Abstract:Background: Recent resurgence of malaria in the highlands of Western Kenya has called for a more comprehensive understanding of the previously neglected complex highland vector ecology. Besides other drivers of malaria epidemiology, topography is likely to have a major effect on spatial vector and parasite distribution. The aim of this study was to determine the effects of topography on malaria spatial vector distribution and parasite prevalence.
“…Three holo-endemic sites were located in lowlands: Kombewa (34°30′E, 0°07′N, 1,150–1,300 m asl); Miwani (0°07′S, 35°05′E, 1,100–1,200 m asl); and Rae (00°25′S 34°95′E, 1,143–1,200 m asl) in Kisumu County (Figure 1). Iguhu and Emakakha have flat shaped valleys, Kombewa, Rae and Miwani are in the flat lowland regions, while Marani has steep valleys [11]. Climate in western Kenya consists mainly of two seasons of rainfall, a long rainy season that is the peak of malaria transmission between March and May and a short one between October and November.Figure 1Map showing the study sites in the western Kenya highlands.…”
BackgroundMalaria is a great public health burden and Africa suffers the largest share of malaria-attributed deaths. Despite control efforts targeting indoor malaria transmission, such as insecticide-treated bed nets (ITNs) and deployment of indoor residual spraying, transmission of the parasite in western Kenya is still maintained. This study was carried out to determine the impact of ITNs on indoor vector densities and biting behaviour in western Kenya.MethodsIndoor collection of adult mosquitoes was done monthly in six study sites in western Kenya using pyrethrum spray collections from 2012 to 2014. The rotator trap collections were done in July–August in 2013 and May–June in 2014. Mosquitoes were collected every 2 h between 18.00 and 08.00 h. Human behaviour study was conducted via questionnaire surveys. Species within Anopheles gambiae complex was differentiated by PCR and sporozoite infectivity was determined by ELISA. Species distribution was determined and bed net coverage in the study sites was recorded.ResultsDuring the study a total of 5,469 mosquito vectors were collected from both PSC and Rotator traps comprising 3,181 (58.2%) Anopheles gambiae and 2,288 (41.8%) Anopheles funestus. Compared to all the study sites, Rae had the highest density of An. gambiae with a mean of 1.2 (P < 0.001) while Kombewa had the highest density of An. funestus with a mean of 1.08 (P < 0.001). Marani had the lowest density of vectors with 0.06 An. gambiae and 0.17 An. funestus (P < 0.001). Among the 700 PCR confirmed An. gambiaes.l. individuals, An. gambiaes.s. accounted for 49% and An. arabiensis 51%. Over 50% of the study population stayed outdoors between 18.00 and 20.00 and 06.00 and 08.00 which was the time when highest densities of blood fed vectors were collected. Anopheles gambies.s. was the main malaria parasite vector in the highland sites and An. arabiensis in the lowland sites. Bed net ownership in 2012 averaged 87% across the study sites.ConclusionsThis study suggests that mass distribution of ITNs has had a significant impact on vector densities, species distribution and sporozoite rate. However, shift of biting time poses significant threats to the current malaria vector control strategies which heavily rely on indoor controls.
“…Three holo-endemic sites were located in lowlands: Kombewa (34°30′E, 0°07′N, 1,150–1,300 m asl); Miwani (0°07′S, 35°05′E, 1,100–1,200 m asl); and Rae (00°25′S 34°95′E, 1,143–1,200 m asl) in Kisumu County (Figure 1). Iguhu and Emakakha have flat shaped valleys, Kombewa, Rae and Miwani are in the flat lowland regions, while Marani has steep valleys [11]. Climate in western Kenya consists mainly of two seasons of rainfall, a long rainy season that is the peak of malaria transmission between March and May and a short one between October and November.Figure 1Map showing the study sites in the western Kenya highlands.…”
BackgroundMalaria is a great public health burden and Africa suffers the largest share of malaria-attributed deaths. Despite control efforts targeting indoor malaria transmission, such as insecticide-treated bed nets (ITNs) and deployment of indoor residual spraying, transmission of the parasite in western Kenya is still maintained. This study was carried out to determine the impact of ITNs on indoor vector densities and biting behaviour in western Kenya.MethodsIndoor collection of adult mosquitoes was done monthly in six study sites in western Kenya using pyrethrum spray collections from 2012 to 2014. The rotator trap collections were done in July–August in 2013 and May–June in 2014. Mosquitoes were collected every 2 h between 18.00 and 08.00 h. Human behaviour study was conducted via questionnaire surveys. Species within Anopheles gambiae complex was differentiated by PCR and sporozoite infectivity was determined by ELISA. Species distribution was determined and bed net coverage in the study sites was recorded.ResultsDuring the study a total of 5,469 mosquito vectors were collected from both PSC and Rotator traps comprising 3,181 (58.2%) Anopheles gambiae and 2,288 (41.8%) Anopheles funestus. Compared to all the study sites, Rae had the highest density of An. gambiae with a mean of 1.2 (P < 0.001) while Kombewa had the highest density of An. funestus with a mean of 1.08 (P < 0.001). Marani had the lowest density of vectors with 0.06 An. gambiae and 0.17 An. funestus (P < 0.001). Among the 700 PCR confirmed An. gambiaes.l. individuals, An. gambiaes.s. accounted for 49% and An. arabiensis 51%. Over 50% of the study population stayed outdoors between 18.00 and 20.00 and 06.00 and 08.00 which was the time when highest densities of blood fed vectors were collected. Anopheles gambies.s. was the main malaria parasite vector in the highland sites and An. arabiensis in the lowland sites. Bed net ownership in 2012 averaged 87% across the study sites.ConclusionsThis study suggests that mass distribution of ITNs has had a significant impact on vector densities, species distribution and sporozoite rate. However, shift of biting time poses significant threats to the current malaria vector control strategies which heavily rely on indoor controls.
“…In the western Kenya highlands, anopheline larval habitats are generally restricted to the valley bottoms, especially during the dry season (Minakawa et al, 2005b;Mushinzimana et al, 2006;Githeko et al, 2012). Githeko et al (2006) classified study villages as 'valley-bottom', 'mid-hill' and 'hill-top' and found that vector density, EIR and malaria prevalence all decreased upslope. Similarly, Brooker et al (2004) and Kazembe (2007) found that altitude is a significant risk factor for malaria.…”
“…McWilliams et al (2007) used an adaptive Table 3 Potential impacts of climate change at a regional level (based on Githeko et al 2006) Place Potential effect…”
Section: Balancing the Environment And Human Health Issues: Adaptive mentioning
This review brings together information on mosquitoes, the diseases they transmit and the wetlands that provide habitats for the immature stages (eggs and larvae). Wetland values are mentioned, though the main literature on this does not generally overlap the mosquito issue. Mosquito management is overviewed to include: the use of larvicides, source reduction in intertidal wetlands and management in freshwater systems. There is not a great deal of information on mosquitoes and freshwater systems, except for constructed wetlands and they are considered separately. We then consider restoration mainly in the context of wetlands that have been the subject of habitat modification for mosquito control. Land use and climate change, as they affect mosquitoes and the diseases they transmit, are also reviewed, as this will affect wetlands via management activities. Finally the review addresses the critical issue of balancing health, both human and environmental, in an adaptive framework. It concludes that there is a need to ensure that both mosquito and wetland management communicate and integrate to sustain wetland and human health.
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