Malaria vectors in Lake Victoria and adjacent habitats in western Kenya

Non-random distribution of Plasmodium Species infections and associated clinical features in children in the lake Victoria region, Kenya, 2012-2018

BACKGROUND

While Plasmodium falciparum (Pf) stands out as the most lethal malaria parasite species in humans, the impact of other species should not be dismissed. Moreover, there is a notable lack of understanding of mixed-species infections and their clinical implications.

METHODS

We conducted eight school-based cross-sectional malariometric surveys in the Lake Victoria region of western Kenya between January-February 2012 and September-October 2018. In each survey, a minimum of 100 children aged 3 to 15 years were randomly chosen from a school in Ungoye village on the mainland and as well as from each school selected in every catchment area on Mfangano island. Plasmodium infection was determined by microscopy and nested polymerase chain reaction (PCR). The multiple-kind lottery (MKL) model calculated the expected distribution of Plasmodium infections in the population and compared it to observed values using a chi-squared test (χ2).

RESULTS

The Plasmodium prevalence was 25.9% (2521/9724) by microscopy and 51.1% (4969/9724) by PCR. Among all infections detected by PCR, Pf, P. malariae (Pm), and P. ovale (Po) mono-infections were 58.6%, 3.1%, and 1.8%, respectively. Pf/Pm, Pf/Po, Pm/Po, and Pf/Pm/Po co-infections were 23.5%, 4.3%, 0.1%, and 8.6%, respectively. MKL modelling revealed non-random distributions, with frequencies of Pf/Pm and Pf/Pm/Po co-infections being significantly higher than expected (χ2 = 3385.60, p < 0.001). Pf co-infections with Pm and Po were associated with a decreased risk of fever (aOR 0.64, 95% CI 0.46-0.83; p = 0.01) and increased risks of splenomegaly (aOR 12.79, 95% CI 9.69-16.9; p < 0.001) and anaemia (aOR 2.57, 95% CI 2.09-3.15; p < 0.001), compared to single-species infections.

CONCLUSION

This study sheds light on the potential interaction between Pf and Pm and/or Po. Given the clinical significance of mixed-species infections, improved diagnostics, and case management of Pm and Po are urgently needed.

Plasmodium falciparum population dynamics in East Africa and genomic surveillance along the Kenya-Uganda border

East African countries accounted for ~ 10% of all malaria prevalence worldwide in 2022, with an estimated 23.8 million cases and > 53,000 deaths. Despite recent increases in malaria incidence, high-resolution genome-wide analyses of Plasmodium parasite populations are sparse in Kenya, Tanzania, and Uganda. The Kenyan-Ugandan border region is a particular concern, with Uganda confirming the emergence and spread of artemisinin resistant P. falciparum parasites. To establish genomic surveillance along the Kenyan-Ugandan border and analyse P. falciparum population dynamics within East Africa, we generated whole-genome sequencing (WGS) data for 38 parasites from Bungoma, Western Kenya. These sequences were integrated into a genomic analysis of available East African isolate data (n = 599) and revealed parasite subpopulations with distinct genetic structure and diverse ancestral origins. Ancestral admixture analysis of these subpopulations alongside isolates from across Africa (n = 365) suggested potential independent ancestral populations from other major African populations. Within isolates from Western Kenya, the prevalence of biomarkers associated with chloroquine resistance (e.g. Pfcrt K76T) were significantly reduced compared to wider East African populations and a single isolate contained the PfK13 V568I variant, potentially linked to reduced susceptibility to artemisinin. Overall, our work provides baseline WGS data and analysis for future malaria genomic surveillance in the region.

Modeling the shared risks of malaria and anemia in Rwanda

In sub-Saharan Africa, malaria and anemia contribute substantially to the high burden of morbidity and mortality among under-five children. In Rwanda, both diseases have remained public health challenge over the years in spite of the numerous intervention programs and policies put in place. This study aimed at understanding the geographical variations between the joint and specific risks of both diseases in the country while quantifying the effects of some socio-demographic and climatic factors. Using data extracted from Rwanda Demographic and Health Survey, a shared component model was conceived and inference was based on integrated nested Laplace approximation. The study findings revealed similar spatial patterns for the risk of malaria and the shared risks of both diseases, thus confirming the strong link between malaria and anaemia. The spatial patterns revealed that the risks for contracting both diseases are higher among children living in the districts of Rutsiro, Nyabihu, Rusizi, Ruhango, and Gisagara. The risks for both diseases are significantly associated with type of place of residence, sex of household head, ownership of bed net, wealth index and mother's educational attainment. Temperature and precipitation also have substantial association with both diseases. When developing malaria intervention programs and policies, it is important to take into account climatic and environmental variability in Rwanda. Also, potential intervention initiatives focusing on the lowest wealth index, children of uneducated mothers, and high risky regions need to be reinforced.

Biting behaviour, spatio-temporal dynamics, and the insecticide resistance status of malaria vectors in different ecological zones in Ghana

BACKGROUND

A significant decrease in malaria morbidity and mortality has been attained using long-lasting insecticide-treated nets and indoor residual spraying. Selective pressure from these control methods influences changes in vector bionomics and behavioural pattern. There is a need to understand how insecticide resistance drives behavioural changes within vector species. This study aimed to determine the spatio-temporal dynamics and biting behaviour of malaria vectors in different ecological zones in Ghana in an era of high insecticide use for public health vector control.

METHODS

Adult mosquitoes were collected during the dry and rainy seasons in 2017 and 2018 from five study sites in Ghana in different ecological zones. Indoor- and outdoor-biting mosquitoes were collected per hour from 18:00 to 06:00 h employing the human landing catch (HLC) technique. Morphological and molecular species identifications of vectors were done using identification keys and PCR respectively. Genotyping of insecticide-resistant markers was done using the TaqMan SNP genotyping probe-based assays. Detection of Plasmodium falciparum sporozoites was determined using PCR.

RESULTS

A total of 50,322 mosquitoes belonging to four different genera were collected from all the study sites during the sampling seasons in 2017 and 2018. Among the Anophelines were Anopheles gambiae s.l. 93.2%, (31,055/33,334), An. funestus 2.1%, (690/33,334), An. pharoensis 4.6%, (1545/33,334), and An. rufipes 0.1% (44/33,334). Overall, 76.4%, (25,468/33,334) of Anopheles mosquitoes were collected in the rainy season and 23.6%, (7866/33,334) in the dry season. There was a significant difference (Z = 2.410; P = 0.0160) between indoor-biting (51.1%; 15,866/31,055) and outdoor-biting An. gambiae s.l. (48.9%; 15,189/31,055). The frequency of the Vgsc-1014F mutation was slightly higher in indoor-biting mosquitoes (54.9%) than outdoors (45.1%). Overall, 44 pools of samples were positive for P. falciparum CSP giving an overall sporozoite rate of 0.1%.

CONCLUSION

Anopheles gambiae s.l. were more abundant indoors across all ecological zones of Ghana. The frequency of G119S was higher indoors than outdoors from all the study sites, but with higher sporozoite rates in outdoor mosquitoes in Dodowa and Kpalsogu. There is, therefore, an urgent need for a supplementary malaria control intervention to control outdoor-biting mosquitoes.

Effective population size of Culex quinquefasciatus under insecticide-based vector management and following Hurricane Harvey in Harris County, Texas

Introduction: Culex quinquefasciatus is a mosquito species of significant public health importance due to its ability to transmit multiple pathogens that can cause mosquito-borne diseases, such as West Nile fever and St. Louis encephalitis. In Harris County, Texas, Cx. quinquefasciatus is a common vector species and is subjected to insecticide-based management by the Harris County Public Health Department. However, insecticide resistance in mosquitoes has increased rapidly worldwide and raises concerns about maintaining the effectiveness of vector control approaches. This concern is highly relevant in Texas, with its humid subtropical climate along the Gulf Coast that provides suitable habitat for Cx. quinquefasciatus and other mosquito species that are known disease vectors. Therefore, there is an urgent and ongoing need to monitor the effectiveness of current vector control programs. Methods: In this study, we evaluated the impact of vector control approaches by estimating the effective population size of Cx. quinquefasciatus in Harris County. We applied Approximate Bayesian Computation to microsatellite data to estimate effective population size. We collected Cx. quinquefasciatus samples from two mosquito control operation areas; 415 and 802, during routine vector monitoring in 2016 and 2017. No county mosquito control operations were applied at area 415 in 2016 and 2017, whereas extensive adulticide spraying operations were in effect at area 802 during the summer of 2016. We collected data for eighteen microsatellite markers for 713 and 723 mosquitoes at eight timepoints from 2016 to 2017 in areas 415 and 802, respectively. We also investigated the impact of Hurricane Harvey's landfall in the Houston area in August of 2017 on Cx. quinquefasciatus population fluctuation. Results: We found that the bottleneck scenario was the most probable historical scenario describing the impact of the winter season at area 415 and area 802, with the highest posterior probability of 0.9167 and 0.4966, respectively. We also detected an expansion event following Hurricane Harvey at area 802, showing a 3.03-fold increase in 2017. Discussion: Although we did not detect significant effects of vector control interventions, we found considerable influences of the winter season and a major hurricane on the effective population size of Cx. quinquefasciatus. The fluctuations in effective population size in both areas showed a significant seasonal pattern. Additionally, the significant population expansion following Hurricane Harvey in 2017 supports the necessity for post-hurricane vector-control interventions.

Human NCR3 gene variants rs2736191 and rs11575837 alter longitudinal risk for development of pediatric malaria episodes and severe malarial anemia

BACKGROUND

Plasmodium falciparum malaria is a leading cause of pediatric morbidity and mortality in holoendemic transmission areas. Severe malarial anemia [SMA, hemoglobin (Hb) < 5.0 g/dL in children] is the most common clinical manifestation of severe malaria in such regions. Although innate immune response genes are known to influence the development of SMA, the role of natural killer (NK) cells in malaria pathogenesis remains largely undefined. As such, we examined the impact of genetic variation in the gene encoding a primary NK cell receptor, natural cytotoxicity-triggering receptor 3 (NCR3), on the occurrence of malaria and SMA episodes over time.

METHODS

Susceptibility to malaria, SMA, and all-cause mortality was determined in carriers of NCR3 genetic variants (i.e., rs2736191:C > G and rs11575837:C > T) and their haplotypes. The prospective observational study was conducted over a 36 mos. follow-up period in a cohort of children (n = 1,515, aged 1.9-40 mos.) residing in a holoendemic P. falciparum transmission region, Siaya, Kenya.

RESULTS

Poisson regression modeling, controlling for anemia-promoting covariates, revealed a significantly increased risk of malaria in carriers of the homozygous mutant allele genotype (TT) for rs11575837 after multiple test correction [Incidence rate ratio (IRR) = 1.540, 95% CI = 1.114-2.129, P = 0.009]. Increased risk of SMA was observed for rs2736191 in children who inherited the CG genotype (IRR = 1.269, 95% CI = 1.009-1.597, P = 0.041) and in the additive model (presence of 1 or 2 copies) (IRR = 1.198, 95% CI = 1.030-1.393, P = 0.019), but was not significant after multiple test correction. Modeling of the haplotypes revealed that the CC haplotype had a significant additive effect for protection against SMA (i.e., reduced risk for development of SMA) after multiple test correction (IRR = 0.823, 95% CI = 0.711-0.952, P = 0.009). Although increased susceptibility to SMA was present in carriers of the GC haplotype (IRR = 1.276, 95% CI = 1.030-1.581, P = 0.026) with an additive effect (IRR = 1.182, 95% CI = 1.018-1.372, P = 0.029), the results did not remain significant after multiple test correction. None of the NCR3 genotypes or haplotypes were associated with all-cause mortality.

CONCLUSIONS

Variation in NCR3 alters susceptibility to malaria and SMA during the acquisition of naturally-acquired malarial immunity. These results highlight the importance of NK cells in the innate immune response to malaria.

Profiles of bacterial communities and environmental factors associated with proliferation of malaria vector mosquitoes within the Kenyan Coast

Background

Since Anopheles mosquitoes which transmit and maintain the malaria parasite breed in the outdoor environment, there is an urgent need to manage these mosquito breeding sites. In order to elaborate more on the ecological landscape of mosquito breeding sites, the bacterial community structure and their interactions with physicochemical factors in mosquito larval habitats was characterised in Kwale County (Kenya), where malaria is endemic.

Methods

The physical characteristics and water physicochemical parameters of the habitats were determined and recorded. Water samples were also collected from the identified sites for total metagenomic DNA extraction in order to characterise the bacterial communities within the breeding sites.

Results and Discussion

Sites where mosquito larvae were found were described as positive and those without mosquito larvae as negative. Electrical conductivity, total dissolved solids, salinity and ammonia were lower in the rainy season than in the dry season, which also coincided with a high proportion of positive sites. Pseudomonadota was the most common phyla recovered in all samples followed by Bacteroidota and then Actinomycetota. The presence or absence of mosquito larvae in a potential proliferation site was not related to the bacterial community structure in the sampled sites, but was positively correlated with bacterial richness and evenness.

Conclusion

Generally, the presence of Anopheles mosquito larvae was found to be positively correlated with rainy season, bacterial richness and evenness, and negatively correlated with electrical conductivity, total dissolved solids, salinity and ammonia. The findings of this study have implications for predicting the potential of environmental water samples to become mosquito proliferation sites.

Diversity of Anopheles species and zoonotic malaria vector of the Buton Utara Wildlife Sanctuary, Southeast Sulawesi, Indonesia

BACKGROUND

The recent deforestation for agricultural, mining, and human re-settlement has significantly reduced the habitat of many non-human primates (NHPs) in Indonesia and intensifies interaction between the NHPs and humans and thus opening the possibility of pathogen spill-over. The emergence of zoonotic malaria, such as Plasmodium knowlesi, poses an immense threat to the current malaria control and elimination that aims for the global elimination of malaria by 2030. As malaria in humans and NHPs is transmitted by the female Anopheles mosquito, malaria vector control is very important to mitigate the spill-over of the malaria parasite to humans. The present study aims to explore the Anopheles species diversity in human settlements adjacent to the wildlife sanctuary forest in Buton Utara Regency, Southeast Sulawesi, Indonesia, and identify the species that potentially transmit the pathogen from monkey to human in the area.

METHODS

Mosquito surveillance was conducted using larval and adult collection, and the collected mosquitoes were identified morphologically and molecularly using the barcoding markers, cytochrome oxidase subunit I (COI), and internal transcribed species 2 (ITS2) genes. Plasmodium sporozoite carriage was conducted on mosquitoes collected through human landing catch (HLC) and human-baited double net trap (HDNT).

RESULTS

The results revealed several Anopheles species, such as Anopheles flavirostris (16.6%), Anopheles sulawesi (3.3%), Anopheles maculatus (3.3%), Anopheles koliensis (1.2%), and Anopheles vagus (0.4%). Molecular analysis of the sporozoite carriage using the primate-specific malaria primers identified An. sulawesi, a member of the Leucosphyrus group, carrying Plasmodium inui sporozoite.

CONCLUSIONS

This study indicates that the transmission of zoonotic malaria in the area is possible and alerts to the need for mitigation efforts through a locally-tailored vector control intervention and NHPs habitat conservation.

Drug resistance profiling of asymptomatic and low-density Plasmodium falciparum malaria infections on Ngodhe island, Kenya, using custom dual-indexing next-generation sequencing

Malaria control initiatives require rapid and reliable methods for the detection and monitoring of molecular markers associated with antimalarial drug resistance in Plasmodium falciparum parasites. Ngodhe island, Kenya, presents a unique malaria profile, with lower P. falciparum incidence rates than the surrounding region, and a high proportion of sub-microscopic and low-density infections. Here, using custom dual-indexing and Illumina next generation sequencing, we generate resistance profiles on seventy asymptomatic and low-density P. falciparum infections from a mass drug administration program implemented on Ngodhe island between 2015 and 2016. Our assay encompasses established molecular markers on the Pfcrt, Pfmdr1, Pfdhps, Pfdhfr, and Pfk13 genes. Resistance markers for sulfadoxine-pyrimethamine were identified at high frequencies, including a quintuple mutant haplotype (Pfdhfr/Pfdhps: N51I, C59R, S108N/A437G, K540E) identified in 62.2% of isolates. The Pfdhps K540E biomarker, used to inform decision making for intermittent preventative treatment in pregnancy, was identified in 79.2% of isolates. Several variants on Pfmdr1, associated with reduced susceptibility to quinolones and lumefantrine, were also identified (Y184F 47.1%; D1246Y 16.0%; N86 98%). Overall, we have presented a low-cost and extendable approach that can provide timely genetic profiles to inform clinical and surveillance activities, especially in settings with abundant low-density infections, seeking malaria elimination.

Environmental and socio-economic determinants of the occurrence of malaria clusters in Colombia

This study identifies the environmental and socio-economic determinants of clusters of high malaria incidence in Colombia during the period of 2008-2019. The malaria cases were obtained from the National System of Surveillance in Public Health, with 798,897 cases reported in the 986 Colombian municipalities evaluated during the study period. Spatial autocorrelation of incidence was examined with global and local indices. Clusters were identified in the Amazon, Pacific, and Uraba-Bajo Cauca-Alto Sinú regions. The factors associated with a municipality belonging to a high-incidence cluster were identified using a logistic regression model with mixed effects and showed a positive association for the variables (forest coverage and minimum multi-year average rainfall). An inverse relationship was observed for aqueduct coverage and the odds of belonging to a cluster. A 1% increase in forest coverage was associated with a 4.2% increase in the odds of belonging to a malaria cluster. The association with minimum multi-year average rainfall was positive (OR = 1.0011; 95% CI 1.0005-1.0027). A 1% increase in aqueduct coverage was associated with a 4.3% decrease in the odds of belonging to malaria cluster. The identification of malaria cluster determinants in Colombia could help guide surveillance and disease control policies.

Altitude, not potential larval habitat availability, explains pronounced variation in Plasmodium falciparum infection prevalence in the western Kenya highlands

Progress in malaria control has stalled over the recent years. Knowledge on main drivers of transmission explaining small-scale variation in prevalence can inform targeted control measures. We collected finger-prick blood samples from 3061 individuals irrespective of clinical symptoms in 20 clusters in Busia in western Kenya and screened for Plasmodium falciparum parasites using qPCR and microscopy. Clusters spanned an altitude range of 207 meters (1077-1284 m). We mapped potential mosquito larval habitats and determined their number within 250 m of a household and distances to households using ArcMap. Across all clusters, P. falciparum parasites were detected in 49.8% (1524/3061) of individuals by qPCR and 19.5% (596/3061) by microscopy. Across the clusters, prevalence ranged from 26% to 70% by qPCR. Three to 34 larval habitats per cluster and 0-17 habitats within a 250m radius around households were observed. Using a generalized linear mixed effect model (GLMM), a 5% decrease in the odds of getting infected per each 10m increase in altitude was observed, while the number of larval habitats and their proximity to households were not statistically significant predictors for prevalence. Kitchen located indoors, open eaves, a lower level of education of the household head, older age, and being male were significantly associated with higher prevalence. Pronounced variation in prevalence at small scales was observed and needs to be taken into account for malaria surveillance and control. Potential larval habitat frequency had no direct impact on prevalence.

Shared component modelling of early childhood anaemia and malaria in Kenya, Malawi, Tanzania and Uganda

Background

Malaria and anaemia contribute substantially to child morbidity and mortality. In this study, we sought to jointly model the residual spatial variation in the likelihood of these two correlated diseases, while controlling for individual-level, household-level and environmental characteristics.

Methods

A child-level shared component model was utilised to partition shared and disease-specific district-level spatial effects.

Results

The results indicated that the spatial variation in the likelihood of malaria was more prominent compared to that of anaemia, for both the shared and specific spatial components. In addition, approximately 30% of the districts were associated with an increased likelihood of anaemia but a decreased likelihood of malaria. This suggests that there are other drivers of anaemia in children in these districts, which warrants further investigation.

Conclusions

The maps of the shared and disease-specific spatial patterns provide a tool to allow for more targeted action in malaria and anaemia control and prevention, as well as for the targeted allocation of limited district health system resources.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12887-022-03694-4.

A novel statistical framework for exploring the population dynamics and seasonality of mosquito populations

Understanding the temporal dynamics of mosquito populations underlying vector-borne disease transmission is key to optimizing control strategies. Many questions remain surrounding the drivers of these dynamics and how they vary between species-questions rarely answerable from individual entomological studies (that typically focus on a single location or species). We develop a novel statistical framework enabling identification and classification of time series with similar temporal properties, and use this framework to systematically explore variation in population dynamics and seasonality in anopheline mosquito time series catch data spanning seven species, 40 years and 117 locations across mainland India. Our analyses reveal pronounced variation in dynamics across locations and between species in the extent of seasonality and timing of seasonal peaks. However, we show that these diverse dynamics can be clustered into four 'dynamical archetypes', each characterized by distinct temporal properties and associated with a largely unique set of environmental factors. Our results highlight that a range of environmental factors including rainfall, temperature, proximity to static water bodies and patterns of land use (particularly urbanicity) shape the dynamics and seasonality of mosquito populations, and provide a generically applicable framework to better identify and understand patterns of seasonal variation in vectors relevant to public health.

High Blood Parasite Infection Rate and Low Fitness Suggest That Forest Water Bodies Comprise Ecological Traps for Pied Flycatchers

Blood parasites are considered to have strong negative effects on host fitness. Negative fitness consequences may be associated with proximity to areas where blood parasite vectors reproduce. This study tested for relationships between haemosporidian infection prevalence, parasitemia, and fitness parameters of breeding Pied Flycatchers (Ficedula hypoleuca) at different distances from forest water bodies. Prevalence and parasitemias (the intensity of infection) of haemosporidians and vector abundance generally decreased with increasing distance from forest lakes, streams, and bogs. Fledgling numbers were lower, and their condition was worse in the vicinity of water bodies, compared with those located one kilometer away from lakes and streams. At the beginning of the breeding season, adult body mass was not related to distance to the nearest water body, whereas at the end of the breeding season body mass was significantly lower closer to water bodies. Forest areas around water bodies may represent ecological traps for Pied Flycatchers. Installing nest boxes in the vicinity of forest water bodies creates unintended ecological traps that may have conservation implications.

Grass-like plants release general volatile cues attractive for gravid Anopheles gambiae sensu stricto mosquitoes

Background

Understanding the ecology and behaviour of disease vectors, including the olfactory cues used to orient and select hosts and egg-laying sites, are essential for the development of novel, insecticide-free control tools. Selected graminoid plants have been shown to release volatile chemicals attracting malaria vectors; however, whether the attraction is selective to individual plants or more general across genera and families is still unclear.

Methods

To contribute to the current evidence, we implemented bioassays in two-port airflow olfactometers and in large field cages with four live graminoid plant species commonly found associated with malaria vector breeding sites in western Kenya: Cyperus rotundus and C. exaltatus of the Cyperaceae family, and Panicum repens and Cynodon dactylon of the Poaceae family. Additionally, we tested one Poaceae species, Cenchrus setaceus, not usually associated with water. The volatile compounds released in the headspace of the plants were identified using gas chromatography/mass spectrometry.

Results

All five plants attracted gravid vectors, with the odds of a mosquito orienting towards the choice-chamber with the plant in an olfactometer being 2–5 times higher than when no plant was present. This attraction was maintained when tested with free-flying mosquitoes over a longer distance in large field cages, though at lower strength, with the odds of attracting a female 1.5–2.5 times higher when live plants were present than when only water was present in the trap. Cyperus rotundus, previously implicated in connection with an oviposition attractant, consistently elicited the strongest response from gravid vectors. Volatiles regularly detected were limonene, β-pinene, β-elemene and β-caryophyllene, among other common plant compounds previously described in association with odour-orientation of gravid and unfed malaria vectors.

Conclusions

The present study confirms that gravid Anopheles gambiae sensu stricto use chemical cues released from graminoid plants to orientate. These cues are released from a variety of graminoid plant species in both the Cyperaceae and Poaceae family. Given the general nature of these cues, it appears unlikely that they are exclusively used for the location of suitable oviposition sites. The utilization of these chemical cues for attract-and-kill trapping strategies must be explored under natural conditions to investigate their efficiency when in competition with complex interacting natural cues.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04939-4.

Characterizing the genomic variation and population dynamics of Plasmodium falciparum malaria parasites in and around Lake Victoria, Kenya

Characterising the genomic variation and population dynamics of Plasmodium falciparum parasites in high transmission regions of Sub-Saharan Africa is crucial to the long-term efficacy of regional malaria elimination campaigns and eradication. Whole-genome sequencing (WGS) technologies can contribute towards understanding the epidemiology and structural variation landscape of P. falciparum populations, including those within the Lake Victoria basin, a region of intense transmission. Here we provide a baseline assessment of the genomic diversity of P. falciparum isolates in the Lake region of Kenya, which has sparse genetic data. Lake region isolates are placed within the context of African-wide populations using Illumina WGS data and population genomic analyses. Our analysis revealed that P. falciparum isolates from Lake Victoria form a cluster within the East African parasite population. These isolates also appear to have distinct ancestral origins, containing genome-wide signatures from both Central and East African lineages. Known drug resistance biomarkers were observed at similar frequencies to those of East African parasite populations, including the S160N/T mutation in the pfap2mu gene, which has been associated with delayed clearance by artemisinin-based combination therapy. Overall, our work provides a first assessment of P. falciparum genetic diversity within the Lake Victoria basin, a region targeting malaria elimination.

Urban malaria in sub-Saharan Africa: dynamic of the vectorial system and the entomological inoculation rate

Sub-Saharan Africa is registering one of the highest urban population growth across the world. It is estimated that over 75% of the population in this region will be living in urban settings by 2050. However, it is not known how this rapid urbanization will affect vector populations and disease transmission. The present study summarizes findings from studies conducted in urban settings between the 1970s and 2020 to assess the effects of urbanization on the entomological inoculation rate pattern and anopheline species distribution. Different online databases such as PubMed, ResearchGate, Google Scholar, Google were screened. A total of 90 publications were selected out of 1527. Besides, over 200 additional publications were consulted to collate information on anopheline breeding habitats and species distribution in urban settings. The study confirms high malaria transmission in rural compared to urban settings. The study also suggests that there had been an increase in malaria transmission in most cities after 2003, which could also be associated with an increase in sampling, resources and reporting. Species of the Anopheles gambiae complex were the predominant vectors in most urban settings. Anopheline larvae were reported to have adapted to different aquatic habitats. The study provides updated information on the distribution of the vector population and the dynamic of malaria transmission in urban settings. The study also highlights the need for implementing integrated control strategies in urban settings.

An increasing role of pyrethroid-resistant Anopheles funestus in malaria transmission in the Lake Zone, Tanzania

Anopheles funestus is playing an increasing role in malaria transmission in parts of sub-Saharan Africa, where An. gambiae s.s. has been effectively controlled by long-lasting insecticidal nets. We investigated vector population bionomics, insecticide resistance and malaria transmission dynamics in 86 study clusters in North-West Tanzania. An. funestus s.l. represented 94.5% (4740/5016) of all vectors and was responsible for the majority of malaria transmission (96.5%), with a sporozoite rate of 3.4% and average monthly entomological inoculation rate (EIR) of 4.57 per house. Micro-geographical heterogeneity in species composition, abundance and transmission was observed across the study district in relation to key ecological differences between northern and southern clusters, with significantly higher densities, proportions and EIR of An. funestus s.l. collected from the South. An. gambiae s.l. (5.5%) density, principally An. arabiensis (81.1%) and An. gambiae s.s. (18.9%), was much lower and closely correlated with seasonal rainfall. Both An. funestus s.l. and An. gambiae s.l. were similarly resistant to alpha-cypermethrin and permethrin. Overexpression of CYP9K1, CYP6P3, CYP6P4 and CYP6M2 and high L1014S-kdr mutation frequency were detected in An. gambiae s.s. populations. Study findings highlight the urgent need for novel vector control tools to tackle persistent malaria transmission in the Lake Region of Tanzania.

Long-Lasting Insecticidal Nets Incorporating Piperonyl Butoxide Reduce the Risk of Malaria in Children in Western Kenya: A Cluster Randomized Controlled Trial

Malaria vectors have acquired an enzyme that metabolizes pyrethroids. To tackle this problem, we evaluated long-lasting insecticidal nets incorporating piperonyl butoxide (PBO-LLINs) with a community-based cluster randomized control trial in western Kenya. The primary endpoints were anopheline density and Plasmodium falciparum polymerase chain reaction (PCR)-positive prevalence (PCRpfPR) of children aged 7 months to 10 years. Four clusters were randomly selected for each of the treatment and control arms (eight clusters in total) from 12 clusters, and PBO-LLINs and standard LLINs were distributed in February 2011 to 982 and 1,028 houses for treatment and control arms, respectively. Entomological surveys targeted 20 houses in each cluster, and epidemiological surveys targeted 150 children. Cluster-level permutation tests evaluated the effectiveness using the fitted values from individual level regression models adjusted for baseline. Bootstrapping estimated 95% confidence intervals (CIs). The medians of anophelines per house were 1.4 (interquartile range [IQR]: 2.3) and 3.4 (IQR: 3.7) in the intervention and control arms after 3 months, and 0.4 (IQR: 0.2) and 1.6 (IQR: 0.5) after 10 months, respectively. The differences were -2.5 (95% CI: -6.4 to -0.6) and -1.3 (95% CI: -2.0 to -0.7), respectively. The datasets of 861 and 775 children were analyzed in two epidemiological surveys. The median PCRpfPRs were 25% (IQR: 11%) in the intervention arm and 52% (IQR: 11%) in the control arm after 5 months and 33% (IQR: 11%) and 45% (IQR: 5%) after 12 months. The PCRpfPR ratios were 0.67 (95% CI: 0.38, 0.91) and 0.74 (95% CI: 0.53, 0.90), respectively. We confirmed the superiority of PBO-LLINs.

Evaluation of malaria preventive measures among adult patients attending the Bamendjou and Foumbot district hospitals of the West Region of Cameroon

BACKGROUND

Although a significant decrease in entomological and epidemiological indicators was reported in Cameroon since the introduction of insecticide-treated bed nets, malaria prevalence remains high also in some parts of the West Region of Cameroon. This study was designed to evaluate malaria preventive measures among patients attending the Bamendjou and Foumbot District hospitals of the West Region of Cameroon.

METHODS

This was a cross-sectional study carried out within a period of 3 months, from January to March 2020. Data was obtained using a structured questionnaire and laboratory analysis. The CareStart™ Pf Malaria HRP2 qualitative rapid diagnostic test was used for malaria diagnosis. The questionnaire was designed to collect information on respondent's socio-demographic characteristics, and the use of malaria preventive measures. Data were analysed using descriptive statistics, regression analysis, and Chi-square (and Fisher's exact) test.

RESULTS

A total of 170 study participants were recruited in Foumbot and 197 in Bamendjou. Malaria was significantly (P < 0.0001) more prevalent in Foumbot (47.06%) than in Bamendjou (19.8%). In Foumbot, non-use of insect repellent spray (P = 0.0214), insect repellent body cream (P = 0.0009), mosquito spray (P = 0.0001) and not draining stagnant water (P = 0.0004) predisposed to higher risk of malaria. In Bamendjou, non-use of insect repellent spray (P = 0.0012), long-lasting insecticidal bed nets (P = 0.0001), window and door nets (P = 0.0286), predisposed to a higher risk of malaria.

CONCLUSIONS

Malaria prevalence was high among the study participants especially in Foumbot. An adequate follow-up to ensure effective execution of the recently launched third phase of LLINs distribution campaign in Cameroon is recommended. Additionally, integrated vector management is required to ensure effective control of malaria transmission in Foumbot and Bamendjou.

A preliminary study on designing a cluster randomized control trial of two new mosquito nets to prevent malaria parasite infection

BACKGROUND

Although long-lasting insecticidal nets (LLINs) are the most effective tool for preventing malaria parasite transmission, the nets have some limitations. For example, the increase of LLIN use has induced the rapid expansion of mosquito insecticide resistance. More than two persons often share one net, which increases the infection risk. To overcome these problems, two new mosquito nets were developed, one incorporating piperonyl butoxide and another covering ceilings and open eaves. We designed a cluster randomized controlled trial (cRCT) to evaluate these nets based on the information provided in the present preliminary study.

RESULTS

Nearly 75% of the anopheline population in the study area in western Kenya was Anopheles gambiae s. l., and the remaining was Anopheles funestus s. l. More female anophelines were recorded in the western part of the study area. The number of anophelines increased with rainfall. We planned to have 80% power to detect a 50% reduction in female anophelines between the control group and each intervention group. The between-cluster coefficient of variance was 0.192. As the number of clusters was limited to 4 due to the size of the study area, the estimated cluster size was 7 spray catches with an alpha of 0.05. Of 1619 children tested, 626 (48%) were Plasmodium falciparum positive using a rapid diagnostic test (RDT). The prevalence was higher in the northwestern part of the study area. The number of children who slept under bed nets was 929 (71%). The P. falciparum RDT-positive prevalence (RDTpfPR) of net users was 45%, and that of non-users was 55% (OR 0.73; 95% CI 0.56, 0.95). Using 45% RDTpfPR of net users, we expected each intervention to reduce prevalence by 50%. The intracluster correlation coefficient was 0.053. With 80% power and an alpha of 0.05, the estimated cluster size was 116 children. Based on the distribution of children, we modified the boundaries of the clusters and established 300-m buffer zones along the boundaries to minimize a spillover effect.

CONCLUSIONS

The cRCT study design is feasible. As the number of clusters is limited, we will apply a two-stage procedure with the baseline data to evaluate each intervention.

Harmful Algal Blooms Threaten the Health of Peri-Urban Fisher Communities: A case study in Kisumu Bay, Lake Victoria, Kenya

Available guidance to mitigate health risks from exposure to freshwater harmful algal blooms (HABs) is largely derived from temperate ecosystems. Yet in tropical ecosystems, HABs can occur year-round, and resource-dependent populations face multiple routes of exposure to toxic components. Along Winam Gulf, Lake Victoria, Kenya, fisher communities rely on lake water contaminated with microcystins (MCs) from HABs. In these peri-urban communities near Kisumu, we tested hypotheses that MCs exceed exposure guidelines across seasons, and persistent HABs present a chronic risk to fisher communities through ingestion with minimal water treatment and frequent, direct contact. We tested source waters at eleven communities across dry and rainy seasons from September 2015 through May 2016. We measured MCs, other metabolites, physicochemical parameters, chlorophyll a, phytoplankton abundance and diversity, and fecal indicators. We then selected four communities for interviews about water sources, usage, and treatment. Greater than 30% of source water samples exceeded WHO drinking water guidelines for MCs (1μg/L), and over 60% of source water samples exceeded USEPA guidelines for children and immunocompromised individuals. 50% of households reported sole use of raw lake water for drinking and household use, with alternate sources including rain and boreholes. Household chlorination was the most widespread treatment utilized. At this tropical, eutrophic lake, HABs pose a year-round health risk for fisher communities in resource -limited settings. Community-based solutions and site-specific guidance for Kisumu Bay and similarly impacted regions is needed to address a chronic health exposure likely to increase in severity and duration with global climate change.

A cross-sectional observational study investigating the association between sedges (swamp grasses, Cyperaceae) and the prevalence of immature malaria vectors in aquatic habitats along the shore of Lake Victoria, western Kenya

Background: Strategies that involve manipulations of the odour-orientation of gravid malaria vectors could lead to novel attract-and-kill interventions. Recent work has highlighted the potential involvement of graminoid plants in luring vectors to oviposition sites. This study aimed to analyse the association between water-indicating graminoid plants (Cyperaceae, sedges), other abiotic and biotic factors and the presence and abundance of early instar Anopheles larvae in aquatic habitats as a proxy indicator for oviposition.

Methods: A cross-sectional survey of 110 aquatic habitats along the shores of Lake Victoria was done during the rainy season. Habitats were sampled for mosquito larvae using the sweep-net method and habitat characteristics recorded.

Results: Anopheles arabiensis was the dominant species identified from aquatic habitats. Larvae of the secondary malaria vectors such as Anopheles coustani, An. rufipes and An. maculipalpis were found only in habitats covered with graminoids, whereas An. arabiensis, An. ziemanni and An. pharoensis were found in both habitats with and without graminoid plants. The hypothesis that sedges might be positively associated with the presence and abundance of early instar Anopheles larvae could not be confirmed. The dominant graminoid plants in the habitats were Panicum repens, Cynodon dactylon in the Poaceae family and Cyperus rotundus in the Cyperaceae family. All of these habitats supported abundant immature vector populations. The presence of early instar larvae was significantly and positively associated with swamp habitat types (OR=22, 95% CI=6-86, P<0.001) and abundance of late Anopheles larvae (OR=359, CI=33-3941, P<0.001), and negatively associated with the presence of tadpoles (OR=0.1, CI=0.0.01-0.5, P=0.008).

Conclusions: Early instar malaria vectors were abundant in habitats densely vegetated with graminoid plants in the study area but no specific preference could be detected for any species or family. In search for oviposition cues, it might be useful to screen for chemical volatiles released from all dominant plant species.

Prevalence of and factors associated with malaria in children under five years of age in Malawi, using malaria indicator survey data

BACKGROUND

Malaria remains a public health problem in developing countries and Malawi is no different. Although there has been an improvement in reducing malaria in Malawi, it remains a problem, especially in children less than five years old. The primary objective of the study was to assess whether socio-economic, geographic and demographic factors are associated with malaria, using the generalized additive mixed model (GAMM).

DATA AND METHODOLOGY

The study used a 2017 dataset from the Malawi Malaria Indicator Survey (MMI) with a total number of 2724 children under five years old. The study also utilized the GAMM to analyze data. The outcome was that either the child had malaria or did not, as detected using the malaria Rapid Diagnostic Test (RDT) (Ayele et al., 2014a).

RESULTS

In this study, more than 37 % of the total number of children who were tested showed a positive malaria result. In addition, the results from this study using GAMM indicated that anaemia, mother's education level, wealth index, child's age, the altitude of the place of residence, region, place of residence, toilet facility and electricity were significantly associated with a positive malaria RDT.

CONCLUSION

The study revealed that socio-economic, geographical and demographic variables are the key factors in improving malaria vectors in children. Improving income levels and supporting the poorer rural community mostly from the Central Region would be a great achievement in reducing malaria vectors in Malawi. In addition, improving health care in rural areas, especially at higher altitudes, would contribute to controlling malaria and reducing anaemia.

Impact of Insecticide Resistance on P. falciparum Vectors' Biting, Feeding, and Resting Behaviour in Selected Clusters in Teso North and South Subcounties in Busia County, Western Kenya

INTRODUCTION

Behavioural resistance to insecticides restrains the efficacy of vector control tools against mosquito-transmitted diseases. The current study is aimed at determining the impact of insecticide resistance on major malaria vectors' biting, feeding, and resting behaviour in areas with and areas without insecticide resistance in Teso North and Teso South, Busia County, Western Kenya.

METHODS

Mosquito larvae were sampled using a dipper, reared into 3-5-day-old female mosquitoes [4944] which were exposed to 0.75% permethrin and 0.05% deltamethrin using World Health Organization tube assay method. Blood meal, species identification, and kdr Eastgene PCRs were also performed on adult mosquitoes sampled using mosquito collection methods [3448]. Biting, feeding, resting, and exiting behaviours of field-collected mosquitoes from five selected clusters were analysed.

RESULTS

The lowest Kdr genotypic frequency (SS) proportion was found in female Anophelines collected in Kengatunyi at 58% while Rwatama had the highest genotypic frequency at 93%, thus susceptible and resistant clusters, respectively. The peak hour for mosquito seeking a human bite was between 0300 and 0400 hrs in the resistant cluster and 0400-0500 hrs in the susceptible cluster. The heterozygous mosquitoes maintained the known 2100-2200 hrs peak hour. There was a higher proportion of homozygous susceptible vectors (86.4%) seeking humans indoor than outdoor bitters (78.3%). Mosquito blood meals of human origin were 60% and 87% in susceptible Kengatunyi and resistant Rwatama cluster, respectively. There was significant difference between homozygous-resistant vectors feeding on human blood compared to homozygous susceptible mosquitoes (p ≤ 0.05). The proportion of bovine blood was highest in the susceptible cluster. A higher proportion of homozygous-resistant anophelines were feeding and resting indoors. No heterozygous mosquito was found resting indoor while 4.2% of the mosquitoes were caught while exiting the house through the window. Discussion. A shift in resistant Anopheles gambiae sl highest peak hour of aggressiveness from 2100-2200 hrs to 0300-0400 hrs is a key change in its biting pattern. Due to the development of resistance, mosquitoes no longer have to compete against the time the human host enters into the formerly lethal chemical and or physical barrier in the form of long-lasting insecticide-treated net. No heterozygous LS mosquito rested indoors possibly due to disadvantages of heterozygosity which could have increased their fitness costs as well as energy costs in the presence of the insecticidal agents in the treated nets. Conclusions and recommendations. Out of bed biting by female mosquitoes and partial susceptibility may contribute to residual malaria transmission. Insecticide-resistant vectors have become more endophagic and anthropophillic. Hence, insecticidal nets, zooprophylaxis, and novel repellents are still useful chemical, biological, and physical barriers against human blood questing female mosquitoes. Further studies should be done on genetic changes in mosquitoes and their effects on changing mosquito behaviour.

Characterizing the Spatial Determinants and Prevention of Malaria in Kenya

The United Nations' Sustainable Development Goal 3 is to ensure health and well-being for all at all ages with a specific target to end malaria by 2030. Aligned with this goal, the primary objective of this study is to determine the effectiveness of utilizing local spatial variations to uncover the statistical relationships between malaria incidence rate and environmental and behavioral factors across the counties of Kenya. Two data sources are used-Kenya Demographic and Health Surveys of 2000, 2005, 2010, and 2015, and the national Malaria Indicator Survey of 2015. The spatial analysis shows clustering of counties with high malaria incidence rate, or hot spots, in the Lake Victoria region and the east coastal area around Mombasa; there are significant clusters of counties with low incidence rate, or cold spot areas in Nairobi. We apply an analysis technique, geographically weighted regression, that helps to better model how environmental and social determinants are related to malaria incidence rate while accounting for the confounding effects of spatial non-stationarity. Some general patterns persist over the four years of observation. We establish that variables including rainfall, proximity to water, vegetation, and population density, show differential impacts on the incidence of malaria in Kenya. The El-Nino-southern oscillation (ENSO) event in 2015 was significant in driving up malaria in the southern region of Lake Victoria compared with prior time-periods. The applied spatial multivariate clustering analysis indicates the significance of social and behavioral survey responses. This study can help build a better spatially explicit predictive model for malaria in Kenya capturing the role and spatial distribution of environmental, social, behavioral, and other characteristics of the households.

Targeting remaining pockets of malaria transmission in Kenya to hasten progress towards national elimination goals: an assessment of prevalence and risk factors in children from the Lake endemic region

BACKGROUND

With an overall decline of malaria incidence, elimination of malaria is gradually becoming the next target for many of countries affected by the disease. In Kenya the national malaria control strategy is aiming to reach pre-elimination for most parts of the country. However, considerable heterogeneity in prevalence of the disease within the country and especially the remaining high prevalent region of the Lake endemic region is likely to slow progress towards this target. To achieve a sustained control and an eventual elimination, a clear understanding of drivers of ongoing malaria transmission in remaining hotspots is needed.

METHODS

Data from the 2015 Malaria Indicator Survey (MIS) were analysed for prevalence of malaria parasitaemia in children (6 months to 14 years) of different countries within the highly endemic Lake region. Univariate and multivariate logistic regression analysis were preformed to explore associations between selected risk factors and being parasitaemic. A predictive model was built for the association between malaria and the risk factors with the aim of identifying heterogeneities of the disease at the lower administrative levels.

RESULTS

Overall, 604/2253 (27%, 95% CI 21.8-32.2) children were parasitaemic. The highest prevalence was observed in Busia County (37%) and lowest in Bungoma County (18%). Multivariate logistic regression analysis showed that the 10-14 years age group (OR = 3.0, 95% CI 2.3-4.1), households in the poorest socio-economic class (OR = 2.1, 95% CI 1.3-3.3), farming (OR = 1.4, 95% CI 1.2-2.5) and residence in Busia (OR = 4.6, 95% CI 2.1-8.2), Kakamega (OR = 2.6, 95% CI 1.3-5.4), and Migori counties (OR = 4.6 95% CI 2.1-10.3) were associated with higher risk of parasitaemia. Having slept under a long-lasting insecticide-treated bed net (LLIN) was associated with a lower risk (OR = 0.7, 95% CI 0.6-0.9). No association were found between malaria infection and the gender of the child, the household head, and the education status of the household head.

DISCUSSION AND CONCLUSION

Detailed analysis of malaria prevalence data in a hotspot area can identify new threats and avail opportunities for directing intervention. In the Lake endemic region of Kenya, interventions should be focused more on counties with the highest prevalence, and should target older children as well as children from the lower socio-economic strata. Precisely targeting interventions in remaining hotspots and high-risk populations will likely make impact and accelerate progress towards pre-elimination targets.

Mosquitoes of Etiological Concern in Kenya and Possible Control Strategies

Kenya is among the most affected tropical countries with pathogen transmitting Culicidae vectors. For decades, insect vectors have contributed to the emergence and distribution of viral and parasitic pathogens. Outbreaks and diseases have a great impact on a country's economy, as resources that would otherwise be used for developmental projects are redirected to curb hospitalization cases and manage outbreaks. Infected invasive mosquito species have been shown to increasingly cross both local and global boarders due to the presence of increased environmental changes, trade, and tourism. In Kenya, there have been several mosquito-borne disease outbreaks such as the recent outbreaks along the coast of Kenya, involving chikungunya and dengue. This certainly calls for the implementation of strategies aimed at strengthening integrated vector management programs. In this review, we look at mosquitoes of public health concern in Kenya, while highlighting the pathogens they have been linked with over the years and across various regions. In addition, the major strategies that have previously been used in mosquito control and what more could be done to reduce or combat the menace caused by these hematophagous vectors are presented.

Artisanal fishing supports breeding of malaria mosquitoes in Western Kenya

BACKGROUND

Everyday hundreds of people, mainly men, set out to take part in a vibrant artisanal capture fishing (ACF) industry on Lake Victoria. It is not known whether actions of artisanal fishers, in their unrelenting quest for existence, surpass ecosystems' sustainability thresholds with potentially negative repercussions on human health with respect to malaria transmission potential. This article sought to fill this information gap.

METHODS

This study used an ecosystem approach to find out how ACF processes facilitate the breeding of mosquitoes. The observational study adopted a cross-sectional design and was carried out on Mageta Island situated inside Lake Victoria in western Kenya.

RESULTS

Of the 87 mosquito larval habitats identified 27 (31%) were created through ACF activities. The ACF-related habitats, hereafter collectively referred to as 'fishing habitats', included fishing boats (24), trenches (1) and fish bait mines (2). About half (48%) of Anopheles larvae were recovered from fishing habitats. The mean larval density in the fishing habitats (35.7 ± 1.15) was double that in non-fishing habitats (17.4 ± 0.539). Despite being the most common 'non-fishing habitat' type (N = 32), the mean number of Anopheles larvae present in rock pools (30.81 ± 10.54) was significantly less than those found inside fishing boats (N = 24; 40.08 ± 10.16). Overall, man-made habitats and those used to support livelihoods contained significantly more Anopheles larvae.

CONCLUSIONS

These data show that artisanal capture fishing is a key driver of malaria epidemiology on Mageta Island. This suggests that larval source management strategies in the global south should pay attention to the heterogeneity in Anopheles breeding habitats created through livelihood activities.

Evaluating community’s knowledge on integrated malaria, schistosomiasis and soil transmitted helminth (STH) infections in a Lake Victoria island, Kenya: A mixed method approach

Background: The burden of malaria, schistosomiasis and soil transmitted helminthes (STH) in the islands of Lake Victoria, Kenya, poses a considerable public health challenge. Although many studies have been conducted on the co-infection arising from these parasites, few have evaluated communities’ knowledge of the same. Increasing the level of knowledge about a disease or preventive chemotherapy is important, but efforts need to be focused on community perception and understanding of the problem so as to encourage engagement with the proposed control measures. This study aimed at understanding a community’s knowledge of malaria, schistosomiasis and STH in Lake Victoria island where an integrated preventive chemotherapy intervention was implemented. Methods: This study was conducted in Ngodhe Island in Lake Victoria in Homa Bay County, western Kenya region between April and May 2016. The study adopted a mixed method approach where both qualitative and quantitative data collection was performed concurrently.  Results: A total of 239 people participated in this study. All the respondents reported that they had heard about malaria, 89.1% had heard about schistosomiasis while 87.4% had heard about STH. The majority of the respondents (93.3%) drew their drinking water directly from the lake and 80.3% reported bathing in the lake. Out of all the respondents, 96.2% knew about the ongoing preventive chemotherapy. Most respondents (94.1%) said they would participate in a preventive chemotherapy again, while 0.4% was not sure. The majority of the respondents (86.6%) reported that integrated strategy is the most effective approach to control the three infections in the Island. Conclusion: The findings show a very high knowledge about these diseases. Although this study found majority of the respondents are aware of the co-infection of malaria, schistosomiasis and STH, their behaviors such as bathing in the lake exacerbates the problem.

Behavioral responses of gravid Culex quinquefasciatus, Aedes aegypti, and Anopheles quadrimaculatus mosquitoes to aquatic macrophyte volatiles

Mosquitoes use many cues to assess whether a habitat is conducive for reproduction, possibly including the presence of stimuli from aquatic macrophytes. The effect of water infusions of water hyacinth (Eichhornia crassipes), water lettuce (Pista stratioles), parrotfeather (Myriophyllum aquaticum), and water pennywort (Hydrocotyle umbellata) on mosquito oviposition and attraction was investigated. Gravid Culex quinquefasciatus deposited significantly more egg rafts in water hyacinth, water lettuce, or Bermuda hay (positive control) infusions compared to water, while water pennywort and parrotfeather infusions did not differ from water. In-flight attraction responses of Cx. quinquefasciatus, Aedes aegypti, and Anopheles quadrimaculatus were evaluated. The strongest attraction of gravid Cx. quinquefasciatus and Ae. aegypti occurred in the presence of volatiles from infusions of water hyacinth and water lettuce, which were equal in attractiveness to hay infusion. Water pennywort and parrotfeather infusions were not attractive. Gravid An. quadrimaculatus were not attracted to aquatic plant volatiles. The results suggest that water hyacinth and water lettuce emit volatile chemicals that attract two of three mosquito species tested and stimulate oviposition by Cx. quinquefasciatus, demonstrating that the level of attraction of aquatic plant volatiles varies among species in ways that may have relevance to bait-based detection and control methods.

Dry season occurrence of Anopheles mosquitoes and implications in Jabi Tehnan District, West Gojjam Zone, Ethiopia

Background

Generating evidence on the dry season occurrence of the larval and adult stages of Anopheles mosquitoes helps to design effective malaria vector control strategy as the populations of the vectors is expected to be low.

Methods

Larval and adult stages of Anopheles were surveyed during dry seasons in Mender Meter, Jiga Yehlmidar and Wongie Berkegn villages, Jabi Tehnan District, West Gojjam Zone, Ethiopia. Larvae were surveyed (along the available surface water collections), sampled, identified into genus, counted and late instars of the genus Anopheles identified into species. Indoor-resting adult mosquitoes were collected using insecticide aerosol spray, processed and identified into species. Data was analysed using SPSS version 20.0 to determine frequencies, mean differences and associations.

Results

A total of 3127 Anopheles larvae were collected among which most (91.7%; 2869/3127) were from streams followed by ponds (4.3%; 136/3127) and swamps (3.9%; 122/3127). Anopheles gambiae sensu lato was the most prevalent (84.9%; 921/1085) followed by Anopheles cinereus (7.0%; 76/1085), Anopheles chrysti (3.7%; 40/1085), Anopheles demeilloni (2.8%; 30/1085) and Anopheles rhodesiensis (1.6%; 18/1085). The mean number (mean = 15.3) of An. gambiae from Jiga Yehlmidar was significantly (p = 0.024) higher than the corresponding number (mean = 3.2) from Mender Meter. The mean number (mean = 36.3) of An. gambiae larvae in April 2017 was significantly (p = 0.001) higher than the number (mean = 4.0) in December 2013 and the number (mean = 2.6) in March 2013. A total of 1324 adult Anopheles were collected of which the highest proportion (79.1%; 1048/1324) was An. gambiae, followed by An. chrysti (11.7%; 155/1324), An. demeilloni (6%; 80/1324), An. cinereus (2.6%; 35/1324) and Anopheles coustani (0.5%; 6/1324). The highest proportion (54.3%; 569/1048) of the An. gambiae was collected from Wongie Berkegn followed by Jiga Yehlmidar (23.6%; 247/1048) and Mender Meter (22.1%; 232/1048). The mean number (mean = 7.8) of adult An. gambiae caught in Wongie Berkegn was significantly (p = 0.018) higher compared to the number (mean = 3.0) in Mender Meter. No significant difference was observed in the mean number of adult An. gambiae between the seasons.

Conclusion and implication

Streams were prolific breeding habitats of Anopheles mosquitoes followed by ponds and swamps in the dry seasons. In addition, a high population of indoor resting An. gambiae was caught from indoors. This implies the need for a strengthened vector control during dry seasons using breeding habitat management and improved housing in addition to the existing insecticide (LLINs and IRS) based interventions in Jabi Tehnan District, West Gojjam Zone, Ethiopia.

Antimalarial bednet protection of children disappears when shared by three or more people in a high transmission setting of western Kenya

A sizeable proportion of households is forced to share single long-lasting insecticide treated net (LLIN). However, the relationship between increasing numbers of people sharing a net and the risk for Plasmodium infection is unclear. This study revealed whether risk for Plasmodium falciparum infection is associated with the number of people sharing a LLIN in a holoendemic area of Kenya. Children ⩽5 years of age were tested for P. falciparum infection using polymerase chain reaction. Of 558 children surveyed, 293 (52.5%) tested positive for parasitaemia. Four hundred and fifty-eight (82.1%) reported sleeping under a LLIN. Of those, the number of people sharing a net with the sampled child ranged from 1 to 5 (median = 2). Children using a net alone or with one other person were at lower risk than non-users (OR = 0.29, 95% CI 0.10-0.82 and OR = 0.47, 95% CI 0.22-0.97, respectively). On the other hand, there was no significant difference between non-users and children sharing a net with two (OR = 0.88, 95% CI 0.44-1.77) or more other persons (OR = 0.75, 95% CI 0.32-1.72). LLINs are effective in protecting against Plasmodium infection in children when used alone or with one other person compared with not using them. Public health professionals should inform caretakers of the risks of too many people sharing a net.

Nationwide insecticide resistance status and biting behaviour of malaria vector species in the Democratic Republic of Congo

Background

Globally, the Democratic Republic of Congo (DRC) accounted for 9% of malaria cases and 10% of malaria deaths in 2015. As part of control efforts, more than 40 million long-lasting insecticidal nets (LLINs) were distributed between 2008 and 2013, resulting in 70% of households owning one or more LLINs in 2014. To optimize vector control efforts, it is critical to monitor vector behaviour and insecticide resistance trends. Entomological data was collected from eight sentinel sites throughout DRC between 2013 and 2016 in Kingasani, Mikalayi, Lodja, Kabondo, Katana, Kapolowe, Tshikaji and Kalemie. Mosquito species present, relative densities and biting times were monitored using human landing catches (HLC) conducted in eight houses, three times per year. HLC was conducted monthly in Lodja and Kapolowe during 2016 to assess seasonal dynamics. Laboratory data included resistance mechanism frequency and sporozoite rates. Insecticide susceptibility testing was conducted with commonly used insecticides including deltamethrin and permethrin. Synergist bioassays were conducted with PBO to determine the role of oxidases in permethrin resistance.

Results

In Lodja, monthly Anopheles gambiae s.l. biting rates were consistently high at > 10 bites/person/night indoors and outdoors. In Kapolowe, An. gambiae s.l. dominated during the rainy season, and Anopheles funestus s.l. during the dry season. In all sites, An. gambiae and An. funestus biting occurred mostly late at night. In Kapolowe, significant biting of both species started around 19:00, typically before householders use nets. Sporozoite rates were high, with a mean of 4.3% (95% CI 3.4–5.2) for An. gambiae and 3.3% (95% CI 1.3–5.3) for An. funestus. Anopheles gambiae were resistant to permethrin in six out of seven sites in 2016. In three sites, susceptibility to deltamethrin was observed despite high frequency permethrin resistance, indicating the presence of pyrethroid-specific resistance mechanisms. Pre-exposure to PBO increased absolute permethrin-associated mortality by 24%, indicating that resistance was partly due to metabolic mechanisms. The kdr-1014F mutation in An. gambiae was present at high frequency (> 70%) in three sites (Kabondo, Kingasani and Tshikaji), and lower frequency (< 20%) in two sites (Lodja and Kapolowe).

Conclusion

The finding of widespread resistance to permethrin in DRC is concerning and alternative insecticides should be evaluated.

Electronic supplementary material

The online version of this article (10.1186/s12936-018-2285-6) contains supplementary material, which is available to authorized users.

Sweet attraction: sugarcane pollen-associated volatiles attract gravid Anopheles arabiensis

BACKGROUND

Anopheles arabiensis is a key vector for the transmission of human malaria in sub-Saharan Africa. Over the past 10,000 years, humans have successfully cultivated grasses and altered the landscape, creating An. arabiensis favourable environments that contain excellent habitats for both larvae and adults. Sugarcane is the most expanding agricultural system in sub-Saharan Africa, and is linked to the increased threat of malaria in rural communities. The prolific production and wind dispersal of sugarcane pollen, together with standing pools of water, often provide, as a result of irrigation, a nutrient-rich environment for the offspring of gravid malaria mosquitoes.

RESULTS

In the present study, sugarcane pollen-associated volatiles from two cultivars are shown to attract gravid An. arabiensis in a still air two-port olfactometer and stimulate egg laying in an oviposition bioassay. Through combined gas chromatography and electroantennographic detection, as well as combined gas chromatography and mass spectrometric analyses, we identified the bioactive volatiles and generated a synthetic blend that reproduced the full behavioural repertoire of gravid mosquitoes in the Y-tube assay. Two subtractive odour blends, when compared with the full blend, were significantly more attractive. These three and four-component subtractive blends share the compounds (1R)-(+)-α-pinene, nonanal and benzaldehyde, of which, (1R)-(+)-α-pinene and nonanal are found in the attractive odour blends from rice plants and maize pollen. In pairwise comparisons, the rice synthetic odour blend was more attractive to gravid mosquitoes than either of the pollen blends, whereas the pollen blends did not differ in attraction.

CONCLUSIONS

The attraction of gravid females to sugarcane pollen volatiles demonstrated in this study, together with the previously found grass-associated volatiles, raise the potential of developing a bioactive chimeric blend to attract gravid malaria mosquitoes. This is discussed in relation to the development of novel and cost-effective vector control measures.

Spatial distribution and habitat characterization of mosquito species during the dry season along the Mara River and its tributaries, in Kenya and Tanzania

Background

Vector-borne diseases are increasingly becoming a major health problem among communities living along the major rivers of Africa. Although larger water bodies such as lakes and dams have been extensively researched, rivers and their tributaries have largely been ignored. This study sought to establish the spatial distribution of mosquito species during the dry season and further characterize their habitats along the Mara River and its tributaries.

Methods

In this cross-sectional survey, mosquito larvae were sampled along the Mara River, its two perennial tributaries (Amala and Nyangores), drying streams, and adjacent aquatic habitats (e.g. swamps, puddles that receive direct sunlight [open sunlit puddles], rock pools, hippo and livestock hoof prints, and vegetated pools). Each habitat was dipped 20 times using a standard dipper. Distance between breeding sites and human habitation was determined using global positioning system coordinates. The collected mosquito larvae were identified using standard taxonomic keys. Water physico-chemical parameters were measured in situ using a multiparameter meter. Mean mosquito larvae per habitat type were compared using analysis of variance and chi-square tests, while the relationship between mosquito larvae and physico-chemical parameters was evaluated using a generalized linear mixed model. The Cox-Stuart test was used to detect trends of mosquito larvae distribution. The test allowed for verification of monotonic tendency (rejection of null hypothesis of trend absence) and its variability.

Results

A total of 4001 mosquito larvae were collected, of which 2712 (67.8%) were collected from river/stream edge habitats and 1289 (32.2%) were sampled from aquatic habitats located in the terrestrial ecosystem about 50 m away from the main river/streams. Anopheles gambiae s.s, An. arabiensis, and An. funestus group, the three most potent vectors of malaria in Sub-Saharan Africa, together with other anopheline mosquitoes, were the most dominant mosquito species (70.3%), followed by Culex quinquefasciatus and Cx. pipiens complex combined (29.5%). Drying streams accounted for the highest number of larvae captured compared to the other habitat types. A stronger relationship between mosquito larvae abundance and dissolved oxygen (Z = 7.37, P ≤ 0.001), temperature (Z = 7.65, P ≤ 0.001), turbidity (Z = −5.25, P ≤ 0.001), and distance to the nearest human habitation (Z = 4.57, P ≤ 0.001), was observed.

Conclusions

Presence of malaria and non-malaria mosquito larvae within the Mara River basin calls for immediate action to curtail the insurgence of vector-borne diseases within the basin. A vector control program should be conducted during the dry period, targeting drying streams shown to produce the highest number of larval mosquitoes.

Electronic supplementary material

The online version of this article (10.1186/s40249-017-0385-0) contains supplementary material, which is available to authorized users.

Use of epidemiological and entomological tools in the control and elimination of malaria in Ethiopia

Malaria is the leading public health problem in Ethiopia where over 75% of the land surface is at risk with varying intensities depending on altitude and season. Although the mortality because of malaria infection has declined much during the last 15–20 years, some researchers worry that this success story may not be sustainable. Past notable achievements in the reduction of malaria disease burden could be reversed in the future. To interrupt, or even to eliminate malaria transmission in Ethiopia, there is a need to implement a wide range of interventions that include insecticide-treated bed nets, indoor residual spraying, improved control of residual malaria transmission, and improved diagnostics, enhanced surveillance, and methods to deal with the emergence of resistance both to drugs and to insecticides. Developments during the past years with increasing awareness about the role of very low levels of malaria prevalence can sustain infections, may also demand that tools not used in the routine control efforts to reduce or eliminate malaria, should now be made available in places where malaria transmission occurs.

Composition of Anopheles mosquitoes, their blood-meal hosts, and Plasmodium falciparum infection rates in three islands with disparate bed net coverage in Lake Victoria, Kenya

Background

Small islands serve as potential malaria reservoirs through which new infections might come to the mainland and may be important targets in malaria elimination efforts. This study investigated malaria vector species diversity, blood-meal hosts, Plasmodium infection rates, and long-lasting insecticidal net (LLIN) coverage on Mageta, Magare and Ngodhe Islands of Lake Victoria in western Kenya, a region where extensive vector control is implemented on the mainland.

Results

From trapping for six consecutive nights per month (November 2012 to March 2015) using CDC light traps, pyrethrum spray catches and backpack aspiration, 1868 Anopheles mosquitoes were collected. Based on their cytochrome oxidase I (COI) and intergenic spacer region PCR and sequencing, Anopheles gambiae s.l. (68.52%), Anopheles coustani (19.81%) and Anopheles funestus s.l. (11.67%) mosquitoes were differentiated. The mean abundance of Anopheles mosquitoes per building per trap was significantly higher (p < 0.001) in Mageta than in Magare and Ngodhe. Mageta was also the most populated island (n = 6487) with low LLIN coverage of 62.35% compared to Ngodhe (n = 484; 88.31%) and Magare (n = 250; 98.59%). Overall, 416 (22.27%) engorged Anopheles mosquitoes were analysed, of which 41 tested positive for Plasmodium falciparum infection by high-resolution melting (HRM) analysis of 18S rRNA and cytochrome b PCR products. Plasmodium falciparum infection rates were 10.00, 11.76, 0, and 18.75% among blood-fed An. gambiae s.s. (n = 320), Anopheles arabiensis (n = 51), An. funestus s.s. (n = 29), and An. coustani (n = 16), respectively. Based on HRM analysis of vertebrate cytochrome b, 16S rRNA and COI PCR products, humans (72.36%) were the prominent blood-meal hosts of malaria vectors, but 20.91% of blood-meals were from non-human vertebrate hosts.

Conclusions

These findings demonstrate high Plasmodium infection rates among the primary malaria vectors An. gambiae s.s. and An. arabiensis, as well as in An. coustani for the first time in the region, and that non-human blood-meal sources play an important role in their ecology. Further, the higher Anopheles mosquito abundances on the only low LLIN coverage island of Mageta suggests that high LLIN coverage has been effective in reducing malaria vector populations on Magare and Ngodhe Islands.

Characterization and productivity profiles of Aedes aegypti (L.) breeding habitats across rural and urban landscapes in western and coastal Kenya

Background

Aedes aegypti, the principal vector for dengue and other emerging arboviruses, breeds preferentially in various man-made and natural container habitats. In the absence of vaccine, epidemiological surveillance and vector control remain the best practices for preventing dengue outbreaks. Effective vector control depends on a good understanding of larval and adult vector ecology of which little is known in Kenya. In the current study, we sought to characterize breeding habitats and establish container productivity profiles of Ae. aegypti in rural and urban sites in western and coastal Kenya.

Methods

Twenty sentinel houses in each of four study sites (in western and coastal Kenya) were assessed for immature mosquito infestation once a month for a period of 24 months (June 2014 to May 2016). All water-holding containers in and around the households were inspected for Ae. aegypti larvae and pupae.

Results

Collections were made from a total of 22,144 container visits: Chulaimbo (7575) and Kisumu (8003) in the west, and from Msambweni (3199) and Ukunda (3367) on the coast. Of these, only 4–5.6% were positive for Ae. aegypti immatures. In all four sites, significantly more positive containers were located outdoors than indoors. A total of 17,537 Ae. aegypti immatures were sampled from 10 container types. The most important habitat types were buckets, drums, tires, and pots, which produced over 75% of all the pupae. Key outdoor containers in the coast were buckets, drums and tires, which accounted for 82% of the pupae, while pots and tires were the only key containers in the western region producing 70% of the pupae. Drums, buckets and pots were the key indoor containers, producing nearly all of the pupae in the coastal sites. No pupae were collected indoors in the western region. The coastal region produced significantly more Ae. aegypti immatures than the western region both inside and outside the sentinel houses.

Conclusions

These results indicate that productive Ae. aegypti larval habitats are abundant outdoors and that only a few containers produce a majority of the pupae. Although the numbers were lower, productive habitats were detected within households. Targeting source reduction efforts towards these productive containers both inside and outside homes is likely to be a cost-effective way to reduce arboviral transmission in these regions.

Geographical distributions of African malaria vector sibling species and evidence for insecticide resistance

Background

Many of the mosquito species responsible for malaria transmission belong to a sibling complex; a taxonomic group of morphologically identical, closely related species. Sibling species often differ in several important factors that have the potential to impact malaria control, including their geographical distribution, resistance to insecticides, biting and resting locations, and host preference. The aim of this study was to define the geographical distributions of dominant malaria vector sibling species in Africa so these distributions can be coupled with data on key factors such as insecticide resistance to aid more focussed, species-selective vector control.

Results

Within the Anopheles gambiae species complex and the Anopheles funestus subgroup, predicted geographical distributions for Anopheles coluzzii, An. gambiae (as now defined) and An. funestus (distinct from the subgroup) have been produced for the first time. Improved predicted geographical distributions for Anopheles arabiensis, Anopheles melas and Anopheles merus have been generated based on records that were confirmed using molecular identification methods and a model that addresses issues of sampling bias and past changes to the environment. The data available for insecticide resistance has been evaluated and differences between sibling species are apparent although further analysis is required to elucidate trends in resistance.

Conclusions

Sibling species display important variability in their geographical distributions and the most important malaria vector sibling species in Africa have been mapped here for the first time. This will allow geographical occurrence data to be coupled with species-specific data on important factors for vector control including insecticide resistance. Species-specific data on insecticide resistance is available for the most important malaria vectors in Africa, namely An. arabiensis, An. coluzzii, An. gambiae and An. funestus. Future work to combine these data with the geographical distributions mapped here will allow more focussed and resource-efficient vector control and provide information to greatly improve and inform existing malaria transmission models.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-017-1734-y) contains supplementary material, which is available to authorized users.

The role of grass volatiles on oviposition site selection by Anopheles arabiensis and Anopheles coluzzii

Background

The reproductive success and population dynamics, of Anopheles malaria mosquitoes is strongly influenced by the oviposition site selection of gravid females. Mosquitoes select oviposition sites at different spatial scales, starting with selecting a habitat in which to search. This study utilizes the association of larval abundance in the field with natural breeding habitats, dominated by various types of wild grasses, as a proxy for oviposition site selection by gravid mosquitoes. Moreover, the role of olfactory cues emanating from these habitats in the attraction and oviposition stimulation of females was analysed.

Methods

The density of Anopheles larvae in breeding sites associated with Echinochloa pyramidalis, Echinochloa stagnina, Typha latifolia and Cyperus papyrus, was sampled and the larvae identified to species level. Headspace volatile extracts of the grasses were collected and used to assess behavioural attraction and oviposition stimulation of gravid Anopheles arabiensis and Anopheles coluzzii mosquitoes in wind tunnel and two-choice oviposition assays, respectively. The ability of the mosquitoes to differentiate among the grass volatile extracts was tested in multi-choice tent assays.

Results

Anopheles arabiensis larvae were the most abundant species found in the various grass-associated habitats. The larval densities described a hierarchical distribution, with Poaceae (Echinochloa pyramidalis and Echinochloa stagnina)-associated habitat sites demonstrating higher densities than that of Typha-associated sites, and where larvae were absent from Cyperus-associated sites. This hierarchy was maintained by gravid An. arabiensis and An. coluzzii mosquitoes in attraction, oviposition and multi-choice assays to grass volatile extracts.

Conclusions

The demonstrated hierarchical preference of gravid An. coluzzii and An. arabiensis for grass volatiles indicates that vegetation cues associated with larval habitats are instrumental in the oviposition site choice of the malaria mosquitoes. Identifying volatile cues from grasses that modulate gravid malaria mosquito behaviours has distinct potential for the development of tools to be used in future monitoring and control methods.

High and Heterogeneous Prevalence of Asymptomatic and Sub-microscopic Malaria Infections on Islands in Lake Victoria, Kenya

Kenya is intensifying its national efforts in malaria control to achieve malaria elimination. Detailed characterization of malaria infection among populations living in the areas where the disease is endemic in Kenya is a crucial priority, especially for planning and evaluating future malaria elimination strategy. This study aimed to investigate the distribution and extent of malaria infection on islands in Lake Victoria of Kenya to aid in designing new interventions for malaria elimination. Five cross-sectional surveys were conducted between January 2012 and August 2014 on four islands (Mfangano, Takawiri, Kibuogi and Ngodhe) in Lake Victoria and a coastal mainland (Ungoye). Malaria prevalence varied significantly among settings: highest in Ungoye, followed by the large island of Mfangano and lowest in the three remaining small islands. Of the 3867 malaria infections detected by PCR, 91.8% were asymptomatic, 50.3% were sub-microscopic, of which 94% were also asymptomatic. We observed geographical differences and age dependency in both proportion of sub-microscopic infections and asymptomatic parasite carriage. Our findings highlighted the local heterogeneity in malaria prevalence on islands and a coastal area in Lake Victoria, and provided support for the inclusion of mass drug administration as a component of the intervention package to eliminate malaria on islands.

Genetic Diversity and Population Structure of Plasmodium falciparum in Lake Victoria Islands, A Region of Intense Transmission

Understanding the genetic structure and transmission dynamics of Plasmodium falciparum parasites in malaria-endemic regions is crucial before the implementation of interventions. Located in a high-transmission region of western Kenya where P. falciparum is the predominant species, the Lake Victoria islands are ideal for feasibility of malaria elimination studies. We analyzed genetic variation in eight microsatellite loci to examine parasite population structure and gene flow patterns across five sites. High levels of genetic diversity were measured throughout the region (mean heterozygosity index = 0.84). The overall fixation index value between the sites was 0.044, indicating that approximately 5% of the overall allelic variation is due to differences between the populations. Based on these results, we concluded that parasite population structure in the studied islands is shaped by human migration patterns that maintain extensive parasite gene flow between the sites. Consequently, any malaria elimination and interventions strategies in the study area will have to be carried out broadly on all four islands and adjoining mainland region.

Composition and Genetic Diversity of Mosquitoes (Diptera: Culicidae) on Islands and Mainland Shores of Kenya's Lakes Victoria and Baringo

The Lake Baringo and Lake Victoria regions of Kenya are associated with high seroprevalence of mosquito-transmitted arboviruses. However, molecular identification of potential mosquito vector species, including morphologically identified ones, remains scarce. To estimate the diversity, abundance, and distribution of mosquito vectors on the mainland shores and adjacent inhabited islands in these regions, we collected and morphologically identified adult and immature mosquitoes and obtained the corresponding sequence variation at cytochrome c oxidase 1 (COI) and internal transcribed spacer region 2 (ITS2) gene regions. A total of 63 species (including five subspecies) were collected from both study areas, 47 of which have previously been implicated as disease vectors. Fourteen species were found only on island sites, which are rarely included in mosquito diversity surveys. We collected more mosquitoes, yet with lower species composition, at Lake Baringo (40,229 mosquitoes, 32 species) than at Lake Victoria (22,393 mosquitoes, 54 species). Phylogenetic analysis of COI gene sequences revealed Culex perexiguus and Cx tenagius that could not be distinguished morphologically. Most Culex species clustered into a heterogeneous clade with closely related sequences, while Culex pipiens clustered into two distinct COI and ITS2 clades. These data suggest limitations in current morphological identification keys. This is the first DNA barcode report of Kenyan mosquitoes. To improve mosquito species identification, morphological identifications should be supported by their molecular data, while diversity surveys should target both adults and immatures. The diversity of native mosquito disease vectors identified in this study impacts disease transmission risks to humans and livestock.

Risk factors of malaria in children under the age of five years old in Uganda

BACKGROUND

Malaria is the leading cause of morbidity in Uganda with 90-95 % of the population at risk and it contributing to approximately 13 % of under-five mortality. The aim of this study was to investigate the relationship between the malaria status of children under the age of 5 years old in Uganda and selected socio-economic, demographic and environmental factors, as well as to identify significant risk factors associated with malaria.

METHODS

This study made use of data collected from the 2014 Malaria Indicator Survey conducted in Uganda. Two test procedures for malaria in children under the age of 5 years old were carried out. Due to the complex survey design, a generalized linear mixed model was used to test for associations between several independent variables and the response variable, which was whether a child tested positive or negative for malaria according to the microscopy test.

RESULTS

The sample in this study was made up of 4939 children. Of those children, 974 tested positive for malaria, resulting in an observed malaria prevalence of 19.7 %. The socio-economic factors closely related to the risk of malaria were main floor material, main wall material and availability of electricity in the household. The event of indoor residual spraying (IRS) significantly reduced a child's risk of malaria. An older child was associated with a higher risk of malaria, however their risk decreased with an increase in cluster altitude and an increase in their caregiver's education level.

CONCLUSION

Although there has been a significant increase in the use of mosquito nets since the previous Malaria Indicator Survey done in 2009, particularly in the use of insecticide-treated nets (ITNs) and long-lasting insecticidal nets (LLINs), these control measures alone may not be sufficient. IRS will be a key strategy in reaching the malaria goals set by the government of Uganda. Supplementing these control measures with education of appropriate and consistent use of ITNs and LLINs, as well as education of practicing safe living habits, such as reducing outdoor activities during peak biting hours of a mosquito, can go a long way in aiding the reduction of the burden of malaria in Uganda.

A Regional Model for Malaria Vector Developmental Habitats Evaluated Using Explicit, Pond-Resolving Surface Hydrology Simulations

Dynamical malaria models can relate precipitation to the availability of vector breeding sites using simple models of surface hydrology. Here, a revised scheme is developed for the VECTRI malaria model, which is evaluated alongside the default scheme using a two year simulation by HYDREMATS, a 10 metre resolution, village-scale model that explicitly simulates individual ponds. Despite the simplicity of the two VECTRI surface hydrology parametrization schemes, they can reproduce the sub-seasonal evolution of fractional water coverage. Calibration of the model parameters is required to simulate the mean pond fraction correctly. The default VECTRI model tended to overestimate water fraction in periods subject to light rainfall events and underestimate it during periods of intense rainfall. This systematic error was improved in the revised scheme by including the a parametrization for surface run-off, such that light rainfall below the initial abstraction threshold does not contribute to ponds. After calibration of the pond model, the VECTRI model was able to simulate vector densities that compared well to the detailed agent based model contained in HYDREMATS without further parameter adjustment. Substituting local rain-gauge data with satellite-retrieved precipitation gave a reasonable approximation, raising the prospects for regional malaria simulations even in data sparse regions. However, further improvements could be made if a method can be derived to calibrate the key hydrology parameters of the pond model in each grid cell location, possibly also incorporating slope and soil texture.

Novel mutations in K13 propeller gene of artemisinin-resistant Plasmodium falciparum

We looked for mutations in the Plasmodium falciparum K13 propeller gene of an artemisinin-resistant parasite on islands in Lake Victoria, Kenya, where transmission in 2012–2013 was high. The 4 new types of nonsynonymous, and 5 of synonymous, mutations we detected among 539 samples analyzed provide clues to understanding artemisinin-resistant parasites.

Unraveling Host-Vector-Arbovirus Interactions by Two-Gene High Resolution Melting Mosquito Bloodmeal Analysis in a Kenyan Wildlife-Livestock Interface

The blood-feeding patterns of mosquitoes are directly linked to the spread of pathogens that they transmit. Efficient identification of arthropod vector bloodmeal hosts can identify the diversity of vertebrate species potentially involved in disease transmission cycles. While molecular bloodmeal analyses rely on sequencing of cytochrome b (cyt b) or cytochrome oxidase 1 gene PCR products, recently developed bloodmeal host identification based on high resolution melting (HRM) analyses of cyt b PCR products is more cost-effective. To resolve the diverse vertebrate hosts that mosquitoes may potentially feed on in sub-Saharan Africa, we utilized HRM profiles of both cyt b and 16S ribosomal RNA genes. Among 445 blood-fed Aedeomyia, Aedes, Anopheles, Culex, Mansonia, and Mimomyia mosquitoes from Kenya’s Lake Victoria and Lake Baringo regions where many mosquito-transmitted pathogens are endemic, we identified 33 bloodmeal hosts including humans, eight domestic animal species, six peridomestic animal species and 18 wildlife species. This resolution of vertebrate host species was only possible by comparing profiles of both cyt b and 16S markers, as melting profiles of some pairs of species were similar for either marker but not both. We identified mixed bloodmeals in a Culex pipiens from Mbita that had fed on a goat and a human and in two Mansonia africana mosquitoes from Baringo that each had fed on a rodent (Arvicanthis niloticus) in addition to a human or baboon. We further detected Sindbis and Bunyamwera viruses in blood-fed mosquito homogenates by Vero cell culture and RT-PCR in Culex, Aedeomyia, Anopheles and Mansonia mosquitoes from Baringo that had fed on humans and livestock. The observed mosquito feeding on both arbovirus amplifying hosts (including sheep and goats) and possible arbovirus reservoirs (birds, porcupine, baboons, rodents) informs arbovirus disease epidemiology and vector control strategies.

Parasites and vectors of malaria on Rusinga Island, Western Kenya

Background

There is a dearth of information on malaria endemicity in the islands of Lake Victoria in western Kenya. In this study malaria prevalence and Plasmodium sporozoite rates on Rusinga Island were investigated. The contribution of different Anopheles species to indoor and outdoor transmission of malaria was also determined.

Methods

Active case detection through microscopy was used to diagnose malaria in a 10% random sample of the human population on Rusinga Island and a longitudinal entomological survey conducted in Gunda village in 2012. Nocturnally active host-seeking mosquitoes were captured indoors and outdoors using odour-baited traps. Anopheles species were tested for the presence of Plasmodium parasites using an enzyme linked immunosorbent assay. All data were analyzed using generalized linear models.

Results

Single infections of Plasmodium falciparum (88.1%), P. malariae (3.96%) and P. ovale (0.79%) as well as multiple infections (7.14%) of these parasites were found on Rusinga Island. The overall malaria prevalence was 10.9%. The risk of contracting malaria was higher among dwellers of Rusinga West than Rusinga East locations (Odds Ratio [OR] = 1.5, 95% Confidence Interval [CI] 1.14 – 1.97, P = 0.003). Parasite positivity was significantly associated with individuals who did not use malaria protective measures (OR = 2.65, 95% CI 1.76 – 3.91, p < 0.001). A total of 1,684 mosquitoes, including 74 anophelines, were captured. Unlike Culex species, more of which were collected indoors than outdoors (P < 0.001), the females of An. gambiae s.l. (P = 0.477), An. funestus s.l. (P = 0.153) and Mansonia species captured indoors versus outdoors were not different. The 46 An. gambiae s.l. collected were mainly An. arabiensis (92.3%). Of the 62 malaria mosquitoes tested, 4, including 2 indoor and 2 outdoor-collected individuals had Plasmodium.

Conclusion

The rather significant and unexpected contribution of P. malariae and P. ovale to the overall malaria prevalence on Rusinga Island underscores the epidemiological importance of these species in the big push towards eliminating malaria. Although current entomological interventions mainly target indoor environments, additional strategies should be considered to prevent outdoor transmission of malaria.

Low parasitemia in submicroscopic infections significantly impacts malaria diagnostic sensitivity in the highlands of Western Kenya

Asymptomatic malaria infections represent a major challenge in malaria control and elimination in Africa. They are reservoirs of malaria parasite that can contribute to disease transmission. Therefore, identification and control of asymptomatic infections are important to make malaria elimination feasible. In this study, we investigated the extent and distribution of asymptomatic malaria in Western Kenya and examined how varying parasitemia affects performance of diagnostic methods including microscopy, conventional PCR, and quantitative PCR. In addition, we compared parasite prevalence rates and parasitemia levels with respect to topography and age in order to explore factors that influence malaria infection. Over 11,000 asymptomatic blood samples from children and adolescents up to 18 years old representing broad areas of Western Kenya were included. Quantitative PCR revealed the highest parasite positive rate among all methods and malaria prevalence in western Kenya varied widely from less than 1% to over 50%. A significantly lower parasitemia was detected in highland than in lowland samples and this contrast was also observed primarily among submicroscopic samples. Although we found no correlation between parasitemia level and age, individuals of younger age group (aged <14) showed significantly higher parasite prevalence. In the lowlands, individuals of aged 5–14 showed significantly higher prevalence than those under age 5. Our findings highlight the need for a more sensitive and time-efficient assay for asymptomatic malaria detection particularly in areas of low-transmission. Combining QPCR with microscopy can enhance the capacity of detecting submicroscopic asymptomatic malaria infections.