Tropical Diseases, 2026-01-30) Machani, Maxwell G.; Zhou, Guofa; Oyweri, Job; Nzioki, Irene; Githure, John; Atieli, Harrysone; Wang, Chloe; Zhong, Daibin; Lee, Ming-Chieh; Afrane, Yaw A.; Yan, Guiyun
Background: Long-lasting insecticidal nets (LLINs) are central to malaria control and designed to protect for up to three years; however, increasing pyrethroid resistance undermines their effectiveness. Piperonyl butoxide (PBO) LLINs, designed to enhance pyrethroid efficacy, are recommended in high-resistance areas, yet their long-term operational bio-efficacy remains unclear. This study evaluated the killing efficacy of PBO LLINs over three years of field use compared to standard LLINs and monitored insecticide resistance in local Anopheles gambiae s.l. populations. Methods: During a trial in Muhoroni, western Kenya (2021–2024), standard and PBO LLINs were collected at 6, 18, and 36 months of use. Residual bio-efficacy was assessed using WHO cone bioassays against a susceptible Anopheles gambiae s.s. Kisumu strain and field An. gambiae s.l. populations. WHO tube and bottle assays determined insecticide resistance, while synergist assay assessed metabolic resistance. Quantitative polymerase chain reaction detected target-site mutations (kdr-1014 F/S and Ace-1 G119S). Results: Molecular identification confirmed all An. gambiae s.l. were Anopheles arabiensis, showing increasing pyrethroid resistance, with deltamethrin mortality declining from 96.3% (2021) to 22.7% (2024) while remaining susceptible to pirimiphos-methyl and clothianidin. PBO pre-exposure restored deltamethrin mortality from 22.7% to 98.9%. The frequency of 1014F increased from 0.09 to 0.17 and 1014S from 0.04 to 0.06, with no Ace-1 mutations detected. Standard LLINs retained >80% efficacy against the susceptible strain for 18 months but were below threshold against field mosquitoes even when new. PBO LLINs were effective at baseline against field populations but declined sharply, with mortality dropping to 24% by 6 months. Overall, both net types exhibited a marked decline in killing efficacy over time against field mosquitoes, with mortality falling < 20% within six months. Conclusion: Anopheles arabiensis showed increasing pyrethroid resistance, driven largely by metabolic mechanisms. Standard LLINs showed suboptimal killing efficacy against field populations, while PBO LLINs achieved high baseline efficacy but declined significantly by six months. These findings indicate that PBO LLINs can improve protection against resistant vectors but may be insufficient in high-resistance areas, underscoring the need for alternative non-pyrethroid interventions, strategic deployment, and revised LLIN re-distribution cycles aligned with their functional lifespan.