James Kongere

Impacts of insecticide treated bed nets on Anopheles gambiae s.l. populations in Mbita district and Suba district, Western Kenya

BackgroundAbundance and species composition of sympatric malaria vector species are the important factors governing transmission intensity. A widespread insecticidal bed net coverage may replace endophagic species with exophagic species. However, unique local environments also influence a vector population. This study examined the impacts of insecticidal bed nets on An. gambiae s.l populations in Mbita District and Suba District.MethodsThe species compositions of An. gambiae s.l. larvae were compared between 1997, 2009 and 2010 and between geographical areas. The abundance and species composition of An. gambiae s.l. females resting indoors were compared between 1999, 2008 and 2010 and between geographical areas. Bed net coverage was also examined temporally and spatially, and its relationships with vector abundance and species composition were examined.ResultsThe relative abundance of An. gambiae s.s. larvae was 31.4% in 1997, decreasing to 7.5% in 2008 and 0.3% in 2010. The density of indoor resting An. gambiae s.l. females decreased by nearly 95%, and the relative abundance of An. gambiae s.s. females decreased from 90.6% to 60.7% and 72.4% in 2008 and 2010, respectively. However, the species composition of indoor resting An. gambiae s.l. females changed little in the island villages, and An. gambiae s.s. remained dominant in the western part of the study area. The density of house resting females was negatively associated with the number of bed nets in a retrospective analysis, but the effect of bed nets on species composition was not significant in both retrospective and cross-sectional analyses.ConclusionAn increase in bed net coverage does not necessarily replace endophilic species with exophilic species. The effect of bed nets on An. gambiae s.l. populations varies spatially, and locally unique environments are likely to influence the species composition.

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.

Sleeping on the floor decreases insecticide treated bed net use and increases risk of malaria in children under 5 years of age in Mbita District, Kenya

Children who sleep on the floor are less likely to use long-lasting insecticidal nets (LLINs); however, the relationship between sleeping location and Plasmodium falciparum infection has not been investigated sufficiently. This study revealed whether sleeping location (bed vs floor) is associated with P. falciparum infection among children 7-59 months old. More than 60% of children slept on the floor. Younger children were significantly more likely to sleep in beds [odds ratio, OR 2.31 (95% confidence interval (CI) 2.02-2.67)]. Nearly 70% of children slept under LLINs the previous night. LLIN use among children who slept on the floor was significantly less than ones sleeping in beds [OR 0.49 (95% CI 0.35-0.68)]. The polymerase chain reaction (PCR) based P. falciparum infection rate and slide based infection rate were 65.2 and 29.7%, respectively. Both infections were significantly higher among children slept on the floor [OR1.51 (95% CI 1.08-2.10) for PCR base, OR 1.62 (95% CI 1.14-2.30) for slide base] while net availability was not significant. Sleeping location was also significant for slide based infection with fever (⩾ 37.5 °C) [2.03 (95% CI 1.14-3.84)] and high parasitemia cases (parasite ⩾ 2500 µL(-1)) [2.07 (95% CI 1.03-4.50)]. The results suggest that sleeping location has a direct bearing on the effectiveness of LLINs.

Effects of Bacillus thuringiensis israelensis on Anopheles arabiensis

Abstract Studies have shown that Culex quinquefasciatus oviposits fewer eggs in water treated with Bacillus thuringiensis var. israelensis (Bti). The present study examined the effects of Bti on adults of Anopheles arabiensis. Anopheles arabiensis oviposited in both treated and untreated water with a similar frequency. The number of eggs laid did not significantly differ between the treatments. Adult mosquitoes ingested Bti solution, but it did not significantly shorten their survival time. The neutral effects of Bti on ovipositing An. arabiensis do not reduce its effectiveness as a larvicide for malaria vector control.

Selections, frameshift mutations, and copy number variation detected on the surf 4.1 gene in the western Kenyan Plasmodium falciparum population.

BackgroundPlasmodium falciparum SURFIN4.1 is a putative ligand expressed on the merozoite and likely on the infected red blood cell, whose gene was suggested to be under directional selection in the eastern Kenyan population, but under balancing selection in the Thai population. To understand this difference, surf4.1 sequences of western Kenyan P. falciparum isolates were analysed. Frameshift mutations and copy number variation (CNV) were also examined for the parasites from western Kenya and Thailand.ResultsPositively significant departures from neutral expectations were detected on the surf4.1 region encoding C-terminus of the variable region 2 (Var2) by 3 population-based tests in the western Kenyan population as similar in the Thai population, which was not covered by the previous analysis for eastern Kenyan population. Significant excess of non-synonymous substitutions per nonsynonymous site over synonymous substitutions per synonymous site was also detected in the Var2 region. Negatively significant departures from neutral expectations was detected on the region encoding Var1 C-terminus consistent to the previous observation in the eastern Kenyan population. Parasites possessing a frameshift mutation resulting a product without intracellular Trp-rich (WR) domains were 22/23 in western Kenya and 22/36 in Thailand. More than one copy of surf4.1 gene was detected in western Kenya (4/24), but no CNV was found in Thailand (0/36).ConclusionsThe authors infer that the high polymorphism of SURFIN4.1 Var2 C-terminus in both Kenyan and Thai populations were shaped-up by diversifying selection and maintained by balancing selection. These phenomena were most likely driven by immunological pressure. Whereas the SURFIN4.1 Var1 C-terminus is suggested to be under directional selection consistent to the previous report for the eastern Kenyan population. Most western Kenyan isolates possess a frameshift mutation that would limit the expression of SURFIN4.1 on the merozoite, but only 60% of Thai isolates possess this frameshift, which would affect the level and type of the selection pressure against this protein as seen in the two extremities of Tajima’s D values for Var1 C-terminus between Kenyan and Thai populations. CNV observed in Kenyan isolates may be a consequence of this frameshift mutation to increase benefits on the merozoite surface.

Naturally acquired antibody response to Plasmodium falciparum describes heterogeneity in transmission on islands in Lake Victoria

As markers of exposure anti-malaria antibody responses can help characterise heterogeneity in malaria transmission. In the present study antibody responses to Plasmodium falciparum AMA-1, MSP-119 and CSP were measured with the aim to describe transmission patterns in meso-endemic settings in Lake Victoria. Two cross-sectional surveys were conducted in Lake Victoria in January and August 2012. The study area comprised of three settings: mainland (Ungoye), large island (Mfangano) and small islands (Takawiri, Kibuogi, Ngodhe). Individuals provided a finger-blood sample to assess malaria infection by microscopy and PCR. Antibody response to P. falciparum was determined in 4,112 individuals by ELISA using eluted dried blood from filter paper. The overall seroprevalence was 64.0% for AMA-1, 39.5% for MSP-119, and 12.9% for CSP. Between settings, seroprevalences for merozoite antigens were similar between Ungoye and Mfangano, but higher when compared to the small islands. For AMA-1, the seroconversion rates (SCRs) ranged from 0.121 (Ngodhe) to 0.202 (Ungoye), and were strongly correlated to parasite prevalence. We observed heterogeneity in serological indices across study sites in Lake Victoria. These data suggest that AMA-1 and MSP-119 sero-epidemiological analysis may provide further evidence in assessing variation in malaria exposure and evaluating malaria control efforts in high endemic area.

COMMUNITY KNOWLEDGE, ATTITUDES AND PRACTICES (KAP) DURING MDA INTEGRATED MALARIA ELIMINATION AND SCHISTOSOMIASIS AND SOIL-TRANSMITTED HELMINTHS CONTROL STUDY IN NGODHE ISLAND, LAKE VICTORIA, KENYA

Background Knowledge, attitudes and practices (KAP) of communities where mass drug administration based integrated malaria elimination and control of schistosomiasis and soil transmitted helminths (STH) is targeted will be critical in adhering to intervention strategies. KAP surveys have the potential to reveal lessons that will inform implementation in similar settings. This study sought to assess knowledge, attitudes and practices of Ngodhe islanders in Lake Victoria Kenya during mass drug administration (MDA) with artemisinin-piperaquine and low dose primaquine for malaria; albendazole for STH and praziquantel for schistosomiasis. Methods The KAP study used a pre-tested interviewer questionnaire that was administered to 239 randomly selected adults. Additionally, 4 focus group discussions (each consisting of between 8–12 participants) was done with the elders, women, youth, and mixed group. Another 6 key informant interviews were also done. Results All respondents (239) had heard about malaria and they acknowledged that it is preventable; 89.1% of respondents had heard about schistosomiasis; and another 87.4% had heard about STH. A high percentage of 96.2 had heard about the mass drug administration while 87% were aware of the integrated malaria, schistosomiasis, and STH strategy. 78.2% of participants favoured stopping MDA in case side effects were perceived to be common. Sanitation was a major challenge with only 41.3% of the respondents using latrines with the rest using bushes. Conclusions This study revealed huge awareness of the integrated strategy for malaria elimination and schistosomiasis and STH control using mass drug administration. Nonetheless, concerns on MDA drugs side effects and poor sanitation practices will require greater engagement with the community.