Impact of insecticide-treated bed nets on malaria transmission indices on the south coast of Kenya

Abstract

BackgroundBesides significantly reducing malaria vector densities, prolonged usage of bed nets has been linked to decline of Anopheles gambiae s.s. relative to Anopheles arabiensis, changes in host feeding preference of malaria vectors, and behavioural shifts to exophagy (outdoor biting) for the two important malaria vectors in Africa, An. gambiae s.l. and Anopheles funestus. In southern coastal Kenya, bed net use was negligible in 1997-1998 when Anopheles funestus and An. gambiae s.s. were the primary malaria vectors, with An. arabiensis and Anopheles merus playing a secondary role. Since 2001, bed net use has increased progressively and reached high levels by 2009-2010 with corresponding decline in malaria transmission.MethodsTo evaluate the impact of the substantial increase in household bed net use within this area on vector density, vector composition, and human-vector contact, indoor and outdoor resting mosquitoes were collected in the same region during 2009-2010 using pyrethrum spray catches and clay pots for indoor and outdoor collections respectively. Information on bed net use per sleeping spaces and factors influencing mosquito density were determined in the same houses using Poisson regression analysis. Species distribution was determined, and number of mosquitoes per house, human-biting rates (HBR), and entomological inoculation rate (EIR) were compared to those reported for the same area during 1997-1998, when bed net coverage had been minimal.ResultsCompared to 1997-1998, a significant decline in the relative proportion of An. gambiae s.s. among collected mosquitoes was noted, coupled with a proportionate increase of An. arabiensis. Following > 5 years of 60-86% coverage with bed nets, the density, human biting rate and EIR of indoor resting mosquitoes were reduced by more than 92% for An. funestus and by 75% for An. gambiae s.l. In addition, the host feeding choice of both vectors shifted more toward non-human vertebrates. Besides bed net use, malaria vector abundance was also influenced by type of house construction and according to whether one sleeps on a bed or a mat (both of these are associated with household wealth). Mosquito density was positively associated with presence of domestic animals.ConclusionsThese entomological indices indicate a much reduced human biting rate and a diminishing role of An. gambiae s.s. in malaria transmission following high bed net coverage. While increasing bed net coverage beyond the current levels may not significantly reduce the transmission potential of An. arabiensis, it is anticipated that increasing or at least sustaining high bed net coverage will result in a diminished role for An. funestus in malaria transmission.

Marked Decline in Malaria Prevalence among Pregnant Women and Their Offspring from 1996 to 2010 on the South Kenyan Coast

“…25,26 Importantly, these changes led to a marked reduction in the incidence of malaria infection in This result also corresponded to a 99% decline in the entomological inoculation rate over approximately the same span of time in the same area, emphasizing that these control measures are likely responsible for the observed changes. 20 There were limitations to the present study. Children were followed approximately every 6 months, and it is likely that intervening infections occurred, resulting in an underestimation of the incidence of malaria infections.…”

“…3,5 Malaria vector populations have also markedly declined. 19,20 The increasing use of ITNs and greater availability of effective antimalarial medications have been thought to be major contributors to this marked decrease in malaria in coastal regions of East Africa, although a direct association with these interventions and reduction in malaria transmission has not been firmly established. Indeed, the decline in malaria vector populations and hospital admissions preceded widespread use of bed nets and drug distribution, suggesting that other factors, such as changes in local ecology, economic development, and better use of health facilities, have contributed to these declines.…”

Impact of Polyparasitic Infections on Anemia and Undernutrition among Kenyan Children Living in a Schistosoma haematobium-Endemic Area

“…We had previously found no predictable seasonal pattern in 2009-2010 malaria transmission based on monthly or quarterly rainfall. 38 Other location-specific climatic variations are expected to be reflected embedded in the village-level factors included in the analysis.…”

“…38 Anemia has been acknowledged as a major public health threat, 27 with multiple measurable downstream effects on physical and cognitive function in children as well as risk for low-birth weight pregnancies and increased prematurity. Iron deficiency is typically considered the most common etiology of acquired anemia.…”

Suhu, Kelembaban Dan Penggunaan Kelambu Berkaitan Dengan Tingginya Kejadian Malaria Di Desa Durian Luncuk

“…Hal ini sejalan dengan penelitian yang di lakukan oleh Nasir (2013) dan Mutuku et al (2011) yang menyatakan bahwa ada hubungan yang bermakna penggunaan kelambu dengan kejadian penyakit malaria. Hasil penelitian juga menunjukkan bahwa…”