Clinical malaria case definition and malaria attributable fraction in the highlands of western Kenya.

BackgroundIn African highland areas where endemicity of malaria varies greatly according to altitude and topography, parasitaemia accompanied by fever may not be sufficient to define an episode of clinical malaria in endemic areas. To evaluate the effectiveness of malaria interventions, age-specific case definitions of clinical malaria needs to be determined. Cases of clinical malaria through active case surveillance were quantified in a highland area in Kenya and defined clinical malaria for different age groups.MethodsA cohort of over 1,800 participants from all age groups was selected randomly from over 350 houses in 10 villages stratified by topography and followed for two-and-a-half years. Participants were visited every two weeks and screened for clinical malaria, defined as an individual with malaria-related symptoms (fever [axillary temperature≥37.5°C], chills, severe malaise, headache or vomiting) at the time of examination or 1-2 days prior to the examination in the presence of a Plasmodium falciparum positive blood smear. Individuals in the same cohort were screened for asymptomatic malaria infection during the low and high malaria transmission seasons. Parasite densities and temperature were used to define clinical malaria by age in the population. The proportion of fevers attributable to malaria was calculated using logistic regression models.ResultsIncidence of clinical malaria was highest in valley bottom population (5.0% cases per 1,000 population per year) compared to mid-hill (2.2% cases per 1,000 population per year) and up-hill (1.1% cases per 1,000 population per year) populations. The optimum cut-off parasite densities through the determination of the sensitivity and specificity showed that in children less than five years of age, 500 parasites per μl of blood could be used to define the malaria attributable fever cases for this age group. In children between the ages of 5-14, a parasite density of 1,000 parasites per μl of blood could be used to define the malaria attributable fever cases. For individuals older than 14 years, the cut-off parasite density was 3,000 parasites per μl of blood.ConclusionClinical malaria case definitions are affected by age and endemicity, which needs to be taken into consideration during evaluation of interventions

Community-wide benefits of targeted indoor residual spray for malaria control in the Western Kenya Highland

<p>Abstract</p> <p>Background</p> <p>Interest in indoor residual spray (IRS) has been rekindled in recent years, as it is increasingly considered to be a key component of integrated malaria management. Regular spraying of each human dwelling becomes less and less practical as the control area increases. Where malaria transmission is concentrated around focal points, however, targeted IRS may pose a feasible alternative to mass spraying. Here, the impact of targeted IRS was assessed in the highlands of western Kenya.</p> <p>Methods</p> <p>Indoor residual spray using lambda-cyhalothrin insecticide was carried out during the last week of April 2005 in 1,100 targeted houses, located in the valley bottom areas of Iguhu village, Kakamega district of western Kenya. Although the uphill areas are more densely populated, valleys are believed to be malaria transmission hotspots. The aim of the study was to measurably reduce the vector density and malaria transmission in uphill areas by focusing control on these hotspots. A cohort of 1,058 children from 1-5 yrs of age was randomly selected from a 4 km by 6 km study area for the baseline malaria prevalence survey after pre-clearing malaria infections during the third week of April 2005, and the prevalence of <it>Plasmodium </it>infections was tested bi-weekly. Seasonal changes in mosquito densities 12 months before the IRS and 12 months after the IRS was monitored quarterly based on 300 randomly selected houses. Monthly parasitological surveys were also carried out in the same area with 129-661 randomly selected school children of age 6-13 yrs.</p> <p>Results</p> <p>The result of monthly parasitological surveys indicated that malaria prevalence in school children was reduced by 64.4% in the intervention valley area and by 46.3% in the intervention uphill area after 12 months of follow-ups in contrast to nonintervention areas (valley or uphill). The cohort study showed an average of 4.5% fewer new infections biweekly in the intervention valley compare to nonintervention valley and the relative reduction in incidence rate by week 14 was 65.4%. The relative reduction in incidence rate in intervention uphill by week 14 was 46.4%. <it>Anopheles gambiae </it>densities were reduced by 96.8% and 51.6% in the intervention valley and intervention uphill, respectively, and <it>Anopheles funestus </it>densities were reduced by 85.3% and 69.2% in the intervention valley and intervention uphill, respectively.</p> <p>Conclusion</p> <p>Vector control had significant indirect impact on the densely populated uphill areas when IRS was targeted to the high-risk valleys. Additionally, the wide-reaching benefits of IRS in reducing vector prevalence and disease incidence was observed for at least six months following spraying, suggesting targeted IRS as an effective tool in malaria control.</p

Plasmodium falciparum Spatial Analysis, Western Kenya Highlands

Parasite transmission is intense in the highlands, and these areas are vulnerable to epidemics

Efficacy of Aquatain, a Monomolecular Film, for the Control of Malaria Vectors in Rice Paddies

Background Rice paddies harbour a large variety of organisms including larvae of malaria mosquitoes. These paddies are challenging for mosquito control because their large size, slurry and vegetation make it difficult to effectively apply a control agent. Aquatain, a monomolecular surface film, can be considered a suitable mosquito control agent for such breeding habitats due to its physical properties. The properties allow Aquatain to self-spread over a water surface and affect multiple stages of the mosquito life cycle. Methodology/Principal Findings A trial based on a pre-test/post-test control group design evaluated the potential of Aquatain as a mosquito control agent at Ahero rice irrigation scheme in Kenya. After Aquatain application at a dose of 2 ml/m2 on rice paddies, early stage anopheline larvae were reduced by 36%, and late stage anopheline larvae by 16%. However, even at a lower dose of 1 ml/m2 there was a 93.2% reduction in emergence of anopheline adults and 69.5% reduction in emergence of culicine adults. No pupation was observed in treated buckets that were part of a field bio-assay carried out parallel to the trial. Aquatain application saved nearly 1.7 L of water in six days from a water surface of 0.2 m2 under field conditions. Aquatain had no negative effect on rice plants as well as on a variety of non-target organisms, except backswimmers. Conclusions/Significance We demonstrated that Aquatain is an effective agent for the control of anopheline and culicine mosquitoes in irrigated rice paddies. The agent reduced densities of aquatic larval stages and, more importantly, strongly impacted the emergence of adult mosquitoes. Aquatain also reduced water loss due to evaporation. No negative impacts were found on either abundance of non-target organisms, or growth and development of rice plants. Aquatain, therefore, appears a suitable mosquito control tool for use in rice agro-ecosystems

New records of Anopheles arabiensis breeding on the Mount Kenya highlands indicate indigenous malaria transmission

BACKGROUND: Malaria cases on the highlands west of Mount Kenya have been noticed since 10 – 20 years ago. It was not clear whether these cases were introduced from the nearby lowland or resulted from local transmission because of no record of vector mosquitoes on the highlands. Determination of presence and abundance of malaria vector is vital for effective control and epidemic risk assessment of malaria among both local residents and tourists. METHODS: A survey on 31 aquatic sites for the malaria-vector mosquitoes was carried out along the primary road on the highlands around Mount Kenya and the nearby Mwea lowland during April 13 to June 28, 2005. Anopheline larvae were collected and reared into adults for morphological and molecular species identification. In addition, 31 families at three locations of the highlands were surveyed using a questionnaire about their history of malaria cases during the past five to 20 years. RESULTS: Specimens of Anopheles arabiensis were molecularly identified in Karatina and Naro Moru on the highlands at elevations of 1,720 – 1,921 m above sea level. This species was also the only malaria vector found in the Mwea lowland. Malaria cases were recorded in the two highland locations in the past 10 years with a trend of increasing. CONCLUSION: Local malaria transmission on the Mount Kenya highlands is possible due to the presence of An. arabiensis. Land use pattern and land cover might be the key factors affecting the vector population dynamics and the highland malaria transmission in the region

Epidemiological risk factors for clinical malaria infection in the highlands of Western Kenya.

BackgroundUnderstanding the complex heterogeneity of risk factors that can contribute to an increased risk of malaria at the individual and household level will enable more effective use of control measures. The objective of this study was to understand individual and household factors that influence clinical malaria infection among individuals in the highlands of Western Kenya.MethodsThis was a matched case-control study undertaken in the Western Kenya highlands. Clinical malaria cases were recruited from health facilities and matched to asymptomatic individuals from the community who served as controls. Each participant was screened for malaria using microscopy. Follow-up surveys were conducted with individual households to collect socio-economic data. The houses were also checked using pyrethrum spray catches to collect mosquitoes.ResultsA total of 302 malaria cases were matched to 604 controls during the surveillance period. Mosquito densities were similar in the houses of both groups. A greater percentage of people in the control group (64.6%) used insecticide-treated bed nets (ITNs) compared to the families of malaria cases (48.3%). Use of ITNs was associated with lower level of clinical malaria episodes (odds ratio 0.51; 95% CI 0.39-0.68; P &lt; 0.0001). Low income was the most important factor associated with higher malaria infections (adj. OR 4.70). Use of malaria prophylaxis was the most important factor associated with less malaria infections (adj OR 0.36). Mother's (not fathers) employment status (adj OR 0.48) and education level (adj OR 0.54) was important malaria risk factor. Houses with open eaves was an important malaria risk factor (adj OR 1.72).ConclusionThe identification of risk factors for clinical malaria infection provides information on the local malaria epidemiology and has the potential to lead to a more effective and targeted use of malaria control measures. These risk factors could be used to assess why some individuals acquire clinical malaria whilst others do not and to inform how intervention could be scaled at the local level