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Abstract Background Evolutionary pressures lead to the selection of efficient malaria vectors either resistant or susceptible to Plasmodium parasites. These forces may favour the introduction of species genotypes that adapt to new breeding habitats, potentially having an impact on malaria transmission. Thioester-containing protein 1 (TEP1) of Anopheles gambiae complex plays an important role in innate immune defenses against parasites. This study aims to characterize the distribution pattern of TEP1 polymorphisms among populations of An. gambiae sensu lato (s.l.) in western Kenya. Methods Anopheles gambiae adult and larvae were collected using pyrethrum spray catches (PSC) and plastic dippers respectively from Homa Bay, Kakamega, Bungoma, and Kisumu counties between 2017 and 2020. Collected adults and larvae reared to the adult stage were morphologically identified and then identified to sibling species by PCR. TEP1 alleles were determined in 627 anopheles mosquitoes using restriction fragment length polymorphisms-polymerase chain reaction (RFLP-PCR) and to validate the TEP1 genotyping results, a representative sample of the alleles was sequenced. Results Two TEP1 alleles (TEP1*S1 and TEP1*R2) and three corresponding genotypes (*S1/S1, *R2/S1, and *R2/R2) were identified. TEP1*S1 and TEP1*R2 with their corresponding genotypes, homozygous *S1/S1 and heterozygous *R2/S1 were widely distributed across all sites with allele frequencies of approximately 80% and 20%, respectively both in Anopheles gambiae and Anopheles arabiensis. There was no significant difference detected among the populations and between the two mosquito species in TEP1 allele frequency and genotype frequency. The overall low levels in population structure (F ST = 0.019) across all sites corresponded to an effective migration index (Nm = 12.571) and low Nei’s genetic distance values (

Background: In Myanmar, civil unrest and the establishment of internally displaced person (IDP) settlements along the Myanmar-China border have impacted malaria transmission.Methods: Microsatellite markers were used to examine source-sink dynamics for Plasmodium vivax between IDP settlements and surrounding villages in the border region. Genotypic structure and diversity were compared across the 3 years following the establishment of IDP settlements, to infer demographic history. We investigated whether human migration and landscape heterogeneity contributed to P. vivax transmission.Results: P. vivax from IDP settlements and local communities consistently exhibited high genetic diversity within populations but low polyclonality within individuals. No apparent genetic structure was observed among populations and years. P. vivax genotypes in China were similar to those in Myanmar, and parasite introduction was unidirectional. Landscape factors, including distance, elevation, and land cover, do not appear to impede parasite gene flow.Conclusions: The admixture of P. vivax genotypes suggested that parasite gene flow via human movement contributes to the spread of malaria both locally in Myanmar and across the international border. Our genetic findings highlight the presence of large P. vivax gene reservoirs that can sustain transmission. Thus, it is important to reinforce and improve existing control efforts along border areas. [ABSTRACT FROM AUTHOR]

Background: The widespread use of indoor-based malaria vector control interventions has been shown to alter the behaviour of vectors in Africa. There is an increasing concern that such changes could sustain residual transmission. This study was conducted to assess vector species composition, feeding behaviour and their contribution to indoor and outdoor malaria transmission in western Kenya. Methods: Anopheles mosquito collections were carried out from September 2015 to April 2016 in Ahero and Iguhu sites, western Kenya using CDC light traps (indoor and outdoor), pyrethrum spray catches (PSCs) (indoor) and pit shelters (outdoor). Species within Anopheles gambiae s.l. and Anopheles funestus s.l. were identified using polymerase chain reaction (PCR). Enzyme-linked immunosorbent assay (ELISA) was used to determine mosquito blood meal sources and sporozoite infections. Results: A total of 10,864 female Anopheles mosquitoes comprising An. gambiae s.l. (71.4%), An. funestus s.l. (12.3%), Anopheles coustani (9.2%) and Anopheles pharoensis (7.1%) were collected. The majority (61.8%) of the anopheline mosquitoes were collected outdoors. PCR result (n = 581) revealed that 98.9% An. arabiensis and 1.1% An. gambiae s.s. constituted An. gambiae s.l. in Ahero while this was 87% An. gambiae s.s. and 13% An. arabiensis in Iguhu. Of the 108 An. funestus s.l. analysed by PCR, 98.1% belonged to An. funestus s.s. and 1.9% to Anopheles leesoni. The human blood index (HBI) and bovine blood index (BBI) of An. arabiensis was 2.5 and 73.1%, respectively. Anopheles gambiae s.s. had HBI and BBI of 50 and 28%, respectively. The HBI and BBI of An. funestus was 60 and 22.3%, respectively. Forage ratio estimate revealed that An. arabiensis preferred to feed on cattle, An. gambiae s.s. showed preference for both human and cattle, while An. funestus preferred human over other hosts. In Ahero, the sporozoite rates for An. arabiensis and An. funestus were 0.16 and 1.8%, respectively, whereas in Iguhu, the sporozoite rates for An. gambiae s.s. and An. funestus were 2.3 and 2.4%, respectively. In Ahero, the estimated indoor and outdoor entomological inoculation rate (EIR) was 108.6 infective bites/person/year (79.0 from An. funestus and 29.6 from An. arabiensis) and 43.5 infective bites/person/year (27.9 from An. arabiensis and 15.6 from An. funestus), respectively. In Iguhu, the estimated indoor and outdoor EIR was 24.5 infective bites/person/year (18.8 from An. gambiae s.s. and 5.7 from An. funestus) and 5.5 infective bites/person/year (all from An. gambiae s.s.), respectively. Conclusion: Anopheles gambiae s.s. showed an increasing tendency to feed on cattle. Anopheles arabiensis was highly zoophagic, whereas An. funestus showed anthropophagic behaviour. While the majority of malaria transmission occurred indoor, the magnitude of outdoor transmission was considerably high. Additional control tools that complement the existing interventions are required to control residual transmission. [ABSTRACT FROM AUTHOR]

Background: Outdoor malaria transmission is becoming an increasingly important problem in malaria control in Africa. Larval control is a promising intervention as it can target both indoor and outdoor biting mosquitoes. However, the currently available biolarvicide formulations have a short effective duration, and consequently larval control incurs a high operational expense due to the requirement for frequent re-treatment of larval habitats. Formulations of biolarvicides with long-lasting effects is highly desired. A recently developed FourStar® slow-release briquet formulation of Bacillus thuringiensis israelensis and Bacillus sphaericus was evaluated to test its efficacy on malaria vectors. Methods: The study evaluated FourStarTM briquets 180-days formulation under semi-natural and natural conditions to test their efficacy in reducing the mosquito population in western Kenya. The semi-natural habitats used the formulation dissolved in rainwater with appropriate concentrations, and second-instar larvae of Anopheles gambiae were introduced and the number of surviving larvae and pupae produced was recorded daily as the outcome. The briquets formulation was then tested in natural habitats for efficacy on pupal productivity reduction in highland and lowland sites in western Kenya. The formulation was finally tested for efficacy in reducing adult mosquito populations in randomized clusters in western Kenya highland. Results: In semi-natural conditions, the FourStarTM briquets 180-days formulation completely inhibited mosquito pupal production in the first 3 months, and then reduced pupal productivity by 87-98% (P < 0.001) 4-6 months after application. In natural habitats, during the first 2 months no pupae were detected from any of the treated habitats in highland sites, and Anopheles spp. pupal density was reduced by 60-90% in the next 3-5 months (P < 0.001). In the lowland site, pupal productivity reduction was 100% in the first 3 months, and 75-90% in the next 4-5 months (P < 0.001). The randomized cluster trial found that the application of the briquets formulation reduced mean densities of indoor-biting mosquitoes by 76-82% (P < 0.001) and by 67-75% (P < 0.001) for outdoor-biting mosquitoes. Conclusion: This study demonstrated that long-lasting biological larviciding was effective in reducing pupal productivity of larval habitats, and reducing indoor and outdoor resting mosquitoes. The study suggests that long-lasting microbial larviciding may be a promising complementary malaria vector control tool and warrants further large-scale evaluation. [ABSTRACT FROM AUTHOR]

Background: Internally displaced persons (IDP) represent vulnerable populations whose public health conditions merit special attention. In the China-Myanmar border area, human movement and resettlements of IDP can influence malaria transmission. Comparison of disease incidence and vector densities between IDP camps and surrounding local villages allows for better understanding of current epidemiology and to evaluate the effectiveness of interventions in the region. Methods: Malaria and vector surveillance was conducted in three IDP camps and three local villages neighbouring the camps along the China-Myanmar border in Myanmar. Clinical malaria cases were collected from seven hospitals/ clinics from April 2011 to December 2014. Malaria vector population dynamics were monitored using CDC light traps. The use of malaria preventive measures and information on aid agencies and their activities was obtained through questionnaire surveys. Results: Malaria was confirmed in 1832 patients. Of these cases, 85.4 % were Plasmodium vivax and 11.4 % were Plasmodium falciparum malaria. Annual malaria incidence rates were 38.8 and 127.0 cases/1000 person year in IDP camps and local villages, respectively. Older children of 5-14 years had the highest incidence rate in the camps regardless of gender, while male adults had significantly higher incidence rates than females in local villages and females childbearing age had significantly lower risk to malaria in IDP camps compare to local villages. Seasonal malaria outbreaks were observed both in the IDP camps and in the local villages from May to August 2013. The proportion of P. vivax remained unchanged in local villages but increased by approximately tenfold in IDP camps from 2011 to 2014. Anopheles vector density was tenfold higher in local villages compared to IDP camps (2.0:0.2 females/trap/night). Over 99 % of households in both communities owned bed nets. While long-lasting insecticidal nets accounted for 61 % of nets used in IDPs, nearly all residents of local villages owned regular nets without insecticide-impregnation. There were more active aid agencies in the camps than in local villages. Conclusion: Malaria in IDP camps was significantly lower than the surrounding villages through effective control management. The observation of P. vivax outbreaks in the study area highlights the need for increased control efforts. Expansion of malaria intervention strategies in IDP camps to local surrounding villages is critical to malaria control in the border area. [ABSTRACT FROM AUTHOR]

Background: The massive scale-up of insecticide-treated nets (ITNs) and indoor residual spraying (IRS) has led to a substantial increase in malaria vector insecticide resistance as well as in increased outdoor transmission, both of which hamper the effectiveness and efficiency of ITN and IRS. Long-lasting microbial larvicide can be a cost-effective new supplemental intervention tool for malaria control.Methods/design: We will implement the long-lasting microbial larvicide intervention in 28 clusters in two counties in western Kenya. We will test FourStar controlled release larvicide (6 % by weight Bacillus thuringiensis israelensis and 1 % Bacillus sphaerius) by applying FourStar controlled release granule formulation, 90-day briquettes, and 180-day briquettes in different habitat types. The primary endpoint is clinical malaria incidence rate and the secondary endpoint is malaria vector abundance and transmission intensity. The intervention will be conducted as a two-step approach. First, we will conduct a four-cluster trial (two clusters per county, with one of the two clusters randomly assigned to the intervention arm) to optimize the larvicide application scheme. Second, we will conduct an open-label, cluster-randomized trial to evaluate the effectiveness and cost-effectiveness of the larvicide. Fourteen clusters in each county will be assigned to intervention (treatment) or no intervention (control) by a block randomization on the basis of clinical malaria incidence, vector density, and human population size per site. We will treat each treatment cluster with larvicide for three rounds at 4-month intervals, followed by no treatment for the following 8 months. Next, we will switch the control and treatment sites. The former control sites will receive three rounds of larvicide treatment at appropriate time intervals, and former treatment sites will receive no larvicide. We will monitor indoor and outdoor vector abundance using CO2-baited CDC light traps equipped with collection bottle rotators. Clinical malaria data will be aggregated from government-run malaria treatment centers.Discussion: Since current first-line vector intervention methods do not target outdoor transmission and will select for higher insecticide resistance, new methods beyond bed nets and IRS should be considered. Long-lasting microbial larviciding represents a promising new tool that can target both indoor and outdoor transmission and alleviate the problem of pyrethroid resistance. It also has the potential to diminish costs by reducing larvicide reapplications. If successful, it could revolutionize malaria vector control in Africa, just as long-lasting bed nets have done.Trial Registration: U.S. National Institute of Health, study ID NCT02392832 . Registered on 3 February 2015. [ABSTRACT FROM AUTHOR]

Background: Epidemiological characteristics of clinical malaria may differ from asymptomatic infections, thus both cross-sectional parasite screening and longitudinal clinical case surveillance are necessary for malaria transmission monitoring and control. Methods: In order to monitor malaria transmission, surveillance of clinical malaria from two years of active case surveillance in three cohorts of 6,750 individuals, asymptomatic parasitaemia cases of 5,300 individuals and clinical cases in three study areas were carried out in the western Kenyan highlands in 2009 and 2010. Age distribution, seasonality and spatial clustering were analysed. Results: The results revealed a significant difference in the age distribution of clinical cases between passive and active case surveillance, and between clinical case rate and asymptomatic parasite rate. The number of reported cases from health facilities significantly underestimated clinical malaria incidence. The increase in asymptomatic parasite prevalence from low to high transmission seasons was significantly higher for infants (

Background: Insecticide-treated bed nets (ITNs) are known to be highly effective in reducing malaria morbidity and mortality. However, usage varies among households, and such variations in actual usage may seriously limit the potential impact of nets and cause spatial heterogeneity on malaria transmission. This study examined ITN ownership and underlying factors for among-household variation in use, and malaria transmission in two highland regions of western Kenya. Methods: Cross-sectional surveys were conducted on ITN ownership (possession), compliance (actual usage among those who own ITNs), and malaria infections in occupants of randomly sampled houses in the dry and the rainy seasons of 2009. Results: Despite ITN ownership reaching more than 71%, compliance was low at 56.3%. The compliance rate was significantly higher during the rainy season compared with the dry season (62% vs. 49.6%). Both malaria parasite prevalence (11.8% vs. 5.1%) and vector densities (1.0 vs.0.4 female/house/night) were significantly higher during the rainy season than during the dry season. Other important factors affecting the use of ITNs include: a household education level of at least primary school level, significantly high numbers of nuisance mosquitoes, and low indoor temperatures. Malaria prevalence in the rainy season was about 30% lower in ITN users than in non-ITN users, but this percentage was not significantly different during the dry season. Conclusion: In malaria hypo-mesoendemic highland regions of western Kenya, the gap between ITNownership and usage is generally high with greater usage recorded during the high transmission season. Because of the low compliance among those who own ITNs, there is a need to sensitize households on sustained use of ITNs in order to optimize their role as a malaria control tool. [ABSTRACT FROM AUTHOR]

Background: Malaria in the western Kenya highlands is characterized by unstable and high transmission variability which results in epidemics during periods of suitable climatic conditions. The sensitivity of a site to malaria epidemics depends on the level of immunity of the human population. This study examined how terrain in the highlands affects exposure and sensitivity of a site to malaria. Methods: The study was conducted in five sites in the western Kenya highlands, two U-shaped valleys (Iguhu, Emutete), two V-shaped valleys (Marani, Fort-Ternan) and one plateau (Shikondi) for 16 months among 6-15 years old children. Exposure to malaria was tested using circum-sporozoite protein (CSP) and merozoite surface protein (MSP) immunochromatographic antibody tests; malaria infections were tested by microscopic examination of thick and thin smears, the children's homes were georeferenced using a global positioning system. Paired t-test was used to compare the mean prevalence rates of the sites, K-function was use to determine if the clustering of malaria infections was significant. Results and Discussion: The mean antibody prevalence was 22.6% in Iguhu, 24% in Emutete, 11.5% in Shikondi, 8.3% in Fort-Ternan and 9.3% in Marani. The mean malaria infection prevalence was 23.3% in Iguhu, 21.9% in Emutete, 4.7% in Shikondi, 2.9% in Fort-Ternan and 2.4% in Marani. There was a significant difference in the antibodies and malaria infection prevalence between the two valley systems, and between the two valley systems and the plateau (P < 0.05). There was no significant difference in the antibodies and malaria infection prevalence in the two U-shaped valleys (Iguhu and Emutete) and in the V-shaped valleys (Marani and Fort Ternan) (P > 0.05). There was 8.5- fold and a 2-fold greater parasite and antibody prevalence respectively, in the U-shaped compared to the V-shaped valleys. The plateau antibody and parasite prevalence was similar to that of the V-shaped valleys. There was clustering of malaria antibodies and infections around flat areas in the U-shaped valleys, the infections were randomly distributed in the V-shaped valleys and less clustered at the plateau. Conclusion: This study showed that the V-shaped ecosystems have very low malaria prevalence and few individuals with an immune response to two major malaria antigens and they can be considered as epidemic hotspots. These populations are at higher risk of severe forms of malaria during hyper-transmission seasons. The plateau ecosystem has a similar infection and immune response to the V-shaped ecosystems. The U-shaped ecosystems are transmission hotspots. [ABSTRACT FROM AUTHOR]

Background: Malaria cases on the highlands west of Mount Kenya have been noticed since 10 - 20 years ago. It was not clear whether these cases were introduced from the nearby lowland or resulted from local transmission because of no record of vector mosquitoes on the highlands. Determination of presence and abundance of malaria vector is vital for effective control and epidemic risk assessment of malaria among both local residents and tourists. Methods: A survey on 31 aquatic sites for the malaria-vector mosquitoes was carried out along the primary road on the highlands around Mount Kenya and the nearby Mwea lowland during April 13 to June 28, 2005. Anopheline larvae were collected and reared into adults for morphological and molecular species identification. In addition, 31 families at three locations of the highlands were surveyed using a questionnaire about their history of malaria cases during the past five to 20 years. Results: Specimens of Anopheles arabiensis were molecularly identified in Karatina and Naro oru on the highlands at elevations of 1,720 - 1,921 m above sea level. This species was also the only malaria vector found in the Mwea lowland. Malaria cases were recorded in the two highland locations in the past 10 years with a trend of increasing. Conclusion: Local malaria transmission on the Mount Kenya highlands is possible due to the presence of An. arabiensis. Land use pattern and land cover might be the key factors affecting the vector population dynamics and the highland malaria transmission in the region. [ABSTRACT FROM AUTHOR]