Malaria in Kenya's western highlands

Abstract

Records from tea estates in the Kericho district in Kenya show that malaria reemerged in the 1980s. Renewed epidemic activity coincided with the emergence of chloroquine-resistant Plasmodium falciparum malaria and may have been triggered by the failure of antimalarial drugs. Meteorologic changes, population movements, degradation of health services, and changes in Anopheles vector populations are possible contributing factors. The highland malaria epidemics of the 1940s were stopped largely by sporontocidal drugs, and combination chemotherapy has recently limited transmission. Antimalarial drugs can limit the pool of gametocytes available to infect mosquitoes during the brief transmission season.

Figure 1

Map of Kenya showing the Nandi and Kericho districts.

Figure 2

Kericho, Kenya, tea plantation in 1998.

Figure 3

Monthly malaria cases on the Kericho tea estates, Kenya, 1942–1952, showing mass administration of proguanil. Data were obtained from Strangeways-Dixon (17) and hospital records.

Figure 4

Monthly malaria incidence at 2 adjacent tea plantations in Kericho, Kenya, 1970–2004. Plantation 1 data are from inpatient admission registers, and plantation 2 data are from weekly malaria slide reports that include outpatients.

Figure 5

Annual malaria inpatient characteristics from tea plantation 1 in Kericho, Kenya, 1970–1999. Percentage of malaria patients compared with percentage of all hospital admissions, percentage of malaria inpatients of highland (>1,500 m) family origin, and ratio of adults to children (<15 years of age) of all malaria inpatients are shown annually as collected from the same admission registers. Gaps indicate missing data.

Figure 6

onthly malaria incidence at 2 adjacent tea plantations in Kericho, Kenya, 1998–2004. Shown are the same data in Figure 4 in an expanded scale. See section on sources of clinical data since 1900 to distinguish outpatient and inpatient composition.

Figure 7

Annual antimalarial drug purchases recorded in the respective tea plantation hospital pharmacy records, Kericho, Kenya, 1997–2002, showing the discontinuation of chloroquine as sulfadoxine-pyrimethamine (SP) became first-line therapy. Records of SP purchases at plantation 1 prior to 2001 were not available.