ORCID Profile
0000-0002-2462-6089
Current Organisation
University of California, Irvine
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Publisher: Public Library of Science (PLoS)
Date: 29-12-2020
DOI: 10.1371/JOURNAL.PONE.0244447
Abstract: Rapidly increasing pyrethroid insecticide resistance and changes in vector biting and resting behavior pose serious challenges in malaria control. Mosquito repellents, especially spatial repellents, have received much attention from industry. We attempted to simulate interactions between mosquitoes and repellents using a machine learning method, the Self-Propelled Particle (SPP) model, which we modified to include attractiveness/repellency effects. We simulated a random walk scenario and scenarios with insecticide susceptible/resistant mosquitoes against repellent alone and against repellent plus attractant (to mimic a human host). Simulation results indicated that without attractant/repellent, mosquitoes would fly anywhere in the cage at random. With attractant, all mosquitoes were attracted to the source of the odor by the end. With repellent, all insecticide-susceptible mosquitoes eventually moved to the corner of the cage farthest from the repellent release point, whereas, a high proportion of highly resistant mosquitoes might reach the attractant release point (the human) earlier in the simulation. At fixed concentration, a high proportion of mosquitoes could be able to reach the host when the relative repellency efficacy (compare to attractant efficacy) was , whereas, no mosquitoes reached the host when the relative repellency efficacy was 1. This result implies that repellent may not be sufficient against highly physiologically insecticide resistant mosquitoes, since very high concentrations of repellent are neither practically feasible nor cost-effective.
Publisher: Springer Science and Business Media LLC
Date: 13-03-2018
Publisher: Springer Science and Business Media LLC
Date: 27-01-2020
DOI: 10.1186/S40249-019-0620-Y
Abstract: Irrigated agriculture is key to increase agricultural productivity and ensure food security in Africa. However, unintended negative public health impacts (e.g. malaria) of such environmental modification have been a challenge. This study assessed the ersity and distribution of breeding habitats of malaria vector mosquitoes around Arjo-Dedessa irrigation development site in Southwest Ethiopia. Anopheline mosquito larvae were surveyed from two agroecosystems, ‘irrigated’ and ‘non-irrigated’ areas during the dry (December 2017–February 2018) and wet (June 2018–August 2018) seasons. Mosquito habitat ersity and larval abundance were compared between the irrigated and non-irrigated areas. The association between anopheline mosquito larvae occurrence and environmental parameters was analysed using Pearson chi-square. Multiple logistic regression analysis was used to determine primary parameters that influence the occurrence of anopheline larvae. Overall, 319 aquatic habitats were surveyed during the study period. Around 60% ( n = 152) of the habitats were positive for anopheline mosquito larvae, of which 63.8% ( n = 97) and 36.2% ( n = 55) were from irrigated and non-irrigated areas, respectively. The number of anopheline positive habitats was two-fold higher in irrigated than non-irrigated areas. Anopheline larval abundance in the irrigated area was 16.6% higher than the non-irrigated area. Pearson’s chi-square analysis showed that season ( χ 2 = 63.122, df = 1, P 0.001), agroecosystem (being irrigated or non-irrigated) ( χ 2 = 6.448, df = 1, P = 0.011), and turbidity ( χ 2 = 7.296, df = 2, P = 0.025) had a significant association with larval anopheline occurrence. The study showed a higher anopheline mosquito breeding habitat ersity, larval occurrence and abundance in the irrigated than non-irrigated areas in both dry and wet seasons. This indicates that irrigation development activities contribute to proliferation of suitable mosquito breeding habitats that could increase the risk of malaria transmission. Incorporating larval source management into routine malaria vector control strategies could help reduce mosquito population density and malaria transmission around irrigation schemes.
Publisher: Springer Science and Business Media LLC
Date: 26-10-2018
Publisher: Public Library of Science (PLoS)
Date: 14-01-2022
DOI: 10.1371/JOURNAL.PONE.0261713
Abstract: Indoor residual spraying and insecticide-treated nets are among the key malaria control intervention tools. However, their efficacy is declining due to the development and spread of insecticide resistant vectors. In Ethiopia, several studies reported resistance of An . arabiensis to multiple insecticide classes. However, such data is scarce in irrigated areas of the country where insecticides, pesticides and herbicides are intensively used. Susceptibility of An . gambiae s.l. to existing and new insecticides and resistance mechanisms were assessed in Arjo-Didessa sugarcane plantation area, southwestern Ethiopia. Adult An . gambiae s.l. reared from larval upal collections of Arjo-Didessa sugarcane irrigation area and its surrounding were tested for their susceptibility to selected insecticides. Randomly selected An . gambiae s.l. (dead and survived) s les were identified to species using species-specific polymerase chain reaction (PCR) and were further analyzed for the presence of knockdown resistance ( kdr ) alleles using allele-specific PCR. Among the 214 An . gambiae s.l. s les analyzed by PCR, 89% (n = 190) were An . amharicus and 9% (n = 20) were An . arabiensis . Mortality rates of the An . gambiae s . l . exposed to deltamethrin and alphacypermethrin were 85% and 86.8%, respectively. On the other hand, mortalities against pirmiphos-methyl, bendiocarb, propoxur and clothianidin were 100%, 99%, 100% and 100%, respectively. Of those sub-s les ( An . amharicus and An . arabiensis ) examined for presence of kdr gene, none of them were found to carry the L1014F (West African) allelic mutation. Anopheles amharicus and An . arabiensis from Arjo-Didessa sugarcane irrigation area were resistant to pyrethroids which might be synergized by extensive use of agricultural chemicals. Occurrence of pyrethroid resistant malaria vectors could challenge the ongoing malaria control and elimination program in the area unless resistance management strategies are implemented. Given the resistance of An . amharicus to pyrethroids, its behavior and vectorial capacity should be further investigated.
Publisher: Springer Science and Business Media LLC
Date: 09-01-2021
DOI: 10.1186/S12879-020-05761-6
Abstract: Transmission stemming from asymptomatic infections is increasingly being recognized as a threat to malaria elimination. In many regions, malaria transmission is seasonal. It is not well understood whether Plasmodium falciparum modulates its investment in transmission to coincide with seasonal vector abundance. We s led 1116 asymptomatic in iduals in the wet season, when vectors are abundant, and 1743 in the dry season, in two sites in western Kenya, representing different transmission intensities (Chulaimbo, moderate transmission, and Homa Bay, low transmission). Blood s les were screened for P. falciparum by qPCR, and gametocytes by pfs25 RT-qPCR. Parasite prevalence by qPCR was 27.1% (Chulaimbo, dry), 48.2% (Chulaimbo, wet), 9.4% (Homabay, dry), and 7.8% (Homabay, wet). Mean parasite densities did not differ between seasons ( P = 0.562). pfs25 transcripts were detected in 119/456 (26.1%) of infections. In the wet season, fewer infections harbored detectable gametocytes (22.3% vs. 33.8%, P = 0.009), but densities were 3-fold higher (wet: 3.46 transcripts/uL, dry: 1.05 transcripts/uL, P 0.001). In the dry season, 4.0% of infections carried gametocytes at moderate-to-high densities likely infective ( 1 gametocyte per 2 uL blood), compared to 7.9% in the wet season. Children aged 5–15 years harbored 76.7% of infections with gametocytes at moderate-to-high densities. Parasites increase their investment in transmission in the wet season, reflected by higher gametocyte densities. Despite increased gametocyte densities, parasite density remained similar across seasons and were often below the limit of detection of microscopy or rapid diagnostic test, thus a large proportion of infective infections would escape population screening in the wet season. Seasonal changes of gametocytemia in asymptomatic infections need to be considered when designing malaria control measures.
Publisher: Cold Spring Harbor Laboratory
Date: 20-03-2020
DOI: 10.1101/2020.03.20.000281
Abstract: Rapidly increasing pyrethroid insecticide resistance and changes in vector biting and resting behavior pose serious challenges in malaria control. Mosquito repellents, especially spatial repellents, have received much attention from industry. Many of these repellents contain the same or similar chemicals as those used in insecticides. Does resistance to insecticides affect the efficacy of spatial repellents? We attempted to simulate interactions between mosquitoes and repellents using a machine learning method, the self-propelled particle (SPP) model, which we modified to include attractiveness/repellency effects. We simulated a random walk scenario and scenarios with insecticide susceptible/resistant mosquitoes against repellent alone and against repellent plus attractant (to mimic a human host). We assumed attractant odors and repellent chemicals diffused randomly and omnidirectionally, and that mosquitoes were confined in a cubic cage. We modified the velocity and direction components of SPP using attraction/repulsion rates and concentrations. Simulation results indicated that without attractant/repellent, mosquitoes would fly anywhere in the cage at random. With attractant, mosquitoes might or might not fly toward the source (i.e., the human), depending on the simulation time (and thus the attractant concentration distribution). Eventually, however, all mosquitoes were attracted to the source of the odor. With repellent, results depended on the amount of chemical used and the level of mosquito insecticide resistance. All insecticide-susceptible mosquitoes eventually moved to the corner of the cage farthest from the repellent release point. Surprisingly, a high proportion of highly resistant mosquitoes might reach the attractant release point (the human) earlier in the simulation when repellent was present compare to no repellent was present. At fixed concentration, a high proportion of mosquitoes could be able to reach the host when the relative repellency efficacy (compare to attractant efficacy) was , whereas, no mosquitoes reached the host when the relative repellency efficacy was 1. This result implies that repellent may not be sufficient against highly physiologically insecticide resistant mosquitoes, since very high concentrations of repellent are neither practically feasible nor cost-effective.
Publisher: Springer Science and Business Media LLC
Date: 22-09-2020
DOI: 10.1186/S12936-020-03416-0
Abstract: Despite extensive irrigation development in Ethiopia, limited studies assessed the impact of irrigation on malaria vector mosquito composition, abundance and seasonality. This study aimed to evaluate the impact of sugarcane irrigation on species composition, abundance and seasonality of malaria vectors. Adult Anopheles mosquitoes were collected using CDC light traps from three irrigated and three non-irrigated clusters in and around Arjo-Didessa sugarcane irrigation scheme in southwestern Ethiopia. Mosquitoes were surveyed in four seasons: two wet and two dry, in 2018 and 2019. Mosquito species composition, abundance and seasonality were compared between irrigated and non-irrigated clusters. Anopheles mosquitoes were sorted out to species using morphological keys and molecular techniques. Chi square was used to test the relationships between Anopheles species occurrence, and environmental and seasonal parameters. Overall, 2108 female Anopheles mosquitoes comprising of six species were collected. Of these, 92.7% (n = 1954) were from irrigated clusters and 7.3% (n = 154) from the non-irrigated. The Anopheles gambiae complex was the most abundant (67.3%) followed by Anopheles coustani complex (25.3%) and Anopheles pharoensis (5.7%). PCR-based identification revealed that 74.7% (n = 168) of the An. gambiae complex were Anopheles arabiensis and 22.7% (n = 51) Anopheles amharicus . The density of An. gambiae complex (both indoor and outdoor) was higher in irrigated than non-irrigated clusters. The overall anopheline mosquito abundance during the wet seasons (87.2% n = 1837) was higher than the dry seasons (12.8% n = 271). The ongoing sugarcane irrigation activities in Arjo-Didessa created conditions suitable for malaria transmitting Anopheles species ersity and abundance. This could drive malaria transmission in Arjo-Didessa and its environs in both dry and wet seasons. Currently practiced malaria vector interventions need to be strengthened by including larval source management to reduce vector abundance in the irrigated areas.
Publisher: Springer Science and Business Media LLC
Date: 12-05-2021
DOI: 10.1038/S41598-021-89576-8
Abstract: Larval source management has gained renewed interest as a malaria control strategy in Africa but the widespread and transient nature of larval breeding sites poses a challenge to its implementation. To address this problem, we propose combining an integrated high resolution (50 m) distributed hydrological model and remotely sensed data to simulate potential malaria vector aquatic habitats. The novelty of our approach lies in its consideration of irrigation practices and its ability to resolve complex ponding processes that contribute to potential larval habitats. The simulation was performed for the year of 2018 using ParFlow-Common Land Model (CLM) in a sugarcane plantation in the Oromia region, Ethiopia to examine the effects of rainfall and irrigation. The model was calibrated using field observations of larval habitats to successfully predict ponding at all surveyed locations from the validation dataset. Results show that without irrigation, at least half of the area inside the farms had a 40% probability of potential larval habitat occurrence. With irrigation, the probability increased to 56%. Irrigation d ened the seasonality of the potential larval habitats such that the peak larval habitat occurrence window during the rainy season was extended into the dry season. Furthermore, the stability of the habitats was prolonged, with a significant shift from semi-permanent to permanent habitats. Our study provides a hydrological perspective on the impact of environmental modification on malaria vector ecology, which can potentially inform malaria control strategies through better water management.
Publisher: American Society of Tropical Medicine and Hygiene
Date: 11-10-2022
Abstract: Food insecurity, recurrent famine, and poverty threaten the health of millions of African residents. Construction of dams and rural irrigation schemes is key to solving these problems. The sub-Saharan Africa International Center of Excellence for Malaria Research addresses major knowledge gaps and challenges in Plasmodium falciparum and Plasmodium vivax malaria control and elimination in malaria-endemic areas of Kenya and Ethiopia where major investments in water resource development are taking place. This article highlights progress of the International Center of Excellence for Malaria Research in malaria vector ecology and behavior, epidemiology, and pathogenesis since its inception in 2017. Studies conducted in four field sites in Kenya and Ethiopia show that dams and irrigation increased the abundance, stability, and productivity of larval habitats, resulting in increased malaria transmission and a greater disease burden. These field studies, together with hydrological and malaria transmission modeling, enhance the ability to predict the impact of water resource development projects on vector larval ecology and malaria risks, thereby facilitating the development of optimal water and environmental management practices in the context of malaria control efforts. Intersectoral collaborations and community engagement are crucial to develop and implement cost-effective malaria control strategies that meet food security needs while controlling malaria burden in local communities.
Publisher: Oxford University Press (OUP)
Date: 17-08-2020
Abstract: To improve food security, investments in irrigated agriculture are anticipated to increase throughout Africa. However, the extent to which environmental changes from water resource development will impact malaria epidemiology remains unclear. This study was designed to compare the sensitivity of molecular markers used in deep licon sequencing for evaluating malaria transmission intensities and to assess malaria transmission intensity at various proximities to an irrigation scheme. Compared to ama1, csp, and msp1 licons, cpmp required the smallest s le size to detect differences in infection complexity between transmission risk zones. Transmission intensity was highest within 5 km of the irrigation scheme by polymerase chain reaction positivity rate, infection complexity, and linkage disequilibrium. The irrigated area provided a source of parasite infections for the surrounding 2- to 10-km area. This study highlights the suitability of the cpmp licon as a measure for transmission intensities and the impact of irrigation on microgeographic epidemiology of malaria parasites.
Publisher: American Society of Tropical Medicine and Hygiene
Date: 03-05-2023
Abstract: As malaria control and elimination efforts r up in Ethiopia, more sensitive tools for assessing exposure to coendemic Plasmodium falciparum and Plasmodium vivax are needed to accurately characterize malaria risk and epidemiology. Serological markers have been increasingly explored as cost-effective tools for measuring transmission intensity and evaluating intervention effectiveness. The objectives of this study were to evaluate the efficacy of a panel of 10 serological markers as a proxy for malaria exposure and to determine underlying risk factors of seropositivity. We conducted cross-sectional surveys in two sites of contrasting malaria transmission intensities in southwestern Ethiopia: Arjo in Oromia Region (low transmission) and Gambella in Gambella Regional State (moderate transmission). We measured antibody reactivity against six P. falciparum (AMA-1, CSP, EBA175RIII-V, MSP-1 42 , MSP-3, RH2ab) and four P. vivax (DBPII[Sal1], EBP2, MSP-1 19 , RBP2b) targets. We used mixed effects logistic regressions to assess predictors of seropositivity. Plasmodium spp. infection prevalence by quantitative polymerase chain reaction was 1.36% in Arjo and 10.20% in Gambella. Seroprevalence and antibody levels against all 10 antigens were higher in Gambella than in Arjo. We observed spatial heterogeneities in seroprevalence across Arjo and smaller variations across Gambella. Seroprevalence in both sites was lowest against Pf CSP and highest against Pf AMA-1, Pf MSP-1 42 , and Pv MSPS-1 19 . Male sex, age, and agricultural occupation were positively associated with seropositivity in Arjo associations were less pronounced in Gambella. Our findings demonstrate that seroprevalence and antibody levels to specific Plasmodium antigens can be used to identify high-risk groups and geographical areas where interventions to reduce malaria transmission should be implemented.
Publisher: Springer Science and Business Media LLC
Date: 30-09-2020
DOI: 10.1038/S41598-020-73073-5
Abstract: A thorough understanding of malaria vector species composition and their bionomic characteristics is crucial to devise effective and efficient vector control interventions to reduce malaria transmission. It has been well documented in Africa that malaria interventions in the past decade have resulted in major changes in species composition from endophilic Anopheles gambiae to exophilic An. arabiensis . However, the role of cryptic rare mosquito species in malaria transmission is not well known. This study examined the species composition and distribution, with a particular focus on malaria transmission potential of novel, uncharacterized Anopheles cryptic species in western Kenya. Phylogenetic analysis based on ITS2 and COX1 genes revealed 21 Anopheles mosquito species, including two previously unreported novel species. Unusually high rates of Plasmodium sporozoite infections were detected in An. funestus , An. gambiae and eight cryptic rare species. Plasmodium falciparum, P. malariae and P. ovale sporozoite infections were identified with large proportion of mixed species infections in these vectors. This study, for the first time, reports extensive new Anopheles cryptic species involved in the malaria transmission in western Kenya. These findings underscore the importance of non-common Anopheles species in malaria transmission and the need to target them in routine vector control and surveillance efforts.
No related grants have been discovered for Ming-Chieh Lee.