Malaria in Kenya's Western Highlands

Shanks, G. Dennis; Hay, Simon I.; Omumbo, Judith A.; Snow, Robert W.

doi:10.3201/eid1109.041131

Cited by 75 publications

(101 citation statements)

References 31 publications

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“…half of those at AHP). Furthermore, more effective antimalarials were introduced at BBK after 1999; this seemed to keep the number of cases consistently lower than that at AHP in the following years (Shanks et al 2005b). The lower incidence at BBK could mask a regime shift in the 1980s and when coupled to the overall decrease of cases in recent years may explain the lack of detection of long-term change in transmission.…”

Section: Discussionmentioning

confidence: 99%

“…The model itself cannot specify any given mechanism per se. One possibility is the known increase in drug resistance (Malakooti et al 1998;Shanks et al 2005b). Another possibility is an increase in the transmission rate due to environmental change, including higher temperatures (Pascual et al 2006) and change in mosquito life history mediated by land-use and agricultural practices ( Wilson et al 1990;Lyimo & Koella 1992;Lindblade et al 2000;Koenraadt et al 2004;Mutero et al 2004;Kebede et al 2005).…”

Section: Discussionmentioning

confidence: 99%

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Shifting patterns: malaria dynamics and rainfall variability in an African highland

et al. 2007

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The long-term patterns of malaria in the East African highlands typically involve not only a general upward trend in cases but also a dramatic increase in the size of epidemic outbreaks. The role of climate variability in driving epidemic cycles at interannual time scales remains controversial, in part because it has been seen as conflicting with the alternative explanation of purely endogenous cycles exclusively generated by the nonlinear dynamics of the disease. We analyse a long temporal record of monthly cases from 1970 to 2003 in a highland of western Kenya with both a time-series epidemiological model (time-series susceptibleinfected-recovered) and a statistical approach specifically developed for non-stationary patterns. Results show that multiyear cycles of malaria outbreaks appear in the 1980s, concomitant with the timing of a regime shift in the dynamics of cases; the cycles become more pronounced in the 1990s, when the coupling between disease and rainfall is also stronger as the variance of rainfall increased at the frequencies of coupling. Disease dynamics and climate forcing play complementary and interacting roles at different temporal scales. Thus, these mechanisms should not be viewed as alternative and their interaction needs to be integrated in the development of future predictive models.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Shifting patterns: malaria dynamics and rainfall variability in an African highland

et al. 2007

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“…It is interesting to consider the pattern of warming described here and in particular the The beginning of the 1980s coincides also with the development of chloroquine resistance against P. falciparum in this part of Africa (5,32). Unsuccessful treatment has been proposed as a major factor behind the observed changes in malaria in the past decades (5).…”

Section: Discussionmentioning

confidence: 99%

Malaria resurgence in the East African highlands: Temperature trends revisited

Pascual

Ahumada

Chaves

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

371

296

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The incidence of malaria in the East African highlands has increased since the end of the 1970s. The role of climate change in the exacerbation of the disease has been controversial, and the specific influence of rising temperature (warming) has been highly debated following a previous study reporting no evidence to support a trend in temperature. We revisit this result using the same temperature data, now updated to the present from 1950 to 2002 for four high-altitude sites in East Africa where malaria has become a serious public health problem. With both nonparametric and parametric statistical analyses, we find evidence for a significant warming trend at all sites. To assess the biological significance of this trend, we drive a dynamical model for the population dynamics of the mosquito vector with the temperature time series and the corresponding detrended versions. This approach suggests that the observed temperature changes would be significantly amplified by the mosquito population dynamics with a difference in the biological response at least 1 order of magnitude larger than that in the environmental variable. Our results emphasize the importance of considering not just the statistical significance of climate trends but also their biological implications with dynamical models.amplification of temperature increase ͉ climate change ͉ vector-transmitted disease ͉ mosquito population dynamics

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“…1). In western Kenya, particularly the basin region of Lake Victoria, malaria transmission is perennial, and transmission intensity measured by entomological inoculation rate (EIR) is typically in the order of several dozens to several hundreds infectious bites per person per year, and Anopheles gambiae is the predominant malaria vector (Chen et al 2004, Shanks et al 2005. Malaria transmission in the Great Rift Valley is seasonal, An.…”

Section: Study Areas and Specimen Collectionmentioning

confidence: 99%

“…Inexpensive insecticides such as DDT and dieldrin, used for indoor residual spray during the global malaria eradication campaign in the 1950s and 1960s, were initially very effective in many countries, including Kenya (Shanks et al 2005). However, the effectiveness of DDT and dieldrin was not sustained, partially because of the emergence of resistance to the insecticides in the mosquito vectors (Akogbeto et al 2006).…”

Section: Introductionmentioning

confidence: 99%

Monooxygenase Levels and Knockdown Resistance (kdr) Allele Frequencies in Anopheles gambiae and Anopheles arabiensis in Kenya

Chen

Githeko

Githure

et al. 2008

Journal of Medical Entomology

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Pyrethroid-treated bed nets and indoor spray are important components of malaria control strategies in Kenya. Information on resistance to pyrethroid insecticides in Anopheles gambiae and An. arabiensis populations is essential to the selection of appropriate insecticides and the management of insecticide resistance. Monooxygenase activity and knockdown resistance (kdr) allele frequency are biochemical and molecular indicators of mosquito resistance to pyrethroids. This study determined baseline information on monooxygenase activity and kdr allele frequency in anopheline mosquitoes in the western region, the Great Rift Valley-central province region, and the coastal region of Kenya. A total of 1990 field-collected individuals, representing 12 An. gambiae and 22 An. arabiensis populations was analyzed. We found significant among-population variation in monooxygenase activity in An. gambiae and An. arabiensis and substantial variability among individuals within populations. Nine out of 12 An. gambiae populations exhibited significantly higher average monooxygenase activity than the susceptible Kisumu reference strain. The kdr alleles (L1014S) were detected in three An. gambiae populations, and one An. arabiensis population in western Kenya, but not in the Rift Valley-central region and the coastal Kenya region. All genotypes with the kdr alleles were heterozygous, and the conservative estimation of kdr allele frequency was below 1% in these four populations. Information on monooxygenase activity and kdr allele frequency reported in this study provided baseline data for monitoring insecticide resistance changes in Kenya during the era when large-scale insecticide-treated bednet and indoor residual spray campaigns were being implemented.

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Malaria in Kenya's Western Highlands

Abstract: Reemergence of epidemics in tea plantations will likely result in antimalarial-drug resistance.

Cited by 75 publications

References 31 publications

Shifting patterns: malaria dynamics and rainfall variability in an African highland

Shifting patterns: malaria dynamics and rainfall variability in an African highland

Malaria resurgence in the East African highlands: Temperature trends revisited

Monooxygenase Levels and Knockdown Resistance (kdr) Allele Frequencies in Anopheles gambiae and Anopheles arabiensis in Kenya

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