Letter to the editors.
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Bedding and Linens↗
Biomedical subjects
William A Hawley
Publications and source records attributed to William A Hawley.
Distribution, description, and local knowledge of larval habitats of Anopheles gambiae s.l. in a village in western Kenya.
A sampling census revealed 104 aquatic habitats of 6 types for Anopheles gambiae s.l. larvae in a village in western Kenya, namely burrow pits, drainage channels, livestock hoof prints, rain pools, tire tracks, and pools in streambeds. Most habitats were created by human activity and were highly clustered in dispersion pattern within the village landscape. Landscape analysis revealed that six of forty-seven 0.09 km(2) cells superimposed over the village harbored 65% of all habitats. Focus group discussions and in-depth interviews with villagers revealed the extent of knowledge of the village residents of larval habitats, mosquito sources in the local environment, and what might be done to prevent mosquito breeding. Participants did not associate specific habitats with anopheline larvae, expressed reluctance to eliminate habitats because they were sources of domestic water supply, but indicated willingness to participate in a source reduction program if support were available.
Animals↗
Pupal habitat productivity of Anopheles gambiae complex mosquitoes in a rural village in western Kenya.
The productivity of larval habitats of the malaria vector Anopheles gambiae for pupae (the stage preceding adult metamorphosis) is poorly known, yet adult emergence from habitats is the primary determinant of vector density. To assess it, we used absolute sampling methods in four studies involving daily sampling for 25 days in 6 habitat types in a village in western Kenya. Anopheles gambiae s.s. comprised 82.5% of emergent adults and Anopheles arabiensis the remainder. Pupal production occurred from a subset of habitats, primarily soil burrow pits, and was discontinuous in time, even when larvae occupied all habitats continuously. Habitat stability was positively associated with pupal productivity. In a dry season, pupal productivity was distributed between burrow pits and pools in streambeds. Overall, these data support the notion that source reduction measures against recognizably productive habitats would be a useful component of an integrated management program for An. gambiae in villages.
Animals↗
Burden of malaria at community level in children less than 5 years of age in Togo.
A community-based baseline cross-sectional survey was conducted in three districts in Togo in September 2004 as part of a multidisciplinary evaluation of the impact of the Togo National Integrated Child Health Campaign. During this campaign, long-lasting-insecticide-treated bed nets (LLITNs) were distributed to households with children between 9 months and 5 years of age throughout the country in December 2004. The pre-intervention survey provided baseline malaria and anemia prevalence in children < 5 years of age during peak malaria transmission. Of 2,532 enrolled children from 1,740 households, 62.2% (1,352/2,172) were parasitemic and 84.4% (2,129/2,524) were anemic (hemoglobin < 11 g/dL). Moderate-to-severe anemia (< 8.0 g/dL) was found in 21.7% (543/2,524), with a peak prevalence in children 6-17 months of age and was strongly correlated with parasitemia (OR = 2.3, 95% CI: 1.8-2.5). Net ownership (mainly untreated) was 225/2,532 (8.9%). Subsequent nation-wide introduction of LLITNs and the introduction of artemisinin-based combination therapy have the potential to markedly reduce this burden of malaria.
Anemia↗
Successful integration of insecticide-treated bed net distribution with mass drug administration in Central Nigeria.
In Africa anopheline mosquitoes transmit malaria and lymphatic filariasis (LF); insecticide-treated bed nets significantly reduce transmission of both. Insecticide-treated bed net provision to children under 5 (U5) and pregnant women (PW) is a major goal of malaria control initiatives, but use in Africa remains low because of cost and logistics. We therefore integrated insecticide-treated bed net distribution with the 2004 LF/onchocerciasis mass drug administration (MDA) program in Central Nigeria. Community volunteers distributed 38,600 insecticide-treated bed nets, while simultaneously treating 150,800 persons with ivermectin/albendazole (compared with 135,600 in 2003). This was subsequently assessed with a 30-cluster survey. Among surveyed households containing U5/PW, 80% (95% CI, 72-87%) owned > or = 1 insecticide-treated bed net, a 9-fold increase from 2003. This first linkage of insecticide-treated bed net distribution with mass drug administration resulted in substantial improvement in insecticide-treated bed net ownership and usage, without adversely affecting mass drug administration coverage. Such integration allowed two programs to share resources while realizing mutual benefit, and is one model for rapidly improving insecticide-treated bed net coverage objectives.
Adolescent↗
Larval development of the molecular forms of Anopheles gambiae (Diptera: Culicidae) in different habitats: a transplantation experiment.
We compared the development of the molecular forms of Anopheles gambiae s.s. in different larval habitats. First stage larvae (L1s) of wild-caught females were placed into cages in natural habitats of the M form (rice fields) or the S form (puddles/ quarries). Each cage was covered with cloth, allowing exchange of water, solutes, and small particles, including microorganisms, and was seeded with 100 L1s of a single form (M or S) or by a mixture of 50:50 of M and S forms. Emergence success of both forms in puddles and quarries was three-fold higher than in the rice fields. The emergence rate of the S form was higher than that of the M form in both habitats, but the form x habitat interaction was not significant. In temporary larval sites such as puddles, emergence success of the M form was lower in mixed cages than in single form cages, whereas the reverse was true for the S form, suggesting competition between the forms. The median developmental time was not significantly different between forms. Although these findings demonstrate differences between forms, they do not suggest that their spatial segregation is determined by differences in their exploitation of the physical and chemical conditions in these environments. These results should be regarded with caution because small numbers of first stage larvae could pass through the cloth of the cages.
Animals↗
Laboratory wash resistance of long-lasting insecticidal nets.
Long-lasting insecticidal nets (LLINs) may eliminate the need for retreatment of mosquito nets used for the control of malaria and other vector-borne diseases. The efficacy of LLINs after repeated washing under laboratory conditions has been used to predict long-lasting efficacy under field conditions. We evaluated under laboratory conditions the wash resistance of two LLINs (PermaNet 1.0, Vestergaard-Frandsen, Denmark; Olyset, Sumitomo Chemical Co., Japan), two candidate LLINs (Dawa, Siamdutch Mosquito Netting Co., Thailand; Insector, Athanor, France) and a net treated with a process designed to increase its wash resistance and compared them with conventionally treated nets (deltamethrin, 25 mg/m(2)). Nets of all six types were washed using a standard protocol and tested weekly using WHO cone bioassays with Anopheles gambiae (Kisumu strain). The PermaNet 1.0 was the most wash resistant with >50% mosquito mortality in WHO cone bioassays after as many as 20 washes. The Dawa net also retained some activity after repeated washing but exhibited wide variation in insecticide retention and biological activity. The remaining nets lost >90% of their biological activity after six washes as measured by 24-h mortality of A. gambiae in WHO cone tests. After 20 washes, all nets lost >50% of their initial insecticide concentrations except for the Olyset net. After 20 washes, nets were heated for 4 h at 60 degrees C to determine whether biological activity could be restored by heat-assisted regeneration. Only the Olyset net was regenerated by heating, with average mosquito mortality and knockdown in WHO cone tests rising to >90% after heating for 4 h at 60 degrees C. However, regeneration of the biological activity of Olyset nets that had been washed three times did not occur at 30 degrees C or 35 degrees C after 12 weeks. The wash resistance of these LLINs corresponded well to their retention of biological activity observed in a field trial, suggesting that wash resistance may be a good predictor of the longevity of insecticidal activity of LLINs under field conditions.
Animals↗
Evaluation of long-lasting insecticidal nets after 2 years of household use.
Development of long-lasting insecticidal nets (LLINs) may eliminate the need for insecticide retreatment of ITNs. While two LLINs (Olyset, Sumitomo Chemical Co., Japan; and PermaNet 1.0, Vestergaard-Frandsen, Denmark) have received recommendations from the World Health Organization Pesticide Evaluation Scheme, field-testing under normal use has been limited. We used a survival analysis approach to compare time to net failure of conventional polyester bednets treated only with deltamethrin to two LLINs and two candidate LLINs (Olyset; PermaNet; Insector, Athanor, France; and Dawa, Siamdutch Mosquito Netting Co., Thailand). Additionally, we evaluated nets treated with a process designed to increase the wash-durability of permethrin-treated nets through the addition of cyclodextrin (a starch) in the treatment process. Houses in western Kenya were randomly assigned to one of the six net types and nets were distributed to cover all sleeping spaces. Households were visited monthly to assess reported side effects in inhabitants and washing frequency. Nets were evaluated for insecticidal activity by periodic WHO cone bioassays with mortality assessed at 24 h. Nets with bioassay mortality <70% were assayed monthly until failure, defined as the first of two consecutive bioassay mortality rates <50%. Time to failure was analyzed using an extended Cox Proportional Hazards model controlling for the cumulative number of washes. We distributed 314 nets to 177 households in June-July 2002; 22 nets (7.0%) were lost to follow-up and 196 (62.4%) failed during the first 2 years of the evaluation. Controlling for cumulative number of washes, PermaNet 1.0 [Hazard Ratio (HR) 0.14, 95% Confidence Interval (CI) 0.06-0.31] had a significantly lower risk of failure than conventional nets while Insector had a significantly higher risk of failure (HR 2.57, 95% CI 1.06-4.15). The risks of failure of the remaining nets (Olyset: HR 1.29, 95% CI 0.79-2.10; Dawa: HR 0.58, 95% CI 0.32-1.18; cyclodextrin: HR 0.65, 95% CI 0.40-1.1) were not significantly different from that of a conventional net. PermaNet 1.0 performed significantly better than conventional nets and should be recommended to malaria control programs.
Animals↗
Factors associated with hemoglobin concentrations in pre-school children in Western Kenya: cross-sectional studies.
In sub-Saharan Africa, the etiology of anemia in early childhood is complex and multifactorial. Three community-based cross-sectional surveys were used to determine the prevalence and severity of anemia. Regression methods were used to compare mean hemoglobin (Hb) concentrations across covariate levels to identify children at risk of low Hb levels in an area with intense malaria transmission. In a random sample of 2,774 children < 36 months old, the prevalence of anemia (Hb < 11g/dL) was 76.1% and 71%, respectively, in villages without and with insecticide-treated bed nets (ITNs); severe-moderate anemia (Hb < 7 g/dL) was observed in 11% (non-ITN) and 8.3% (ITN). The prevalence of anemia, high-density malaria parasitemia (21.7%), microcytosis (34.9%), underweight (21.9%), and diarrhea (54.8%) increased rapidly from age three months onwards and remained high until 35 months of age. Multivariate analyses showed that family size, history of fever, pale body, general body weakness, diarrhea, soil-eating, concurrent fever, stunting, and malaria parasitemia were associated with mean Hb levels. Prevention of severe anemia should start early in infancy and include a combination of micronutrient supplementation, malaria control, and possibly interventions against diarrheal illness.
Anemia↗
Effect of sustained insecticide-treated bed net use on all-cause child mortality in an area of intense perennial malaria transmission in western Kenya.
We present results from a study conducted in western Kenya where all-cause child mortality was assessed among a population with high levels of sustained insecticide-treated bed net (ITN) use for up to six years. Although ITNs were associated with significant reductions in all-cause mortality among infants 1-11 months old, there was no difference in the rate of all-cause mortality among children 12-59 months old with ITNs for 2-4 years, compared historically with children from villages without ITNs, after controlling for seasonality and underlying child mortality across calendar years (adjusted hazard ratio [AHR] = 0.91, 95% confidence interval [CI] = 0.77-1.07). There was no increase in the proportion of child deaths at older ages (12-59 months old) of all child deaths within villages with ITNs for 5-6 years (48.1%) compared historically with villages without ITNs (47.9%), after controlling for seasonality (AHR = 1.03, P = 0.834). We find no evidence that sustained ITN use increased the risk of mortality in older children in this area of intense perennial malaria transmission.
Animals↗
Malaria and nutritional status among pre-school children: results from cross-sectional surveys in western Kenya.
Protein-energy malnutrition (PEM) affects millions of children in the developing world. The relationship between malaria and PEM is controversial. The goal of this study was to evaluate whether undernutrition is associated with increased or decreased malaria attributable morbidity. Three cross-sectional surveys were conducted using insecticide-treated bed nets (ITNs) among children aged 0-36 months living in an area with intense malaria transmission. Data were collected on nutritional status, recent history of clinical illness, socioeconomic status, current malaria infection status, and hemoglobin. In multivariate models, stunted children had more malaria parasitemia (odds ratio [OR] 1.98, P < 0.0001), high-density parasitemia (OR 1.84; P < 0.0001), clinical malaria (OR 1.77; P < 0.06), and severe malarial anemia (OR 2.65; P < 0.0001) than nonstunted children. The association was evident in children with mild-to-moderate (-3 < height-for-age Z-score [HAZ] < -2) and severe stunting (HAZ < -3). The cross-sectional nature of the study limits the interpretation of causality, but the data provide further observational support that the presence of undernutrition, in particular chronic undernutrition, places children at higher, not lower risk of malaria-related morbidity.
Bedding and Linens↗
Sustainability of reductions in malaria transmission and infant mortality in western Kenya with use of insecticide-treated bednets: 4 to 6 years of follow-up.
CONTEXT: Insecticide-treated bednets reduce malaria transmission and child morbidity and mortality in short-term trials, but this impact may not be sustainable. Previous investigators have suggested that bednet use might paradoxically increase mortality in older children through delayed acquisition of immunity to malaria. OBJECTIVES: To determine whether adherence to and public health benefits of insecticide-treated bednets can be sustained over time and whether bednet use during infancy increases all-cause mortality rates in older children in an area of intense perennial malaria transmission. DESIGN AND SETTING: A community randomized controlled trial in western Kenya (phase 1: January 1997 to February 2000) followed by continued surveillance of adherence, entomologic parameters, morbidity indicators, and all-cause mortality (phase 2: April 1999 to February 2002), and extended demographic monitoring (January to December 2002). PARTICIPANTS: A total of 130,000 residents of 221 villages in Asembo and Gem were randomized to receive insecticide-treated bednets at the start of phase 1 (111 villages) or phase 2 (110 villages). MAIN OUTCOME MEASURES: Proportion of children younger than 5 years using insecticide-treated bednets, mean number of Anopheles mosquitoes per house, and all-cause mortality rates. RESULTS: Adherence to bednet use in children younger than 5 years increased from 65.9% in phase 1 to 82.5% in phase 2 (P<.001). After 3 to 4 years of bednet use, the mean number of Anopheles mosquitoes per house in the study area was 77% lower than in a neighboring area without bednets (risk ratio, 0.23; 95% confidence interval [CI], 0.15-0.35). All-cause mortality rates in infants aged 1 to 11 months were significantly reduced in intervention villages during phase 1 (hazard ratio [HR], 0.78; 95% CI, 0.67-0.90); low rates were maintained during phase 2. Mortality rates did not differ during 2002 (after up to 6 years of bednet use) between children from former intervention and former control households born during phase 1 (HR, 1.01; 95% CI, 0.86-1.19). CONCLUSIONS: The public health benefits of insecticide-treated bednets were sustained for up to 6 years. There is no evidence that bednet use from birth increases all-cause mortality in older children in an area of intense perennial transmission of malaria.
Animals↗
The effects of varying exposure to malaria transmission on development of antimalarial antibody responses in preschool children. XVI. Asembo Bay Cohort Project.
In areas of intense malaria transmission, malaria morbidity and mortality is highest in children 3-18 months old. Interventions that reduce malaria exposure early in life reduce morbidity but may also delay development of clinical immunity. We assessed the relationship between intensity of malaria exposure and development of antibody responses. Thirty-nine children were monitored monthly, from birth to > or =2.5 years old (1238 observations), and were divided into 3 exposure categories, on the basis of parasitemic episodes or entomological data. Children with low exposure during the first 2 years of life had higher subsequent levels of antibody to merozoite surface protein-1(19-kDa) (a marker of blood-stage responses) by months 24-35 (P<.05). This inverse relationship decreased as children aged. There was no consistent relationship between exposure early in life and subsequent levels of antibody to circumsporozoite protein (a marker of sporozoite-stage responses). These data suggest that, in areas of intense malaria transmission, during the first 3 years of life, interventions that either reduce the number of asexual parasitemic episodes or lower entomological exposure do not delay the development of antibody responses to blood-stage malarial antigens.
Animals↗
Scaling-up coverage with insecticide-treated nets against malaria in Africa: who should pay?
Insecticide-treated nets (ITNs) have been shown to reduce the burden of malaria in African villages by providing personal protection and, if coverage of a community is comprehensive, by reducing the infective mosquito population. We do not accept the view that scaling-up this method should be by making villagers pay for nets and insecticide, with subsidies limited so as not to discourage the private sector. We consider that ITNs should be viewed as a public good, like vaccines, and should be provided via the public sector with generous assistance from donors. Our experience is that teams distributing free ITNs, replacing them after about 4 years when they are torn and retreating them annually, have high productivity and provide more comprehensive and equitable coverage than has been reported for marketing systems. Very few of the free nets are misused or sold. The estimated cost would be an annual expenditure of about US$295 million to provide for all of rural tropical Africa where most of the world's malaria exists. This expenditure is affordable by the world community as a whole, but not by its poorest members. Recently, funding of this order of magnitude has been committed by donor agencies for malaria control.
Africa↗
Sulfadoxine-pyrimethamine in treatment of malaria in Western Kenya: increasing resistance and underdosing.
Between 1993 and 1999, we monitored the efficacy of sulfadoxine-pyrimethamine in 1175 children aged <24 months receiving 2789 treatments for falciparum malaria in western Kenya using a widely deployed age-based dose regimen: infants, 125 plus 6.25 mg (sulfadoxine plus pyrimethamine); children aged 12 to 23 months; 250 plus 12.5 mg. Cumulative treatment failure by day 7, defined as early clinical failure by day 3 or presence of parasitemia on day 7, increased from 18% in 1993 to 1994 to 22% in 1997 to 1998 (P-trend test = 0.20). Based on body weight, the median dose received was 20 plus 1.00 mg/kg, and 73% of the treatments were given at lower than the recommended target dose of 25 plus 1.25 mg/kg. Underdosing accounted for 26% of cumulative treatment failures. After the dose was increased in 1998 (median, 36 plus 1.8 mg/kg), only 4.2% of patients received less than 25 plus 1.25 mg/kg and there was no association with treatment failure. However, the proportion of cumulative treatment failure continued to increase to 27% by 1999 (P-trend test = 0.03). These results raise concern about the longevity of sulfadoxine-pyrimethamine in these settings. Underdosing may have contributed to the rate at which sulfadoxine-pyrimethamine resistance developed in this area. Treatment guidelines should ensure that adequate doses are given from the initial deployment of antimalarials onward.
Anti-Infective Agents↗
Spatial and temporal variation in kinship among Anopheles gambiae (Diptera: Culicidae) mosquitoes.
Genetic relatedness (kinship) among Anopheles gambiae Giles female mosquitoes was assessed using microsatellite loci in five locations across Africa and in nine samples taken between 1994 and 1999 in western Kenya. We assessed variation among samples in kinship as well as the effect of distance on kinship. Relatedness within populations was low, and differences among samples taken at various times from one locale and from different locales were minimal. Mosquitoes collected from the same compound were slightly more closely related than those collected from different compounds. Our results suggest that newly emerged female siblings move relatively short distances into a few nearby compounds for blood feeding, but that they lay eggs in a more distant location. Kinship decreased nonlinearly with increasing distance. The strongest relationship between kinship and distance was observed for mosquitoes collected 0-3 km apart (-0.014/km, P < 0.001). The effect of distance decreased with increasing distance between mosquitoes; at 7 km or more, the kinship/distance slope approached zero and the intercept became negative, suggesting that beyond this range kinship does not decline with distance. This distance may thus represent the upper limit of the diameter of the basic reproductive unit. Nevertheless, the effect of distance on kinship is weak, reflecting extensive dispersal. Because females mate within days after emergence from larval habitats, where the likelihood of mating with a sibling is presumably highest, we propose a slight inbreeding effect.
Animals↗
The efficacy of permethrin-treated bed nets on child mortality and morbidity in western Kenya I. Development of infrastructure and description of study site.
Randomized controlled trials in sub-Saharan Africa have shown that permethrin-treated bed nets and curtains reduce all-cause child mortality by 15-33% in areas with low or high but seasonal malaria transmission. This report describes the study site for a community-based, group-randomized, controlled trial in an area of high and year-round malaria transmission in western Kenya. We outline the development of the human and physical infrastructure required to conduct this trial and discuss some of the difficulties encountered and lessons learned in conducting it.
Bedding and Linens↗
The efficacy of permethrin-treated bed nets on child mortality and morbidity in western Kenya II. Study design and methods.
This paper describes the study design and methods used in a large community-based, group-randomized, controlled trial of permethrin-treated bed nets (ITNs) in an area with intense, perennial malaria transmission in western Kenya conducted between 1996 and 1999. A multi-disciplinary framework was used to explore the efficacy of ITNs in the reduction of all-cause mortality in children less than five years old, the clinical, entomologic, immunologic, and economic impact of ITNs, the social and behavioral determinants of ITN use, and the use of a geographic information system to allow for spatial analyses of these outcomes. Methodologic difficulties encountered in such large-scale field trials are discussed.
Bedding and Linens↗