Changing Patterns of Malaria Epidemiology between 2002 and 2010 in Western Kenya: The Fall and Rise of Malaria

Abstract

BackgroundThe impact of insecticide treated nets (ITNs) on reducing malaria incidence is shown mainly through data collection from health facilities. Routine evaluation of long-term epidemiological and entomological dynamics is currently unavailable. In Kenya, new policies supporting the provision of free ITNs were implemented nationwide in June 2006. To evaluate the impacts of ITNs on malaria transmission, we conducted monthly surveys in three sentinel sites with different transmission intensities in western Kenya from 2002 to 2010.Methods and FindingsLongitudinal samplings of malaria parasite prevalence in asymptomatic school children and vector abundance in randomly selected houses were undertaken monthly from February 2002. ITN ownership and usage surveys were conducted annually from 2004 to 2010. Asymptomatic malaria parasite prevalence and vector abundances gradually decreased in all three sites from 2002 to 2006, and parasite prevalence reached its lowest level from late 2006 to early 2007. The abundance of the major malaria vectors, Anopheles funestus and An. gambiae, increased about 5–10 folds in all study sites after 2007. However, the resurgence of vectors was highly variable between sites and species. By 2010, asymptomatic parasite prevalence in Kombewa had resurged to levels recorded in 2004/2005, but the resurgence was smaller in magnitude in the other sites. Household ITN ownership was at 50–70% in 2009, but the functional and effective bed net coverage in the population was estimated at 40.3%, 49.4% and 28.2% in 2010 in Iguhu, Kombewa, and Marani, respectively.ConclusionThe resurgence in parasite prevalence and malaria vectors has been observed in two out of three sentinel sites in western Kenya despite a high ownership of ITNs. The likely factors contributing to malaria resurgence include reduced efficacy of ITNs, insecticide resistance in mosquitoes and lack of proper use of ITNs. These factors should be targeted to avoid further resurgence of malaria transmission.

Monocyte dysregulation and systemic inflammation during pediatric falciparum malaria

“…The study was conducted in an area of western Kenya where transmission of P. falciparum and child malaria morbidity are increasing, despite the widespread distribution of long-lasting insecticidal nets (30,31). Demographic features and pertinent clinical laboratory results for children with acute uncomplicated malaria, their samples obtained 6 weeks after treatment (6-week recovery samples), and healthy asymptomatic children and adults from the same communities where malaria cases were recruited are presented in Supplemental Table 1 (supplemental material available online with this article; https://doi.org/10.1172/jci.insight.95352DS1).…”

Factors Associated with Sustained Use of Long-Lasting Insecticide-Treated Nets Following a Reduction in Malaria Transmission in Southern Zambia

“…Nets will be discarded or used for other activities more commonly in areas where perceived risk is low. 8,17 These findings suggest that if malaria transmission is reduced, personal protective measures such as LLINs may no longer be used. That LLIN ownership and use were higher in longitudinal households suggest that repeated messaging may be useful to ensure sustained use.…”

“…2 Unfortunately, these gains may be followed by resurgence of malaria in regions with high transmission potential if control efforts are not sustained. [3][4][5][6][7][8][9] As transmission and perceived risk decline, LLIN access and use need to be maintained.…”

Molecular Characterization Reveals Diverse and Unknown Malaria Vectors in the Western Kenyan Highlands

“…funestus complexes. [28][29][30][31][32][33] There are no reports of other anophelines in the area acting as major vectors and only limited descriptive vector studies from the highlands of Rachuonyo South, Nyanza Province. The western Kenyan highlands is an area of unstable, sometimes epidemic malaria 34 where anopheline vector dynamics determine the spread and maintenance of malaria transmission.…”