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Identification of malaria transmission and epidemic hotspots in the western Kenya highlands: its application to malaria epidemic prediction.

Wanjala CL, Waitumbi J, Zhou G, Githeko AK - Parasit Vectors (2011)

Bottom Line: The study was conducted in five sites in the western Kenya highlands, two U-shaped valleys (Iguhu, Emutete), two V-shaped valleys (Marani, Fort-Ternan) and one plateau (Shikondi) for 16 months among 6-15 years old children.The plateau ecosystem has a similar infection and immune response to the V-shaped ecosystems.The U-shaped ecosystems are transmission hotspots.

View Article: PubMed Central - HTML - PubMed

Affiliation: Climate and Human Health Research Unit, Centre for Vector Biology and Control Research, Kenya Medical Research Institute, Kisumu, Kenya. ludwin_kristen@yahoo.com

ABSTRACT

Background: Malaria in the western Kenya highlands is characterized by unstable and high transmission variability which results in epidemics during periods of suitable climatic conditions. The sensitivity of a site to malaria epidemics depends on the level of immunity of the human population. This study examined how terrain in the highlands affects exposure and sensitivity of a site to malaria.

Methods: The study was conducted in five sites in the western Kenya highlands, two U-shaped valleys (Iguhu, Emutete), two V-shaped valleys (Marani, Fort-Ternan) and one plateau (Shikondi) for 16 months among 6-15 years old children. Exposure to malaria was tested using circum-sporozoite protein (CSP) and merozoite surface protein (MSP) immunochromatographic antibody tests; malaria infections were tested by microscopic examination of thick and thin smears, the children's homes were georeferenced using a global positioning system. Paired t-test was used to compare the mean prevalence rates of the sites, K-function was use to determine if the clustering of malaria infections was significant.

Results and discussion: The mean antibody prevalence was 22.6% in Iguhu, 24% in Emutete, 11.5% in Shikondi, 8.3% in Fort-Ternan and 9.3% in Marani. The mean malaria infection prevalence was 23.3% in Iguhu, 21.9% in Emutete, 4.7% in Shikondi, 2.9% in Fort-Ternan and 2.4% in Marani. There was a significant difference in the antibodies and malaria infection prevalence between the two valley systems, and between the two valley systems and the plateau (P < 0.05). There was no significant difference in the antibodies and malaria infection prevalence in the two U-shaped valleys (Iguhu and Emutete) and in the V-shaped valleys (Marani and Fort Ternan) (P > 0.05). There was 8.5- fold and a 2-fold greater parasite and antibody prevalence respectively, in the U-shaped compared to the V-shaped valleys. The plateau antibody and parasite prevalence was similar to that of the V-shaped valleys. There was clustering of malaria antibodies and infections around flat areas in the U-shaped valleys, the infections were randomly distributed in the V-shaped valleys and less clustered at the plateau.

Conclusion: This study showed that the V-shaped ecosystems have very low malaria prevalence and few individuals with an immune response to two major malaria antigens and they can be considered as epidemic hotspots. These populations are at higher risk of severe forms of malaria during hyper-transmission seasons. The plateau ecosystem has a similar infection and immune response to the V-shaped ecosystems. The U-shaped ecosystems are transmission hotspots.

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The prevalence of CSP/MSP antibodies in the five studies, the antibodies prevalence was 2.6 fold higher in the U-shaped valleys (Iguhu and Emutete) than in the V-shaped valleys and the plateau.
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Figure 5: The prevalence of CSP/MSP antibodies in the five studies, the antibodies prevalence was 2.6 fold higher in the U-shaped valleys (Iguhu and Emutete) than in the V-shaped valleys and the plateau.

Mentions: The test kit for antibodies returned a positive result whether the individual responded to one or both antibodies. The mean prevalence of the antibodies in Iguhu was 22.6%, Emutete 24%, Marani 9.3%, Fort Ternan 8.3% and Shikondi 11.5%. There was a significant difference between the antibody prevalence in U-shaped valleys and the V-shaped valleys (p < 0.05, t = -6.226), and between the plateau and U-shaped valleys (p < 0.05, t = -6.182). There was no significant difference in antibody prevalence in the two U-shaped valleys (Iguhu and Emutete) (p > 0.05 t = -0.346), in the two V-shaped valleys (Fort Ternan and Marani) (p > 0.05 t = 0.352) and between the plateau (Shikondi) and the V-shaped valleys (p > 0.05, t = -0.889). An increase in antibody prevalence levels was observed after the rains in September 2009 and these declined rapidly in March 2010 (Figure 5). There was a positive correlation between site-specific mean antibody prevalence rate and mean site-specific malaria parasites prevalence rates, (Adjusted R2 = 0.994; p = 0.00191) (Figure 6a) at the population level but not at the individual level. The mean site-specific prevalence of antibodies increased with the increase in the mean site-specific prevalence of malaria infections in all the study sites during the entire study period (Figure 6b).


Identification of malaria transmission and epidemic hotspots in the western Kenya highlands: its application to malaria epidemic prediction.

Wanjala CL, Waitumbi J, Zhou G, Githeko AK - Parasit Vectors (2011)

The prevalence of CSP/MSP antibodies in the five studies, the antibodies prevalence was 2.6 fold higher in the U-shaped valleys (Iguhu and Emutete) than in the V-shaped valleys and the plateau.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3117811&req=5

Figure 5: The prevalence of CSP/MSP antibodies in the five studies, the antibodies prevalence was 2.6 fold higher in the U-shaped valleys (Iguhu and Emutete) than in the V-shaped valleys and the plateau.
Mentions: The test kit for antibodies returned a positive result whether the individual responded to one or both antibodies. The mean prevalence of the antibodies in Iguhu was 22.6%, Emutete 24%, Marani 9.3%, Fort Ternan 8.3% and Shikondi 11.5%. There was a significant difference between the antibody prevalence in U-shaped valleys and the V-shaped valleys (p < 0.05, t = -6.226), and between the plateau and U-shaped valleys (p < 0.05, t = -6.182). There was no significant difference in antibody prevalence in the two U-shaped valleys (Iguhu and Emutete) (p > 0.05 t = -0.346), in the two V-shaped valleys (Fort Ternan and Marani) (p > 0.05 t = 0.352) and between the plateau (Shikondi) and the V-shaped valleys (p > 0.05, t = -0.889). An increase in antibody prevalence levels was observed after the rains in September 2009 and these declined rapidly in March 2010 (Figure 5). There was a positive correlation between site-specific mean antibody prevalence rate and mean site-specific malaria parasites prevalence rates, (Adjusted R2 = 0.994; p = 0.00191) (Figure 6a) at the population level but not at the individual level. The mean site-specific prevalence of antibodies increased with the increase in the mean site-specific prevalence of malaria infections in all the study sites during the entire study period (Figure 6b).

Bottom Line: The study was conducted in five sites in the western Kenya highlands, two U-shaped valleys (Iguhu, Emutete), two V-shaped valleys (Marani, Fort-Ternan) and one plateau (Shikondi) for 16 months among 6-15 years old children.The plateau ecosystem has a similar infection and immune response to the V-shaped ecosystems.The U-shaped ecosystems are transmission hotspots.

View Article: PubMed Central - HTML - PubMed

Affiliation: Climate and Human Health Research Unit, Centre for Vector Biology and Control Research, Kenya Medical Research Institute, Kisumu, Kenya. ludwin_kristen@yahoo.com

ABSTRACT

Background: Malaria in the western Kenya highlands is characterized by unstable and high transmission variability which results in epidemics during periods of suitable climatic conditions. The sensitivity of a site to malaria epidemics depends on the level of immunity of the human population. This study examined how terrain in the highlands affects exposure and sensitivity of a site to malaria.

Methods: The study was conducted in five sites in the western Kenya highlands, two U-shaped valleys (Iguhu, Emutete), two V-shaped valleys (Marani, Fort-Ternan) and one plateau (Shikondi) for 16 months among 6-15 years old children. Exposure to malaria was tested using circum-sporozoite protein (CSP) and merozoite surface protein (MSP) immunochromatographic antibody tests; malaria infections were tested by microscopic examination of thick and thin smears, the children's homes were georeferenced using a global positioning system. Paired t-test was used to compare the mean prevalence rates of the sites, K-function was use to determine if the clustering of malaria infections was significant.

Results and discussion: The mean antibody prevalence was 22.6% in Iguhu, 24% in Emutete, 11.5% in Shikondi, 8.3% in Fort-Ternan and 9.3% in Marani. The mean malaria infection prevalence was 23.3% in Iguhu, 21.9% in Emutete, 4.7% in Shikondi, 2.9% in Fort-Ternan and 2.4% in Marani. There was a significant difference in the antibodies and malaria infection prevalence between the two valley systems, and between the two valley systems and the plateau (P < 0.05). There was no significant difference in the antibodies and malaria infection prevalence in the two U-shaped valleys (Iguhu and Emutete) and in the V-shaped valleys (Marani and Fort Ternan) (P > 0.05). There was 8.5- fold and a 2-fold greater parasite and antibody prevalence respectively, in the U-shaped compared to the V-shaped valleys. The plateau antibody and parasite prevalence was similar to that of the V-shaped valleys. There was clustering of malaria antibodies and infections around flat areas in the U-shaped valleys, the infections were randomly distributed in the V-shaped valleys and less clustered at the plateau.

Conclusion: This study showed that the V-shaped ecosystems have very low malaria prevalence and few individuals with an immune response to two major malaria antigens and they can be considered as epidemic hotspots. These populations are at higher risk of severe forms of malaria during hyper-transmission seasons. The plateau ecosystem has a similar infection and immune response to the V-shaped ecosystems. The U-shaped ecosystems are transmission hotspots.

Show MeSH
Related in: MedlinePlus