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Background: Significant effort and resources have been invested to control malaria transmission in sub-Saharan Africa, but it remains a major public health problem. For the parasite to be transmitted, the female Anopheles vector must survive 10-14 days following an infective bite to allow Plasmodium gametocytes to develop into infectious sporozoites. The goal of this study was to assess factors associated with wild-caught Anopheles survival and infection following host-seeking and indoor resting., Methods: The study was conducted between January 2020 to March 2022 in a longitudinal cohort of 75 households in 5 villages including a total of 755 household members in Bungoma County, Kenya. Monthly adult mosquito collection was conducted by attenuated aspiration in all enrolled households, and mosquitoes were reared for 7 days. The daily mortality rate was determined through day 7. All mosquitoes were morphologically identified. Female Anopheles were dissected, and species-level members of the Anopheles gambiae complex were resolved by molecular methods. The abdomens of all samples were processed for Plasmodium falciparum oocyst detection by PCR., Results: Within a 25-month period, the total numbers of non-Anopheles and Anopheles mosquitoes collected indoors were 12,843 and 712, respectively. Anopheles gambiae and An. funestus were the major vectors, though their distributions varied between different villages; 61.2% (n = 436/712) of the Anopheles mosquitoes survived up to day 7, with the lowest mortality rate recorded on day 5 of captivity. The survival rate also varied between the different Anopheles species. Six hundred eighty-three of 712 mosquito abdomens were tested for P. falciparum; 7.8% (53/683) tested positive for P. falciparum, with An. funestus having a higher (10%) prevalence than An. gambiae s.s. (6.0%, p = 0.095, Pearson Chi-square test). The proportion of household members sleeping under a bednet the night before mosquito collection varied across time and village. Anopheles funestus survival times were refractory to household ITN usage, and An. gambaie s.s. survival was reduced only under very high (100%) ITN usage., Conclusions: Despite ITN usage, mosquitoes still acquired blood meals and P. falciparum infections. Survival differed across species and was inversely correlated with high ITN usage in the household but not oocyst development., Competing Interests: Declarations Ethics approval and consent to participate Ethical approval was granted by Moi University Institutional Research and Ethics Committee (Formal Approval No. 0001863) and Duke University Institutional Review Board (Pro00082000). Written informed consent was obtained the household heads and participants prior to data and mosquito collection. All study methods were carried out in accordance with ethical guidelines and regulations set out by both Moi University and Duke Ethical Review Boards. Consent for publication Not applicable. Competing interests The authors declare no competing interests., (© 2024. The Author(s).)

The human infectious reservoir of Plasmodium falciparum is governed by transmission efficiency during vector-human contact and mosquito biting preferences. Understanding biting bias in a natural setting can help target interventions to interrupt transmission. In a 15-month cohort in western Kenya, we detected P. falciparum in indoor-resting Anopheles and human blood samples by qPCR and matched mosquito bloodmeals to cohort participants using short-tandem repeat genotyping. Using risk factor analyses and discrete choice models, we assessed mosquito biting behavior with respect to parasite transmission. Biting was highly unequal; 20% of people received 86% of bites. Biting rates were higher on males (biting rate ratio (BRR): 1.68; CI: 1.28-2.19), children 5-15 years (BRR: 1.49; CI: 1.13-1.98), and P. falciparum-infected individuals (BRR: 1.25; CI: 1.01-1.55). In aggregate, P. falciparum-infected school-age (5-15 years) boys accounted for 50% of bites potentially leading to onward transmission and had an entomological inoculation rate 6.4x higher than any other group. Additionally, infectious mosquitoes were nearly 3x more likely than non-infectious mosquitoes to bite P. falciparum-infected individuals (relative risk ratio 2.76, 95% CI 1.65-4.61). Thus, persistent P. falciparum transmission was characterized by disproportionate onward transmission from school-age boys and by the preference of infected mosquitoes to feed upon infected people., (© 2024. The Author(s).)

Despite concern that climate change could increase the human risk to malaria in certain areas, the temperature dependency of malaria transmission is poorly characterized. Here, we use a mechanistic model fitted to experimental data to describe how Plasmodium falciparum infection of the African malaria vector, Anopheles gambiae, is modulated by temperature, including its influences on parasite establishment, conversion efficiency through parasite developmental stages, parasite development rate, and overall vector competence. We use these data, together with estimates of the survival of infected blood-fed mosquitoes, to explore the theoretical influence of temperature on transmission in four locations in Kenya, considering recent conditions and future climate change. Results provide insights into factors limiting transmission in cooler environments and indicate that increases in malaria transmission due to climate warming in areas like the Kenyan Highlands, might be less than previously predicted., (© 2024. The Author(s).)

Background: The gold standard for diagnosing Plasmodium falciparum infection is microscopic examination of Giemsa-stained peripheral blood smears. The effectiveness of this procedure for infection surveillance and malaria control may be limited by a relatively high parasitaemia detection threshold. Persons with microscopically undetectable infections may go untreated, contributing to ongoing transmission to mosquito vectors. The purpose of this study was to determine the magnitude and determinants of undiagnosed submicroscopic P. falciparum infections in a rural area of western Kenya., Methods: A health facility-based survey was conducted, and 367 patients seeking treatment for symptoms consistent with uncomplicated malaria in Homa Bay County were enrolled. The frequency of submicroscopic P. falciparum infection was measured by comparing the prevalence of infection based on light microscopic inspection of thick blood smears versus real-time polymerase chain reaction (RT-PCR) targeting P. falciparum 18S rRNA gene. Long-lasting insecticidal net (LLIN) use, participation in nocturnal outdoor activities, and gender were considered as potential determinants of submicroscopic infections., Results: Microscopic inspection of blood smears was positive for asexual P. falciparum parasites in 14.7% (54/367) of cases. All of these samples were confirmed by RT-PCR. 35.8% (112/313) of blood smear negative cases were positive by RT-PCR, i.e., submicroscopic infection, resulting in an overall prevalence by RT-PCR alone of 45.2% compared to 14.7% for blood smear alone. Females had a higher prevalence of submicroscopic infections (35.6% or 72 out of 202 individuals, 95% CI 28.9-42.3) compared to males (24.2%, 40 of 165 individuals, 95% CI 17.6-30.8). The risk of submicroscopic infections in LLIN users was about half that of non-LLIN users (OR = 0.59). There was no difference in the prevalence of submicroscopic infections of study participants who were active in nocturnal outdoor activities versus those who were not active (OR = 0.91). Patients who participated in nocturnal outdoor activities and use LLINs while indoors had a slightly higher risk of submicroscopic infection than those who did not use LLINs (OR = 1.48)., Conclusion: Microscopic inspection of blood smears from persons with malaria symptoms for asexual stage P. falciparum should be supplemented by more sensitive diagnostic tests in order to reduce ongoing transmission of P. falciparum parasites to local mosquito vectors., (© 2021. The Author(s).)

Competing Interests: We declare no competing interests. The Barcelona Institute for Global Health (ISGlobal) is supported by the Spanish Ministry of Science and Innovation through the Centro de Excelencia Severo Ochoa 2019–2023 programme (CEX2018–000806-S), and is a member of the Catalan Program of Research Centres, Generalitat de Catalunya. The Centro de Investigação em Saúde de Manhiça (Manhiça's Health research Centre) is supported by the Government of Mozambique and the Spanish Agency for International Development.

Background: Triple antimalarial combination therapies combine potent and rapidly cleared artemisinins or related synthetic ozonides, such as arterolane, with two, more slowly eliminated partner drugs to reduce the risk of resistance. We aimed to assess the safety, tolerability, and efficacy of arterolane-piperaquine-mefloquine versus arterolane-piperaquine and artemether-lumefantrine for the treatment of uncomplicated falciparum malaria in Kenyan children., Methods: In this single-centre, open-label, randomised, non-inferiority trial done in Kilifi County Hospital, Kilifi, coastal Kenya, children with uncomplicated Plasmodium falciparum malaria were recruited. Eligible patients were aged 2-12 years and had an asexual parasitaemia of 5000-250 000 parasites per μL. The exclusion criteria included the presence of an acute illness other than malaria, the inability to tolerate oral medications, treatment with an artemisinin derivative in the previous 7 days, a known hypersensitivity or contraindication to any of the study drugs, and a QT interval corrected for heart rate (QTc interval) longer than 450 ms. Patients were randomly assigned (1:1:1), by use of blocks of six, nine, and 12, and opaque, sealed, and sequentially numbered envelopes, to receive either arterolane-piperaquine, arterolane-piperaquine-mefloquine, or artemether-lumefantrine. Laboratory staff, but not the patients, the patients' parents or caregivers, clinical or medical officers, nurses, or trial statistician, were masked to the intervention groups. For 3 days, oral artemether-lumefantrine was administered twice daily (target dose 5-24 mg/kg of bodyweight of artemether and 29-144 mg/kg of bodyweight of lumefantrine), and oral arterolane-piperaquine (arterolane dose 4 mg/kg of bodyweight; piperaquine dose 20 mg/kg of bodyweight) and oral arterolane-piperaquine-mefloquine (mefloquine dose 8 mg/kg of bodyweight) were administered once daily. All patients received 0·25 mg/kg of bodyweight of oral primaquine at hour 24. All patients were admitted to Kilifi County Hospital for at least 3 consecutive days and followed up at day 7 and, thereafter, weekly for up to 42 days. The primary endpoint was 42-day PCR-corrected efficacy, defined as the absence of treatment failure in the first 42 days post-treatment, of arterolane-piperaquine-mefloquine versus artemether-lumefantrine, and, along with safety, was analysed in the intention-to-treat population, which comprised all patients who received at least one dose of a study drug. The 42-day PCR-corrected efficacy of arterolane-piperaquine-mefloquine versus arterolane-piperaquine was an important secondary endpoint and was also analysed in the intention-to-treat population. The non-inferiority margin for the risk difference between treatments was -7%. The study is registered in ClinicalTrials.gov, NCT03452475, and is completed., Findings: Between March 7, 2018, and May 2, 2019, 533 children with P falciparum were screened, of whom 217 were randomly assigned to receive either arterolane-piperaquine (n=73), arterolane-piperaquine-mefloquine (n=72), or artemether-lumefantrine (n=72) and comprised the intention-to-treat population. The 42-day PCR-corrected efficacy after treatment with arterolane-piperaquine-mefloquine (100%, 95% CI 95-100; 72/72) was non-inferior to that after treatment with artemether-lumefantrine (96%, 95% CI 88-99; 69/72; risk difference 4%, 95% CI 0-9; p=0·25). The 42-day PCR-corrected efficacy of arterolane-piperaquine-mefloquine was non-inferior to that of arterolane-piperaquine (100%, 95% CI 95-100; 73/73; risk difference 0%). Vomiting rates in the first hour post-drug administration were significantly higher in patients treated with arterolane-piperaquine (5%, 95% CI 2-9; ten of 203 drug administrations; p=0·0013) or arterolane-piperaquine-mefloquine (5%, 3-9; 11 of 209 drug administrations; p=0·0006) than in patients treated with artemether-lumefantrine (1%, 0-2; three of 415 drug administrations). Upper respiratory tract complaints (n=26 for artemether-lumefantrine; n=19 for arterolane-piperaquine-mefloquine; n=23 for arterolane-piperaquine), headache (n=13; n=4; n=5), and abdominal pain (n=7; n=5; n=5) were the most frequently reported adverse events. There were no deaths., Interpretation: This study shows that arterolane-piperaquine-mefloquine is an efficacious and safe treatment for uncomplicated falciparum malaria in children and could potentially be used to prevent or delay the emergence of antimalarial resistance., Funding: UK Department for International Development, The Wellcome Trust, The Bill & Melinda Gates Foundation, Sun Pharmaceutical Industries., Competing Interests: Declaration of interests We declare no competing interests., (Copyright © 2021 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 license. Published by Elsevier Ltd.. All rights reserved.)

Background: Asymptomatic Plasmodium falciparum infections are common in sub-Saharan Africa, but their effect on subsequent symptomaticity is incompletely understood., Methods: In a 29-month cohort of 268 people in Western Kenya, we investigated the association between asymptomatic P. falciparum and subsequent symptomatic malaria with frailty Cox models., Results: Compared to being uninfected, asymptomatic infections were associated with an increased 1 month likelihood of symptomatic malaria (adjusted hazard ratio [aHR]: 2.61, 95% CI: 2.05 to 3.33), and this association was modified by sex, with females (aHR: 3.71, 95% CI: 2.62 to 5.24) at higher risk for symptomaticity than males (aHR: 1.76, 95% CI: 1.24 to 2.50). This increased symptomatic malaria risk was observed for asymptomatic infections of all densities and in people of all ages. Long-term risk was attenuated but still present in children under age 5 (29-month aHR: 1.38, 95% CI: 1.05 to 1.81)., Conclusions: In this high-transmission setting, asymptomatic P. falciparum can be quickly followed by symptoms and may be targeted to reduce the incidence of symptomatic illness., Funding: This work was supported by the National Institute of Allergy and Infectious Diseases (R21AI126024 to WPO, R01AI146849 to WPO and SMT)., Competing Interests: KS, JM, AO, EF, LA, SM, JE, BP, WP, ST No competing interests declared, (© 2021, Sumner et al.)

Background: The lack of background disease incidence rates in sub-Saharan countries where the RTS,S/AS01 E malaria vaccine is being implemented may hamper the assessment of vaccine safety and effectiveness. This study aimed to document baseline incidence rates of meningitis, malaria, mortality, and other health outcomes prior to vaccine introduction through the Malaria Vaccine Implementation Programme., Methods: An ongoing disease surveillance study is combining prospective cohort event monitoring and hospital-based disease surveillance in three study sites in Ghana and Kenya. An interim analysis was performed on the prospective cohort in which children were enrolled in two age-groups (the 5 to 17 months or 6 to 12 weeks age-group), capturing data in the framework of routine medical practice before the introduction of the malaria vaccine. Incidence and mortality rates were computed with 95% confidential intervals (CI) using an exact method for a Poisson variable., Results: This analysis includes 14,329 children; 7248 (50.6%) in the 6 to 12 weeks age-group and 7081 (49.4%) in the 5 to 17 months age-group. In the 5 to 17 months age-group (where the malaria vaccine was planned to be subsequently rolled out) the meningitis, malaria, severe malaria and cerebral malaria incidences were 92 (95% CI 25-236), 47,824 (95% CI 45,411-50,333), 1919 (95% CI 1461-2476) and 33 (95% CI 1-181) per 100,000 person-years, respectively. The all-cause mortality was 969 (95% CI 699-1310) per 100,000 person-years., Conclusion: Incidence estimates of multiple health outcomes are being generated to allow before-after vaccine introduction comparisons that will further characterize the benefit-risk profile of the RTS,S/AS01 E vaccine., Trial Registration: clinicaltrials.gov NCT02374450.

Background: Interferon (IFN)- λ4, a type III IFN, production is controlled by a dinucleotide frameshift variant (rs368234815-dG/TT) within the first exon of the IFNL4 gene. Carriers of the IFNL4-dG allele but not the IFNL4-TT allele are able to produce the IFN-λ4 protein. Patients with hepatitis C virus that do not produce the IFN-λ4 protein have higher rates of viral clearance suggesting a potential inhibitory role of IFN-λ4 in liver-tropic infections., Methods: In this study, it was investigated whether children infected with Plasmodium falciparum, which has a well-characterized liver stage infection, would be more susceptible to clinical malaria relative to their IFNL4-rs368234815 allele. A cohort of 122 children from a malaria holoendemic region of Kenya was analysed. Episodes of clinical malaria and upper respiratory tract infections (URTIs) were determined using information collected from birth to 2 years of age. The dinucleotide frameshift variant IFNL4-rs368234815-dG/TT was genotyped using a TaqMan assay., Results: In this cohort, 33% of the study participants had the dG/dG genotype, 45% had the dG/TT genotype, and 22% had TT/TT genotype. The number and time to first episode of clinical malaria and URTIs with respect to the IFNL4-rs368234815 allele was evaluated. It was found that children that carried the IFNL4-rs368234815-dG allele had an increased number of clinical malaria episodes. In addition, there was a significant association between earlier age of first malaria infection with carriers of the IFNL4-dG allele (p-value: 0.021)., Conclusion: The results suggest that the ability to produce IFN-λ4 negatively affects host immune protection against P. falciparum malaria in Kenyan children.

Background: Transmission stemming from asymptomatic infections is increasingly being recognized as a threat to malaria elimination. In many regions, malaria transmission is seasonal. It is not well understood whether Plasmodium falciparum modulates its investment in transmission to coincide with seasonal vector abundance., Methods: We sampled 1116 asymptomatic individuals in the wet season, when vectors are abundant, and 1743 in the dry season, in two sites in western Kenya, representing different transmission intensities (Chulaimbo, moderate transmission, and Homa Bay, low transmission). Blood samples were screened for P. falciparum by qPCR, and gametocytes by pfs25 RT-qPCR., Results: Parasite prevalence by qPCR was 27.1% (Chulaimbo, dry), 48.2% (Chulaimbo, wet), 9.4% (Homabay, dry), and 7.8% (Homabay, wet). Mean parasite densities did not differ between seasons (P = 0.562). pfs25 transcripts were detected in 119/456 (26.1%) of infections. In the wet season, fewer infections harbored detectable gametocytes (22.3% vs. 33.8%, P = 0.009), but densities were 3-fold higher (wet: 3.46 transcripts/uL, dry: 1.05 transcripts/uL, P < 0.001). In the dry season, 4.0% of infections carried gametocytes at moderate-to-high densities likely infective (> 1 gametocyte per 2 uL blood), compared to 7.9% in the wet season. Children aged 5-15 years harbored 76.7% of infections with gametocytes at moderate-to-high densities., Conclusions: Parasites increase their investment in transmission in the wet season, reflected by higher gametocyte densities. Despite increased gametocyte densities, parasite density remained similar across seasons and were often below the limit of detection of microscopy or rapid diagnostic test, thus a large proportion of infective infections would escape population screening in the wet season. Seasonal changes of gametocytemia in asymptomatic infections need to be considered when designing malaria control measures.

Background: Prevalence of Prevalence of malaria in pregnancy (MiP) in Kenya ranges from 9% to 18%. We estimated the prevalence and factors associated with MiP and anemia in pregnancy (AiP) among asymptomatic women attending antenatal care (ANC) visits., Methods: We performed a cross-sectional study among pregnant women attending ANC at Msambweni Hospital, between September 2018 and February 2019. Data was collected and analyzed in Epi Info 7. Descriptive statistics were calculated and we compared MiP and AiP in asymptomatic cases to those without either condition. Adjusted prevalence Odds odds ratios (aPOR) and 95% confidence intervals (CI) were calculated to identify factors associated with asymptomatic MiP and AiP., Results: We interviewed 308 study participants; their mean age was 26.6 years (± 5.8 years), mean gestational age was 21.8 weeks (± 6.0 weeks), 173 (56.2%) were in the second trimester of pregnancy, 12.9% (40/308) had MiP and 62.7% had AiP. Women who were aged ≤ 20 years had three times likelihood of developing MiP (aPOR = 3.1 Cl: 1.3-7.35) compared to those aged >20 years old. The likelihood of AiP was higher among women with gestational age ≥ 16 weeks (aPOR = 3.9, CI: 1.96-7.75), those with parasitemia (aPOR = 3.3, 95% CI: 1.31-8.18), those in third trimester of pregnancy (aPOR = 2.6, 95% CI:1.40-4.96) and those who reported eating soil as a craving during pregnancy (aPOR = 1.9, 95%CI:1.15-3.29)., Conclusions: Majority of the women had asymptomatic MiP and AiP. MiP was observed in one tenth of all study participants. Asymptomatic MiP was associated with younger age while AiP was associated with gestational age parasitemia, and soil consumption as a craving during pregnancy., Competing Interests: The authors have declared that no competing interests exist.

Background: Endemic Burkitt lymphoma (eBL) is an aggressive B cell non-Hodgkin lymphoma associated with antigenic stimulation from Plasmodium falciparum malaria. Whether eBL risk is related to malaria parasite density is unknown. To address this issue, children with eBL, asymptomatic and clinical malaria, as a surrogate of malaria parasite density, were assessed., Methods: Malaria-related laboratory results (parasite density, haemoglobin, platelet count, and white cell count [WBC]) count) were compiled for 4019 eBL cases and 80,532 subjects evaluated for asymptomatic malaria or clinical malaria (severe malaria anaemia, hyperparasitaemia, cerebral malaria, malaria prostration, moderate malaria, and mild malaria) in 21 representative studies published in Africa (mostly East Africa) and 850 eBL cases and 2878 controls with primary data from the Epidemiology of Burkitt Lymphoma in East African Children and Minors (EMBLEM) case-control study in Uganda, Tanzania, and Kenya. The average values of malaria-related laboratory results were computed by condition and trends across single-year age groups were assessed using regression and spline models., Results: Overall, malaria infection or malaria was diagnosed in 37,089 of children compiled from the literature. Children with eBL and asymptomatic parasitaemia/antigenaemia, but not those with clinical malaria, were closest in their mean age (age 7.1-7.2 vs. 7.4-9.8 years), haemoglobin level (10.0-10.4 vs. 11.7-12.3 g/dL), malaria parasite density (2800 vs. 1827-7780 parasites/µL), platelet count (347,000-353,000 vs. 244,000-306,000 platelets/µL), and WBC count (8180-8890 vs. 7100-7410 cells/µL). Parasite density in these two groups peaked between four to five years, then decreased steadily thereafter; conversely, haemoglobin showed a corresponding increase with age. Children with clinical malaria were markedly different: all had an average age below 5 years, had dramatically elevated parasite density (13,905-869,000 parasites/µL) and dramatically decreased platelet count (< 159,000 platelets/µL) and haemoglobin (< 7 g/dL)., Conclusions: eBL and asymptomatic parasitaemia/antigenaemia, but not clinical malaria, were the most similar conditions with respect to mean age and malaria-related laboratory results. These results suggest that children with asymptomatic parasitaemia/antigenaemia may be the population at risk of eBL.

A possible malaria control approach involves the dissemination in mosquitoes of inherited symbiotic microbes to block Plasmodium transmission. However, in the Anopheles gambiae complex, the primary African vectors of malaria, there are limited reports of inherited symbionts that impair transmission. We show that a vertically transmitted microsporidian symbiont (Microsporidia MB) in the An. gambiae complex can impair Plasmodium transmission. Microsporidia MB is present at moderate prevalence in geographically dispersed populations of An. arabiensis in Kenya, localized to the mosquito midgut and ovaries, and is not associated with significant reductions in adult host fecundity or survival. Field-collected Microsporidia MB infected An. arabiensis tested negative for P. falciparum gametocytes and, on experimental infection with P. falciparum, sporozoites aren't detected in Microsporidia MB infected mosquitoes. As a microbe that impairs Plasmodium transmission that is non-virulent and vertically transmitted, Microsporidia MB could be investigated as a strategy to limit malaria transmission.

Novel interventions that leverage the heterogeneity of parasite transmission are needed to achieve malaria elimination. To better understand spatial and temporal dynamics of transmission, we applied amplicon next-generation sequencing of two polymorphic gene regions (csp and ama1) to a cohort identified via reactive case detection in a high-transmission setting in western Kenya. From April 2013 to July 2014, we enrolled 442 symptomatic children with malaria, 442 matched controls, and all household members of both groups. Here, we evaluate genetic similarity between infected individuals using three indices: sharing of parasite haplotypes on binary and proportional scales and the L1 norm. Symptomatic children more commonly share haplotypes with their own household members. Furthermore, we observe robust temporal structuring of parasite genetic similarity and identify the unique molecular signature of an outbreak. These findings of both micro- and macro-scale organization of parasite populations might be harnessed to inform next-generation malaria control measures.

Background: In Kenya, malaria remains a major public health menace equally affecting the semi-arid to arid ecologies. However, entomologic knowledge of malaria vectors in such areas remains poor., Methods: Morphologically-identified wild-caught Anopheles funestus (s.l.) specimens trapped outdoors from the semi-arid to arid area of Kacheliba, West Pokot County, Kenya, were analysed by PCR and sequencing for species identification, malaria parasite infection and host blood-meal sources., Results: Three hundred and thirty specimens were analysed to identify sibling species of the An. funestus group, none of which amplified using the available primers; two were infected with Plasmodium falciparum and Plasmodium ovale, separately, while 84% (n = 25) of the blood-fed specimens had fed on humans. Mitochondrial cytochrome c oxidase subunit 1 (cox1) and nuclear ribosomal internal transcribed spacer 2 (ITS2) sequences of 55 specimens (Plasmodium-positive, blood-fed and Plasmodium-negative) did not match reference sequences, possibly suggesting a previously unreported species, resolving as two clades., Conclusions: Our findings indicate the existence of yet-to-be identified and described anopheline species with a potential as malaria vectors in Kenya.

Background: Parasite genetic diversity and multiplicity of infection (MOI) affect clinical outcomes, response to drug treatment and naturally-acquired or vaccine-induced immunity. Traditional methods often underestimate the frequency and diversity of multiclonal infections due to technical sensitivity and specificity. Next-generation sequencing techniques provide a novel opportunity to study complexity of parasite populations and molecular epidemiology., Methods: Symptomatic and asymptomatic Plasmodium vivax samples were collected from health centres/hospitals and schools, respectively, from 2011 to 2015 in Ethiopia. Similarly, both symptomatic and asymptomatic Plasmodium falciparum samples were collected, respectively, from hospitals and schools in 2005 and 2015 in Kenya. Finger-pricked blood samples were collected and dried on filter paper. Long amplicon (> 400 bp) deep sequencing of merozoite surface protein 1 (msp1) gene was conducted to determine multiplicity and molecular epidemiology of P. vivax and P. falciparum infections. The results were compared with those based on short amplicon (117 bp) deep sequencing., Results: A total of 139 P. vivax and 222 P. falciparum samples were pyro-sequenced for pvmsp1 and pfmsp1, yielding a total of 21 P. vivax and 99 P. falciparum predominant haplotypes. The average MOI for P. vivax and P. falciparum were 2.16 and 2.68, respectively, which were significantly higher than that of microsatellite markers and short amplicon (117 bp) deep sequencing. Multiclonal infections were detected in 62.2% of the samples for P. vivax and 74.8% of the samples for P. falciparum. Four out of the five subjects with recurrent P. vivax malaria were found to be a relapse 44-65 days after clearance of parasites. No difference was observed in MOI among P. vivax patients of different symptoms, ages and genders. Similar patterns were also observed in P. falciparum except for one study site in Kenyan lowland areas with significantly higher MOI., Conclusions: The study used a novel method to evaluate Plasmodium MOI and molecular epidemiological patterns by long amplicon ultra-deep sequencing. The complexity of infections were similar among age groups, symptoms, genders, transmission settings (spatial heterogeneity), as well as over years (pre- vs. post-scale-up interventions). This study demonstrated that long amplicon deep sequencing is a useful tool to investigate multiplicity and molecular epidemiology of Plasmodium parasite infections.

Malaria is a worldwide health problem that affects two-thirds of the world population. Plasmodium invasion of anopheline mosquitoes is an obligatory step for malaria transmission. However, mosquito-malaria molecular interactions in nature are not clear. A genetic variation within mosquito fibrinogen related-protein 30 (FBN30) was previously identified to be associated with Plasmodium falciparum infection in natural Anopheles gambiae populations at malaria endemic areas in Kenya, and reducing FBN30 expression by RNAi makes mosquitoes more susceptible to P. berghei. New results show that FBN30 is a secreted octamer that binds to both P. berghei and clinically circulating P. falciparum from malaria endemic areas in Kenya, but not laboratory P. falciparum strain NF54. Moreover, the natural genetic mutation (T to C) within FBN30 signal peptide, which changes the position 10 amino acid from phenylalanine to leucine, reduces protein expression by approximately half. This change is consistent to more susceptible An. gambiae to P. falciparum infection in the field. FBN30 in natural An. gambiae is proposed to work as a pathogen recognition molecule in inhibiting P. falciparum transmission in malaria endemic areas.

Severe malaria (SM) is a life-threatening complication of infection with Plasmodium falciparum Epidemiological observations have long indicated that immunity against SM is acquired relatively rapidly, but prospective studies to investigate its immunological basis are logistically challenging and have rarely been undertaken. We investigated the merozoite targets and antibody-mediated mechanisms associated with protection against SM in Kenyan children aged 0 to 2 years. We designed a unique prospective matched case-control study of well-characterized SM clinical phenotypes nested within a longitudinal birth cohort of children (n= 5,949) monitored over the first 2 years of life. We quantified immunological parameters in sera collected before the SM event in cases and their individually matched controls to evaluate the prospective odds of developing SM in the first 2 years of life. Anti-AMA1 antibodies were associated with a significant reduction in the odds of developing SM (odds ratio [OR] = 0.37; 95% confidence interval [CI] = 0.15 to 0.90; P= 0.029) after adjustment for responses to all other merozoite antigens tested, while those against MSP-2, MSP-3, Plasmodium falciparum Rh2 [PfRh2], MSP-119, and the infected red blood cell surface antigens were not. The combined ability of total IgG to inhibit parasite growth and mediate the release of reactive oxygen species from neutrophils was associated with a marked reduction in the odds of developing SM (OR = 0.07; 95% CI = 0.006 to 0.82;P= 0.03). Assays of these two functional mechanisms were poorly correlated (Spearman rank correlation coefficient [rs] = 0.12;P= 0.07). Our data provide epidemiological evidence that multiple antibody-dependent mechanisms contribute to protective immunity via distinct targets whose identification could accelerate the development of vaccines to protect against SM., (Copyright © 2016 Murungi et al.)

Background: Insecticide treated nets (ITNs) and indoor residual spraying (IRS) have been scaled up for malaria prevention in sub-Saharan Africa. However, there are few studies on the benefit of implementing IRS in areas with moderate to high coverage of ITNs. We evaluated the impact of an IRS program on malaria related outcomes in western Kenya, an area of intense perennial malaria transmission and moderate ITN coverage (55-65% use of any net the previous night)., Methods: The Kenya Division of Malaria Control, with support from the US President's Malaria Initiative, conducted IRS in one lowland endemic district with moderate coverage of ITNs. Surveys were conducted in the IRS district and a neighboring district before IRS, after one round of IRS in July-Sept 2008 and after a second round of IRS in April-May 2009. IRS was conducted with pyrethroid insecticides. At each survey, 30 clusters were selected for sampling and within each cluster, 12 compounds were randomly selected. The primary outcomes measured in all residents of selected compounds included malaria parasitemia, clinical malaria (P. falciparum infection plus history of fever) and anemia (Hb<8) of all residents in randomly selected compounds. At each survey round, individuals from the IRS district were matched to those from the non-IRS district using propensity scores and multivariate logistic regression models were constructed based on the matched dataset., Results: At baseline and after one round of IRS, there were no differences between the two districts in the prevalence of malaria parasitemia, clinical malaria or anemia. After two rounds of IRS, the prevalence of malaria parasitemia was 6.4% in the IRS district compared to 16.7% in the comparison district (OR = 0.36, 95% CI = 0.22-0.59, p<0.001). The prevalence of clinical malaria was also lower in the IRS district (1.8% vs. 4.9%, OR = 0.37, 95% CI = 0.20-0.68, p = 0.001). The prevalence of anemia was lower in the IRS district but only in children under 5 years of age (2.8% vs. 9.3%, OR = 0.30, 95% CI = 0.13-0.71, p = 0.006). Multivariate models incorporating both IRS and ITNs indicated that both had an impact on malaria parasitemia and clinical malaria but the independent effect of ITNs was reduced in the district that had received two rounds of IRS. There was no statistically significant independent effect of ITNs on the prevalence of anemia in any age group., Conclusions: Both IRS and ITNs are effective tools for reducing malaria burden and when implemented in an area of moderate to high transmission with moderate ITN coverage, there may be an added benefit of IRS. The value of adding ITNs to IRS is less clear as their benefits may be masked by IRS. Additional monitoring of malaria control programs that implement ITNs and IRS concurrently is encouraged to better understand how to maximize the benefits of both interventions, particularly in the context of increasing pyrethroid resistance.

Recent studies of Plasmodium berghei malaria in mice show that high blood-stage parasitemia levels inhibit the development of subsequent liver-stage infections. Whether a similar inhibitory effect on liver-stage Plasmodium falciparum by blood-stage infection occurs in humans is unknown. We have analyzed data from a treatment-time-to-infection cohort of children < 10 years of age residing in a malaria holoendemic area of Kenya where people experience a new blood-stage infection approximately every 2 weeks. We hypothesized that if high parasitemia blocked the liver stage, then high levels of parasitemia should be followed by a "skipped" peak of parasitemia. Statistical analysis of "natural infection" field data and stochastic simulation of infection dynamics show that the data are consistent with high P. falciparum parasitemia inhibiting liver-stage parasite development in humans.

Long-term success of ongoing malaria control efforts based on mosquito bed nets (long-lasting insecticidal net) and indoor residual spraying is dependent on continuous monitoring of mosquito vectors, and thus on effective mosquito sampling tools. The objective of our study was to identify the most efficient mosquito sampling tool(s) for routine vector surveillance for malaria and lymphatic filariasis transmission in coastal Kenya. We evaluated relative efficacy of five collection methods--light traps associated with a person sleeping under a net, pyrethrum spray catches, Prokopack aspirator, clay pots, and urine-baited traps--in four villages representing three ecological settings along the south coast of Kenya. Of the five methods, light traps were the most efficient for collecting female Anopheles gambiae s.l. (Giles) (Diptera: Culicidae) and Anopheles funestus (Giles) (Diptera: Culicidae) mosquitoes, whereas the Prokopack aspirator was most efficient in collecting Culex quinquefasciatus (Say) (Diptera: Culicidae) and other culicines. With the low vector densities here, and across much of sub-Saharan Africa, wherever malaria interventions, long-lasting insecticidal nets, and/or indoor residual spraying are in place, the use of a single mosquito collection method will not be sufficient to achieve a representative sample of mosquito population structure. Light traps will remain a relevant tool for host-seeking mosquitoes, especially in the absence of human landing catches. For a fair representation of the indoor mosquito population, light traps will have to be supplemented with aspirator use, which has potential for routine monitoring of indoor resting mosquitoes, and can substitute the more labor-intensive and intrusive pyrethrum spray catches. There are still no sufficiently efficient mosquito collection methods for sampling outdoor mosquitoes, particularly those that are bloodfed.

Malaria-infected individuals can develop antibodies which reduce the infectiousness of Plasmodium gametocytes to biting Anopheles mosquitoes. When ingested in a bloodmeal together with gametocytes, these antibodies reduce or prevent subsequent parasite maturation in the insect host. This transmission-blocking immunity is usually measured in human sera by testing its effect on the infectivity of gametocytes grown in vitro. Here we evaluate evidence of transmission-blocking immunity in eight studies conducted in three African countries. Plasmodium falciparum gametocytes isolated from each individual were fed to mosquitoes in both autologous plasma collected with the parasites, and permissive serum from non-exposed donors. Evidence of transmission reducing effects of autologous plasma was found in all countries. Experiments involving 116 Gambian children (aged 0.5-15 years) were combined to determine which factors were associated with transmission reducing immune responses. The chances of infecting at least one mosquito and the average proportion of infected mosquitoes were negatively associated with recent exposure to gametocytes and sampling late in the season. These results suggest that effective malaria transmission-reducing antibodies do not commonly circulate in African children, and that recent gametocyte carriage is required to initiate and/or boost such responses., (Copyright © 2010 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.)

Anopheles arabiensis is a major vector of Plasmodium falciparum in southern Zambia. This study aimed to determine the rate of multiple human blood meals taken by An. arabiensis to more accurately estimate entomologic inoculation rates (EIRs). Mosquitoes were collected in four village areas over two seasons. DNA from human blood meals was extracted and amplified at four microsatellite loci. Using the three-allele method, which counts > or = 3 alleles at any microsatellite locus as a multiple blood meal, we determined that the overall frequency of multiple blood meals was 18.9%, which was higher than rates reported for An. gambiae in Kenya and An. funestus in Tanzania. Computer simulations showed that the three-allele method underestimates the true multiple blood meal proportion by 3-5%. Although P. falciparum infection status was not shown to influence the frequency of multiple blood feeding, the high multiple feeding rate found in this study increased predicted malaria risk by increasing EIR.

Severe malarial anemia (SMA) is a leading cause of mortality among children in sub-Saharan Africa. Although the novel cytokine, interleukin (IL)-23, promotes anemia in chronic inflammatory diseases, the role of IL-23 in SMA remains undefined. Since IL-23 and IL-12 share the IL-12p40 subunit and IL-12Rbeta1 receptor, and are down-regulated by IL-10, relationships among these cytokines were explored in Kenyan children with varying severities of malarial anemia. Children with malarial anemia had increased circulating IL-23 and IL-10 and decreased IL-12 relative to healthy controls. Enhanced anemia severity and elevated parasitemia were associated with increased IL-10 relative to IL-23 and IL-12. Further exploration of the relationships among the cytokines using an in vitro model in which peripheral blood mononuclear cells were treated with synthetic hemozoin (sHz, malarial pigment) revealed that IL-12p35 and IL-23p19 transcripts had a sustained induction over 72 h, while IL-12p40 and IL-10 message peaked at 24 h, and rapidly declined thereafter. Taken together, results here show that IL-23 is elevated in children with malarial anemia, and that IL-10 and IL-12 appear to have important regulatory effects on IL-23 production during childhood malaria.

The invasion of erythrocytes by Plasmodium falciparum occurs through multiple pathways that can be studied in vitro by examining the invasion of erythrocytes treated with enzymes such as neuraminidase, trypsin, and chymotrypsin. We have studied the invasion pathways used by 31 Kenyan P. falciparum isolates from children with uncomplicated or severe malaria. Six distinct invasion profiles were detected, out of eight possible profiles. The majority of isolates (23 of 31) showed neuraminidase-resistant, trypsin-sensitive invasion, characteristic of the pathway mediated by an unknown parasite ligand and erythrocyte receptor "X." The neuraminidase-sensitive, trypsin-sensitive phenotype consistent with invasion mediated by the binding of parasite ligand erythrocyte binding antigen 175 to glycophorin A, the most common invasion profile in a previous study of Gambian field isolates, was seen in only 3 of 31 Kenyan isolates. No particular invasion profile was associated with severe P. falciparum malaria, and there was no significant difference in the levels of inhibition by the various enzyme treatments between isolates from children with severe malaria and those from children with uncomplicated malaria (P, >0.1 for all enzymes; Mann-Whitney U test). These results do not support the hypothesis that differences in invasion phenotypes play an important role in malaria virulence and indicate that considerable gaps remain in our knowledge of the molecular basis of invasion pathways in natural P. falciparum infections.

Two potential malaria virulence factors, parasite multiplication rate (PMR) and red blood cell selectivity (measured as selectivity index [SI]), were assessed in Plasmodium falciparum clinical isolates from Mali and Kenya. At both sites, PMRs were low (Kenya median = 2.2, n = 33; Mali median = 2.6, n = 61) and did not differ significantly between uncomplicated and severe malaria cases. Malian isolates from hyperparasitemic patients had significantly lower PMRs (median = 1.8, n = 19) than other Malian isolates (uncomplicated malaria median = 3.1, n = 23; severe malaria median = 2.8, n = 19; P = 0.03, by Kruskal-Wallis test). Selective invasion occurred at both sites (Kenya geometric mean SI = 1.9, n = 98; Mali geometric mean SI = 1.6, n = 104), and there was no significant association between the SI and malaria severity. Therefore, in contrast to previous results from Thailand, we found no association of PMR and SI with malaria severity in African children. This raises the possibility of differences in the mechanisms of malaria virulence between sub-Saharan Africa and Asia.

The influence of body size of Anopheles gambiae s.s., Anopheles arabiensis, Anopheles merus, and Anopheles funestus on the transmission of Plasmodium falciparum was studied at 3 sites along the Kenyan coast. Adult mosquitoes were collected inside houses by pyrethrum spray collection (PSC) from April to September 2001. Wing length was measured microscopically to the nearest 0.01 mm as an index of mosquito body size. The P. falciparum circumsporozoite protein (CSP) was detected by enzyme-linked immunosorbent assay technique. A total of 1715 anopheline mosquitoes were collected, of which 785 (45.77%) were An. gambiae s.s., 54 (3.15%) An. arabiensis, An. merus 27 (1.57%), and 849 (49.5%) were An. funestus. The mean wing length for An. gambiae s.s. was 2.94 mm and that of An. funestus was 2.50 mm. There was no site-to-site variation in the body size of An. gambiae or An. funestus. There was no significant difference in wing length between sporozoite-infected and uninfected An. gambiae s.s., and the same was found for An. funestus. At the 3 rural coastal sites in Kenya, the efficiency of malaria parasite transmission does not appear to be influenced by variation in vector body size.

We studied the effects of high temperature, 30 and 32 versus 27 C on early Plasmodium falciparum development in Anopheles gambiae experimentally infected with gametocytes from 30 volunteers with mean density of 264.1 gametocytes/microl blood (range: 16-1,536/microl). From several batches of mosquitoes, fed by membrane feeding, midguts of individual mosquitoes were dissected at 24 hr for ookinete enumeration and at 7 days to quantify oocysts. There were temperature-related differences in mean ookinete intensity per mosquito midgut, with 9.71 +/- 1.6 at 27 C, 9.85 +/- 2.32 at 30 C, and 3.89 +/- 0.81 at 32 C. The prevalence of oocyst infection decreased with an increase in temperatures from 15.9 to 8.5 to 6.4% at 27, 30, and 32 C, respectively. The average oocyst intensities for the infected mosquitoes increased with temperatures from 2.9 at 27 C to 3.5 at 30 C, and to 3.3 at 32 C. However, the success of infections was reduced at 30 and 32 C, and resulted in greater losses during consecutive inter-stage parasite development. The most significant impact of high temperatures occurred at the transition between macrogametocytes and ookinetes, whereas the transition between ookinetes and oocysts apparently was not affected. In contrast to other reports, exposure of mosquitoes infected with natural parasites to high temperatures did not eliminate preoocyst stages, as has been observed from laboratory studies using the NF-54 strain of P. falciparum. This observation of parasite resistance to high temperatures is consistent with the natural situation in tropical environments where perennial malaria transmission occurs during hot dry seasons.

A total of 1,480 Anopheles gambiae sensu lato and 439 An. funestus, collected from 30 sites along the Kenyan coast, were tested by direct enzyme-linked immunosorbent assay (ELISA) for blood-meal identification. Overall, the enzyme-linked immunosorbent assay (ELISA) identified 92 and 87% of the samples tested in An. gambiae s.l. and An. funestus, respectively. Of these, human IgG was detected in 98.97% (n = 1,347) of An. gambiae s.l. and 99.48% (n = 379) of An. funestus. Only 14 (1.03%) of the An. gambiae s.l. had fed on other vertebrate hosts tested, which were bovines, chickens, and goats. Additionally, only 2 An. funestus had fed on goats. In all the 28 sites that had bloodfed mosquitoes, An. gambiae s.l. had a human blood index greater than 0.9. Twenty-five of these sites had a human blood index greater than 0.9 for An. funestus, while the other 3 sites had no bloodfed mosquitoes. The An. gambiae s.l. were tested by polymerase chain reaction (PCR) for species identification. A total of 338 were An. gambiae s.s., 79 were An. arabiensis, and 12 were An. merus. The human blood index was 0.96, 0.91, and 1.0 for An. gambiae s.s., An. arabiensis, and An. merus, respectively. The Plasmodium falciparum sporozoite infection rates were 6.2% for species in the An. gambiae complex and 3.7% for An. funestus. These results emphasize that An. funestus and members of the An. gambiae complex on the Kenyan coast are highly anthropophilic, with nearly all specimens feeding on humans during every blood meal. The results further demonstrated active transmission of P. falciparum sporozoites by the primary vector species. This study suggests that the use of insecticide-treated nets will be effective for controlling biting mosquitoes inside houses along the coast of Kenya.

Platelet-endothelial cell adhesion molecule-1 or CD31 (PECAM-1/CD31) is a receptor recognized by Plasmodium falciparum-parasitized erythrocytes (pRBCs). Fluorescence-labeled soluble recombinant PECAM-1/CD31 (sPECAM-1/CD31) is shown to bind to the surface of P. falciparum-infected erythrocytes on up to 70% of the cells. Binding is blocked by the addition of the unlabeled receptor in a dose-dependent fashion, but not by unrelated receptor-proteins. A significant correlation was found between the binding of sPECAM-1/CD31 to pRBCs and the binding to transfected L cells expressing the receptor as seen with six different P. falciparum lines or clones. Panning of cultures on PECAM-1/CD31 transfected L cells was paralleled by an increase in the binding of sPECAM-1/CD31. The pRBCs of 54% of fresh patient-isolates bound sPECAM-1/CD31 with a mean rate of 12.9% (range = 1.1-44%). The data suggest that PECAM-1/CD31 is a common receptor recognized by wild isolates and that the soluble PECAM-1/CD31 suspension assay is a sensitive and reliable way to study PECAM-1/CD31 binding.

The variant surface antigens (VSAs) of Plasmodium falciparum-infected red blood cells are potentially important targets of naturally acquired immunity to malaria. Natural infections induce agglutinating antibodies specific to the VSA variants expressed by the infecting parasites. Previously, when different parasite isolates were tested against a panel of heterologous plasma from Kenyan children, the proportion of plasma that agglutinated the parasites (the agglutination frequency [AF]) was highly variable among isolates, suggesting the existence of rare and prevalent variants. Here, the AF of 115 isolates from Kenyan children were compared. The results show that the AF of isolates causing severe malaria were significantly higher than those of isolates causing mild malaria; and AF decreased significantly with the increasing age of the infected child. We propose that parasites causing severe disease tend to express a subset of VSA variants that are preferentially associated with infections of children with low immunity.

Recently, an association was described between the density of Plasmodium falciparum asexual parasitemia in Kenyan children and the entomologic inoculation rate (EIR) measured prior to measurement of asexual parasitemia. This study examined whether transmission pressure, as represented by the EIR, was associated with the prevalence or density of gametocytemia in Kenyan children. Each month for 19 months, a cohort of approximately 50 children was given a radical cure and enrolled in the study. Blood films were taken on days 0, 7, and 14. The EIR was calculated for the 28-day period ending 14 days prior to enrollment: the relationship between blood film data from day 7 and exposure variables was explored. We found that younger children were more likely to be gametocytemic than older children and, if gametocytemic, were more likely to have a dense gametocytemia. There was an inverse relationship between the number of infective bites per night received and prevalence but not density of gametocytemia, even after age adjustment. Concordance of gametocytemia prevalence on days 0 (64%), 7 (66%), and 14 (52%) was poor; 84% of the children were positive on at least one day. This indicates that in many subjects the detectable gametocytemia varied over the 14 days. Under these holoendemic transmission conditions, the EIR is inversely correlated with prevalence of gametocytemia, and point measurements of gametocytemia by conventional microscopy underestimate the number of infective donor hosts.

Feeding behavior was compared between infected and uninfected field-collected groups of Anopheles gambiae sensu lato and An. funestus from western Kenya. A significantly greater percentage (81%) of Plasmodium falciparum-infected An. gambiae s.l. females probed on experimental hosts (hamsters) than did uninfected females (38%). Among those females that initiated probing, there was no effect of infection status on the ability to take a bloodmeal. Plasmodium falciparum-infected An. gambiae s.l. probed more often (mean = 4.0) and for a longer time (mean = 277 sec) than did their uninfected counterparts (mean = 2.4 probes and mean probing time = 214 sec). Results for the small number of An. funestus that fed followed the same trend. Among infected An. gambiae s.l. females, there was no effect of sporozoite density on either the number of probes made or the total probing time. Among uninfected females, there was no difference in feeding behavior between nulliparous and parous females. In laboratory experiments, female age had no effect on blood-feeding behavior. Our findings provide evidence that natural malaria infection modifies the feeding behavior of Anopheles females.

The paracentric inversion polymorphisms of Anopheles gambiae and An. arabiensis populations in the Kisumu area of western Kenya were studied in relation to parameters of Plasmodium falciparum transmission. Anopheles gambiae (n = 1,387) was polymorphic for inversions b on chromosomal arm 2R and a on arm 2L, with frequencies of the inverted arrangements of 17% and 43%, respectively. Anopheles arabiensis (n = 484) was polymorphic for inversion b on chromosomal arm 2R and a on 3R, with frequencies of the inverted arrangements of 58% and 5%, respectively. Observed karyotypic frequencies did not deviate from Hardy-Weinberg equilibrium, indicating a condition of panmixia (i.e., random mating) for both species. The overall degree of intraspecific polymorphism was low, confirming findings from other zones of East Africa. No significant differences in inversion frequencies of either An. gambiae or An. arabiensis were observed, either between collecting sites or between similar sampling periods of consecutive years. At the same time, a stable, significant two-fold difference in Plasmodium infection rates was detected among An. gambiae carriers of different inversion karyotypes on chromosome 2. A significant non-uniform distribution of human- and bovid-fed specimens was also detected among the carriers of different 2Rb inversion karyotypes in indoor resting An. arabiensis. Relationships among inversion karyotypes of the two major malaria vectors in the An. gambiae complex and key factors affecting malaria transmission intensity emphasize that intraspecific variation could contribute significantly to the diversity and stability of malaria vectorial systems in Africa.

The effect of the malarial parasite, Plasmodium falciparum Welch, on the daily survival rates and longevity of Anopheles gambiae Giles sensu lato and Anopheles funestus Giles was determined for wild-caught, naturally infected females from western Kenya. Mosquitoes were collected inside houses and held in cages until death, after which they were assayed for P. falciparum circumsporozoite protein by an enzyme-linked immunosorbent assay (ELISA). Survival rates of field populations determined by parity rates were significantly higher than survival rates estimated by regression for Anopheles dying in cages. Overall, An. gambiae s.l. had a significantly higher daily mortality rate (means = 17.5%) than An. funestrus (means = 13.2%). P. falciparum ELISA infection rates, which were higher for An. gambiae s.l. (means = 19.8%; n = 1,221) than for An. funestus (means = 11.9%; n = 1,128), did not increase as a function of time for caged Anopheles. For An. gambiae s.l., there was a significant negative correlation between holding time and P. falciparum ELISA absorbance, suggesting that detectable circumsporozoite protein and perhaps the number of sporozoites may decrease with time in the vector. In western Kenya, an area where Anopheles populations often have extremely high malaria infection rates. Plasmodium infections did not reduce vector survivorship.

A study in 1984 and 1985 showed that Anopheles gambiae s.l. and An. pharoensis were the major anophelines in Mwea Irrigation Scheme, Kenya, constituting 83.86% and 15.69% of the catch respectively. Four minor species made up the remaining 0.45%. The irrigation phase of the rice cultivation cycle in August, which linked the flooding effects of the two rainy seasons, resulted in major population increases of An. pharoensis and enabled continuous breeding for up to 9 months per year. The average of mean monthly proportions of unfed, bloodfed, and gravid females was 26.6, 58.8, and 14.6% respectively. The Plasmodium falciparum sporozoite rates for An. pharoensis were 1.3% by ELISA and 0.68% by dissection, while those for An. funestus were 1.7% by ELISA and 1.25% by dissection. An. pharoensis can contribute to the epidemiology of Malaria in the Mwea area.