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"Nabie, A"
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Iron deficiency anemia in relation to pinch strength and hand dexterity in preschool children: a cross-sectional study
by
Abd-El-Nabie, Walaa A.
,
Mamdouh, Khaled Ahmed
,
Amer, Fatma Essam
in
Anemia
,
Automation
,
Blood
2024
Background
Iron deficiency anemia (IDA) constitutes a considerable nutritional problem in Egyptian preschool children. Moreover, IDA limits physical activity performance and interferes with children's development. Accordingly, we aim to investigate the correlation between IDA and hand dexterity and pinch grip strength in preschool children.
Results
This observational cross-sectional study encompassed the participation of 87 children, comprising both genders, with an age range of 5–6 years. The cohort was initially stratified into three distinct groups: Group A comprised 36 non-anemic children, group B included 25 children with mild iron-deficiency anemia (IDA), and group C consisted of 26 children with moderate IDA. After group delineation, comprehensive laboratory analyses were performed on all participants to assess for IDA, involving a thorough examination of their complete blood picture, hemoglobin (Hb) levels, serum iron levels, and serum ferritin levels. The evaluative metrics employed in this study encompassed the Bruininks-Oseretsky Test of Motor Proficiency-Second Edition (BOT-2) and the Baseline Mechanical Pinch Gauge. These instruments were utilized to assess manual dexterity and pinch strength, specifically tip-to-tip and tripod strength. This investigation revealed a positive correlation between Hb, serum iron, and serum ferritin levels with both manual dexterity and pinch strength across all three groups.
Conclusion
This study highlights that IDA negatively affects hand dexterity and pinch grip strength in preschool children. Managing IDA early is crucial for improving their physical performance and overall development.
Journal Article
Immediate effect of maximal treadmill walking on muscle fatigue and postural stability in children with cerebral palsy
by
Attia, Maha A.
,
Abd El-Nabie, Walaa A.
in
Cerebral palsy
,
Children with disabilities
,
Fitness equipment
2019
Aim
Postural instability and muscle fatigue are from elementary causes of deteriorations in children with cerebral palsy (CP). The aim of this study was to investigate the immediate effect of maximal treadmill walking on muscle fatigue and postural stability in children with hemiplegic CP.
Patients and methods
Thirty (17 boys and 13 girls) children with hemiplegic CP of both sexes, aged from 5 to 11years, participatedin this study. Muscle fatigue and postural stability were assessed for every child by using isokinetic dynamometer and pediatric reaching test, respectively, before and after maximal treadmill walking at two separated sessions.
Results
The results showed that there were no significant differences in fatigue index (
P
=0.33 and 0.1), peak torque of quadriceps and hamstring muscles (
P
=0.52 and 0.14), and anterior and lateral reaching tests of postural stability (
P
=0.46 and 0.63) before and after maximal treadmill walking.
Conclusion
Maximal treadmill walking does not cause muscle fatigue or postural instability in children with hemiplegic CP.
Journal Article
Safety and immunogenicity of the two-dose heterologous Ad26.ZEBOV and MVA-BN-Filo Ebola vaccine regimen in children in Sierra Leone: a randomised, double-blind, controlled trial
2022
Children account for a substantial proportion of cases and deaths from Ebola virus disease. We aimed to assess the safety and immunogenicity of a two-dose heterologous vaccine regimen, comprising the adenovirus type 26 vector-based vaccine encoding the Ebola virus glycoprotein (Ad26.ZEBOV) and the modified vaccinia Ankara vector-based vaccine, encoding glycoproteins from the Ebola virus, Sudan virus, and Marburg virus, and the nucleoprotein from the Tai Forest virus (MVA-BN-Filo), in a paediatric population in Sierra Leone.
This randomised, double-blind, controlled trial was done at three clinics in Kambia district, Sierra Leone. Healthy children and adolescents aged 1–17 years were enrolled in three age cohorts (12–17 years, 4–11 years, and 1–3 years) and randomly assigned (3:1), via computer-generated block randomisation (block size of eight), to receive an intramuscular injection of either Ad26.ZEBOV (5 × 1010 viral particles; first dose) followed by MVA-BN-Filo (1 × 108 infectious units; second dose) on day 57 (Ebola vaccine group), or a single dose of meningococcal quadrivalent (serogroups A, C, W135, and Y) conjugate vaccine (MenACWY; first dose) followed by placebo (second dose) on day 57 (control group). Study team personnel (except for those with primary responsibility for study vaccine preparation), participants, and their parents or guardians were masked to study vaccine allocation. The primary outcome was safety, measured as the occurrence of solicited local and systemic adverse symptoms during 7 days after each vaccination, unsolicited systemic adverse events during 28 days after each vaccination, abnormal laboratory results during the study period, and serious adverse events or immediate reportable events throughout the study period. The secondary outcome was immunogenicity (humoral immune response), measured as the concentration of Ebola virus glycoprotein-specific binding antibodies at 21 days after the second dose. The primary outcome was assessed in all participants who had received at least one dose of study vaccine and had available reactogenicity data, and immunogenicity was assessed in all participants who had received both vaccinations within the protocol-defined time window, had at least one evaluable post-vaccination sample, and had no major protocol deviations that could have influenced the immune response. This study is registered at ClinicalTrials.gov, NCT02509494.
From April 4, 2017, to July 5, 2018, 576 eligible children or adolescents (192 in each of the three age cohorts) were enrolled and randomly assigned. The most common solicited local adverse event during the 7 days after the first and second dose was injection-site pain in all age groups, with frequencies ranging from 0% (none of 48) of children aged 1–3 years after placebo injection to 21% (30 of 144) of children aged 4–11 years after Ad26.ZEBOV vaccination. The most frequently observed solicited systemic adverse event during the 7 days was headache in the 12–17 years and 4–11 years age cohorts after the first and second dose, and pyrexia in the 1–3 years age cohort after the first and second dose. The most frequent unsolicited adverse event after the first and second dose vaccinations was malaria in all age cohorts, irrespective of the vaccine types. Following vaccination with MenACWY, severe thrombocytopaenia was observed in one participant aged 3 years. No other clinically significant laboratory abnormalities were observed in other study participants, and no serious adverse events related to the Ebola vaccine regimen were reported. There were no treatment-related deaths. Ebola virus glycoprotein-specific binding antibody responses at 21 days after the second dose of the Ebola virus vaccine regimen were observed in 131 (98%) of 134 children aged 12–17 years (9929 ELISA units [EU]/mL [95% CI 8172–12 064]), in 119 (99%) of 120 aged 4–11 years (10 212 EU/mL [8419–12 388]), and in 118 (98%) of 121 aged 1–3 years (22 568 EU/mL [18 426–27 642]).
The Ad26.ZEBOV and MVA-BN-Filo Ebola vaccine regimen was well tolerated with no safety concerns in children aged 1–17 years, and induced robust humoral immune responses, suggesting suitability of this regimen for Ebola virus disease prophylaxis in children.
Innovative Medicines Initiative 2 Joint Undertaking and Janssen Vaccines & Prevention BV.
Journal Article
Safety and long-term immunogenicity of the two-dose heterologous Ad26.ZEBOV and MVA-BN-Filo Ebola vaccine regimen in adults in Sierra Leone: a combined open-label, non-randomised stage 1, and a randomised, double-blind, controlled stage 2 trial
The Ebola epidemics in west Africa and the Democratic Republic of the Congo highlight an urgent need for safe and effective vaccines to prevent Ebola virus disease. We aimed to assess the safety and long-term immunogenicity of a two-dose heterologous vaccine regimen, comprising the adenovirus type 26 vector-based vaccine encoding the Ebola virus glycoprotein (Ad26.ZEBOV) and the modified vaccinia Ankara vector-based vaccine, encoding glycoproteins from Ebola virus, Sudan virus, and Marburg virus, and the nucleoprotein from the Tai Forest virus (MVA-BN-Filo), in Sierra Leone, a country previously affected by Ebola.
The trial comprised two stages: an open-label, non-randomised stage 1, and a randomised, double-blind, controlled stage 2. The study was done at three clinics in Kambia district, Sierra Leone. In stage 1, healthy adults (aged ≥18 years) residing in or near Kambia district, received an intramuscular injection of Ad26.ZEBOV (5 × 1010 viral particles) on day 1 (first dose) followed by an intramuscular injection of MVA-BN-Filo (1 × 108 infectious units) on day 57 (second dose). An Ad26.ZEBOV booster vaccination was offered at 2 years after the first dose to stage 1 participants. The eligibility criteria for adult participants in stage 2 were consistent with stage 1 eligibility criteria. Stage 2 participants were randomly assigned (3:1), by computer-generated block randomisation (block size of eight) via an interactive web-response system, to receive either the Ebola vaccine regimen (Ad26.ZEBOV followed by MVA-BN-Filo) or an intramuscular injection of a single dose of meningococcal quadrivalent (serogroups A, C, W135, and Y) conjugate vaccine (MenACWY; first dose) followed by placebo on day 57 (second dose; control group). Study team personnel, except those with primary responsibility for study vaccine preparation, and participants were masked to study vaccine allocation. The primary outcome was the safety of the Ad26.ZEBOV and MVA-BN-Filo vaccine regimen, which was assessed in all participants who had received at least one dose of study vaccine. Safety was assessed as solicited local and systemic adverse events occurring in the first 7 days after each vaccination, unsolicited adverse events occurring in the first 28 days after each vaccination, and serious adverse events or immediate reportable events occurring up to each participant's last study visit. Secondary outcomes were to assess Ebola virus glycoprotein-specific binding antibody responses at 21 days after the second vaccine in a per-protocol set of participants (ie, those who had received both vaccinations within the protocol-defined time window, had at least one evaluable post-vaccination sample, and had no major protocol deviations that could have influenced the immune response) and to assess the safety and tolerability of the Ad26.ZEBOV booster vaccination in stage 1 participants who had received the booster dose. This study is registered at ClinicalTrials.gov, NCT02509494.
Between Sept 30, 2015, and Oct 19, 2016, 443 participants (43 in stage 1 and 400 in stage 2) were enrolled; 341 participants assigned to receive the Ad26.ZEBOV and MVA-BN-Filo regimen and 102 participants assigned to receive the MenACWY and placebo regimen received at least one dose of study vaccine. Both regimens were well tolerated with no safety concerns. In stage 1, solicited local adverse events (mostly mild or moderate injection-site pain) were reported in 12 (28%) of 43 participants after Ad26.ZEBOV vaccination and in six (14%) participants after MVA-BN-Filo vaccination. In stage 2, solicited local adverse events were reported in 51 (17%) of 298 participants after Ad26.ZEBOV vaccination, in 58 (24%) of 246 after MVA-BN-Filo vaccination, in 17 (17%) of 102 after MenACWY vaccination, and in eight (9%) of 86 after placebo injection. In stage 1, solicited systemic adverse events were reported in 18 (42%) of 43 participants after Ad26.ZEBOV vaccination and in 17 (40%) after MVA-BN-Filo vaccination. In stage 2, solicited systemic adverse events were reported in 161 (54%) of 298 participants after Ad26.ZEBOV vaccination, in 107 (43%) of 246 after MVA-BN-Filo vaccination, in 51 (50%) of 102 after MenACWY vaccination, and in 39 (45%) of 86 after placebo injection. Solicited systemic adverse events in both stage 1 and 2 participants included mostly mild or moderate headache, myalgia, fatigue, and arthralgia. The most frequent unsolicited adverse event after the first dose was headache in stage 1 and malaria in stage 2. Malaria was the most frequent unsolicited adverse event after the second dose in both stage 1 and 2. No serious adverse event was considered related to the study vaccine, and no immediate reportable events were observed. In stage 1, the safety profile after the booster vaccination was not notably different to that observed after the first dose. Vaccine-induced humoral immune responses were observed in 41 (98%) of 42 stage 1 participants (geometric mean binding antibody concentration 4784 ELISA units [EU]/mL [95% CI 3736–6125]) and in 176 (98%) of 179 stage 2 participants (3810 EU/mL [3312–4383]) at 21 days after the second vaccination.
The Ad26.ZEBOV and MVA-BN-Filo vaccine regimen was well tolerated and immunogenic, with persistent humoral immune responses. These data support the use of this vaccine regimen for Ebola virus disease prophylaxis in adults.
Innovative Medicines Initiative 2 Joint Undertaking and Janssen Vaccines & Prevention BV.
Journal Article
Influence of different host blood meal sources on the reproductive outcomes in Anopheles gambiae: Enhancing fecundity in a mass rearing environment
by
Wekesa, Celestine N.
,
Bayoh, Nabie M.
,
Otieno-Ayayo, Z. Ngalo
in
Animals
,
Anopheles
,
Anopheles - physiology
2025
Identification of blood sources for maximum production of Anopheles mosquitoes is an important consideration for colony maintenance which involves mass rearing. High feeding rates, eggs production, hatching rates, larval, pupal, and adult survivorship are essential parameters to consider when selecting a blood host for mass production of An. gambiae. Here, we investigated the feeding success, reproduction performance and survivorship of An. gambiae when fed on blood from five different hosts: cow, goat, sheep, pig, and chicken compared to human blood. There was significant variations in feeding success (F 5, 18 = 35.34, p < .001), egg laying (F 5,18 = 12.57, p < .001), number of eggs laid (F 5, 18 = 34.23 p < .001), egg hatchability (F 5, 114 = 37.63, p < .001), pupation time (F 5,18 = 5.532763, p = 0.0029) and pupation rates (F 5,18 = 8.26, p < .001). Feeding success was highest in human blood meal (Mean = 125.25 ± 3.86), followed by pig blood meal (Mean = 123 ± 7.93), with no statistically significant difference between the two. The highest proportion of females that laid eggs were those fed on human blood (Mean = 36.50 ± 2.08) followed by those fed on chicken blood meals (Mean = 27.50 ± 5.44) and then pig blood meal (Mean = 26.25 ± 2.87). The mean number of eggs laid per mosquito was highest among those fed on human blood meal (111.65 ± 5.74) followed by those fed on pig blood meal (100.46 ± 6.36). The most favorable outcomes were observed with human blood for hatchability (88.35 ± 5.61%), pig blood for pupation percentage (Mean = 83.50 ± 4.79), and goat blood for pupation time (9.79 ± 0.41 days). Larval survival rates did not significantly differ among blood meal sources (F 5,92 = 0.13, p = 0.985). Nonetheless, the highest survival rate was observed with pig blood meal (Mean = 0.57 ± 0.11). Survival rates of adult F 1 varied significantly across blood meals ( F 6,346 = 133.19, p < .001), with human blood meal showing the highest survival rate (Mean = 0.73 ± 0.04). However, pig blood meal (56 days) demonstrated the longest survival period, close to human blood meal (57 days). This study revealed pig blood as an excellent alternative to human blood meal for the mass production of An. gambiae.
Journal Article
Spatial and temporal variation in the kdr allele L1014S in Anopheles gambiae s.s. and phenotypic variability in susceptibility to insecticides in Western Kenya
by
Nabie Bayoh, M
,
Kamau, Luna
,
Atieli, Francis
in
Alleles
,
Amino Acid Substitution - genetics
,
Animals
2011
Background
Malaria vector control in Africa depends upon effective insecticides in bed nets and indoor residual sprays. This study investigated the extent of insecticide resistance in
Anopheles gambiae
s.l.,
Anopheles gambiae
s.s. and
Anopheles arabiensis
in western Kenya where ownership of insecticide-treated bed nets has risen steadily from the late 1990s to 2010. Temporal and spatial variation in the frequency of a
knock down resistance
(
kdr
) allele in
A. gambiae
s.s. was quantified, as was variation in phenotypic resistance among geographic populations of
A. gambiae
s.l.
Methods
To investigate temporal variation in
kdr
frequency, individual specimens of
A. gambiae
s.s. from two sentinel sites were genotyped using RT-PCR from 1996-2010. Spatial variation in
kdr
frequency, species composition, and resistance status were investigated in additional populations of
A. gambiae
s.l. sampled in western Kenya in 2009 and 2010. Specimens were genotyped for
kdr
as above and identified to species via conventional PCR. Field-collected larvae were reared to adulthood and tested for insecticide resistance using WHO bioassays.
Results
Anopheles gambiae
s.s. showed a dramatic increase in
kdr
frequency from 1996 - 2010, coincident with the scale up of insecticide-treated nets. By 2009-2010, the
kdr
L1014S allele was nearly fixed in the
A. gambiae
s.s. population, but was absent in
A. arabiensis
. Near Lake Victoria,
A. arabiensis
was dominant in samples, while at sites north of the lake
A. gambiae
s.s was more common but declined relative to
A. arabiensis
from 2009 to 2010. Bioassays demonstrated that
A. gambiae
s.s. had moderate phenotypic levels of resistance to DDT, permethrin and deltamethrin while
A. arabiensis
was susceptible to all insecticides tested.
Conclusions
The
kdr
L1014S allele has approached fixation in
A. gambiae
s.s. populations of western Kenya, and these same populations exhibit varying degrees of phenotypic resistance to DDT and pyrethroid insecticides. The near absence of
A. gambiae
s.s. from populations along the lakeshore and the apparent decline in other populations suggest that insecticide-treated nets remain effective against this mosquito despite the increase in
kdr
allele frequency. The persistence of
A. arabiensis
, despite little or no detectable insecticide resistance, is likely due to behavioural traits such as outdoor feeding and/or feeding on non-human hosts by which this species avoids interaction with insecticide-treated nets.
Journal Article
Persistently high estimates of late night, indoor exposure to malaria vectors despite high coverage of insecticide treated nets
2014
BACKGROUND: It has been speculated that widespread and sustained use of insecticide treated bed nets (ITNs) for over 10 years in Asembo, western Kenya, may have selected for changes in the location (indoor versus outdoor) and time (from late night to earlier in the evening) of biting of the predominant species of human malaria vectors (Anopheles funestus, Anopheles gambiae sensu stricto, and Anopheles arabiensis). METHODS: Mosquitoes were collected by human landing catches over a six week period in June and July, 2011, indoors and outdoors from 17 h to 07 h, in 75 villages in Asembo, western Kenya. Collections were separated by hour of the night, and mosquitoes were identified to species and tested for sporozoite infection with Plasmodium falciparum. A subset was dissected to determine parity. Human behavior (time going to bed and rising, time spent indoors and outdoors) was quantified by cross-sectional survey. Data from past studies of a similar design and in nearby settings, but conducted before the ITN scale up commenced in the early 2000s, were compared with those from the present study. RESULTS: Of 1,960 Anopheles mosquitoes collected in 2011, 1,267 (64.6%) were morphologically identified as An. funestus, 663 (33.8%) as An. gambiae sensu lato (An. gambiae s.s. and An. arabiensis combined), and 30 (1.5%) as other anophelines. Of the 663 An. gambiae s.l. collected, 385 were successfully tested by PCR among which 235 (61.0%) were identified as An. gambiae s.s. while 150 (39.0%) were identified as An. arabiensis. Compared with data collected before the scale-up of ITNs, daily entomological inoculation rates (EIRs) were consistently lower for An. gambiae s.l. (indoor EIR = 0.432 in 1985–1988, 0.458 in 1989–1990, 0.023 in 2011), and An. arabiensis specifically (indoor EIR = 0.532 in 1989–1990, 0.039 in 2009, 0.006 in 2011) but not An. funestus (indoor EIR = 0.029 in 1985–1988, 0.147 in 1989–1990, 0.010 in 2009 and 0.103 in 2011). Sporozoite rates were lowest in 2009 but rose again in 2011. Compared with data collected before the scale-up of ITNs, An. arabiensis and An. funestus were more likely to bite outdoors and/or early in the evening (p < 0.001 for all comparisons). However, when estimates of human exposure that would occur indoors (πᵢ) or while asleep (πₛ) in the absence of an ITN were generated based on human behavioral patterns, the changes were modest with >90% of exposure of non-ITN users to mosquito bites occurring while people were indoors in all years. The proportion of bites occurring among non-ITN users while they were asleep was ≥90% for all species except for An. arabiensis. For this species, 97% of bites occurred while people were asleep in 1989–1990 while in 2009 and 2011, 80% and 84% of bites occurred while people were asleep for those not using ITNs. Assuming ITNs prevent a theoretical maximum of 93.7% of bites, it was estimated that 64-77% of bites would have occurred among persons using nets while they were asleep in 1989–1990, while 20-52% of bites would have occurred among persons using nets while they were asleep in 2009 and 2011. CONCLUSIONS: This study found no evidence to support the contention that populations of Anopheles vectors of malaria in Asembo, western Kenya, are exhibiting departures from the well-known pattern of late night, indoor biting characteristic of these typically highly anthropophilic species. While outdoor, early evening transmission likely does occur in western Kenya, the majority of transmission still occurs indoors, late at night. Therefore, malaria control interventions such as ITNs that aim to reduce indoor biting by mosquitoes should continue to be prioritized.
Journal Article
The Effect of Indoor Residual Spraying on the Prevalence of Malaria Parasite Infection, Clinical Malaria and Anemia in an Area of Perennial Transmission and Moderate Coverage of Insecticide Treated Nets in Western Kenya
2016
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).
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.
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.
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.
Journal Article
Reduced mosquito survival in metal-roof houses may contribute to a decline in malaria transmission in sub-Saharan Africa
by
Kandeh, Balla
,
Kirby, Matthew J.
,
Macdonald, Mike
in
631/158/1469
,
692/699/255/1629
,
Africa South of the Sahara
2019
In The Gambia, metal-roof houses were hotter during the day than thatched-roof houses. After 24 h, the mortality of
Anopheles gambiae
, the principal African malaria vector, was 38% higher in metal-roof houses than thatched ones. During the day, mosquitoes in metal-roof houses moved from the hot roof to cooler places near the floor, where the temperature was still high, reaching 35 °C. In laboratory studies, at 35 °C few mosquitoes survived 10 days, the minimum period required for malaria parasite development. Analysis of epidemiological data showed there was less malaria and lower vector survival rates in Gambian villages with a higher proportion of metal roofs. Our findings are consistent with the hypothesis that the indoor climate of metal-roof houses, with higher temperatures and lower humidity, reduces survivorship of indoor-resting mosquitoes and may have contributed to the observed reduction in malaria burden in parts of sub-Saharan Africa.
Journal Article
Anopheles gambiae: historical population decline associated with regional distribution of insecticide-treated bed nets in western Nyanza Province, Kenya
2010
Background
High coverage of insecticide-treated bed nets in Asembo and low coverage in Seme, two adjacent communities in western Nyanza Province, Kenya; followed by expanded coverage of bed nets in Seme, as the Kenya national malaria programme rolled out; provided a natural experiment for quantification of changes in relative abundance of two primary malaria vectors in this holoendemic region. Both belong to the
Anopheles gambiae sensu lato (s.l.)
species complex, namely
A. gambiae sensu stricto (s.s.)
and
Anopheles arabiensis
. Historically, the former species was proportionately dominant in indoor resting collections of females.
Methods
Data of the relative abundance of adult
A. gambiae s.s.
and
A. arabiensis
sampled from inside houses were obtained from the literature from 1970 to 2002 for sites west of Kisumu, Kenya, to the region of Asembo ca. 50 km from the city. A sampling transect was established from Asembo (where bed net use was high due to presence of a managed bed net distribution programme) eastward to Seme, where no bed net programme was in place. Adults of
A. gambiae s.l.
were sampled from inside houses along the transect from 2003 to 2009, as were larvae from nearby aquatic habitats, providing data over a nearly 40 year period of the relative abundance of the two species. Relative proportions of
A. gambiae s.s.
and
A. arabiensis
were determined for each stage by identifying species by the polymerase chain reaction method. Household bed net ownership was measured with surveys during mosquito collections. Data of blood host choice, parity rate, and infection rate for
Plasmodium falciparum
in
A. gambiae s.s.
and
A. arabiensis
were obtained for a sample from Asembo and Seme from 2005.
Results
Anopheles gambiae s.s.
adult females from indoor collections predominated from 1970 to 1998 (ca. 85%). Beginning in 1999,
A. gambiae
s.s decreased proportionately relative to
A. arabiensis
, then precipitously declined to rarity coincident with increased bed net ownership as national bed net distribution programmes commenced in 2004 and 2006. By 2009,
A. gambiae s.s.
comprised proportionately ca. 1% of indoor collections and
A. arabiensis
99%. In Seme compared to Asembo in 2003, proportionately more larvae were
A. gambiae s.s.
, larval density was higher, and more larval habitats were occupied. As bed net use rose in Seme, the proportion of
A. gambiae
larvae declined as well. These trends continued to 2009. Parity and malaria infection rates were lower in both species in Asembo (high bed net use) compared to Seme (low bed net use), but host choice did not vary within species in both communities (predominantly cattle for
A. arabiensis
, humans for
A. gambiae s.s.
).
Conclusions
A marked decline of the
A. gambiae s.s.
population occurred as household ownership of bed nets rose in a region of western Kenya over a 10 year period. The increased bed net coverage likely caused a mass effect on the composition of the
A. gambiae s.l.
species complex, resulting in the observed proportionate increase in
A. arabiensis
compared to its closely related sibling species,
A. gambiae s.s.
These observations are important in evaluating the process of regional malaria elimination, which requires sustained vector control as a primary intervention.
Journal Article