Longitudinal cohort study of the epidemiology of malaria infections in an area of intense malaria transmission I. Description of study site, general methodology, and study population.

Abstract

Abstract. A large-scale longitudinal cohort project was initiated in western Kenya in June 1992. The primary purpose of the project was to study Plasmodium falciparum malaria in a highly endemic area using a comprehensive and multidisciplinary approach, which included epidemiology, entomology, and immunology. Between June 1992 and July 1994, pregnant women living in 15 rural villages were identified during a monthly census and 1,164 were enrolled. The women were followed-up throughout their pregnancy and they, along with their newborn infants and direct siblings of the infants' less than 15 years of age, were monitored over time. As of May 1995, 1,017 infants had been born to these women. This paper presents the design and general methodology used in this study and describes the initial experience with intense monitoring of a large population over a prolonged period.Plasmodium falciparum infection can present with a wide spectrum of signs, symptoms, and history, from a fatal disease to an apparently asymptomatic infection, from a rapidly progressing, fulminant illness to a chronic insult. Many of the reasons for this wide variation in the presentation of this disease have been known for years, such as the protection afforded by some hemoglobinopathies.1,2 Recent scientific advancements and closer coordination of work done in various disciplines have begun to explain other observations for which there previously has been no satisfying explanation. For instance, application of newer genetic techniques to large populations has linked a particular human leukocyte antigen (HLA) type to increased risk of cerebral malaria, 3 partly explaining the observation that there are some people who develop cerebral malaria while most of their neighbors, with presumably the same exposures and histories, do not. 4 Combining the work of entomologists with that of clinical epidemiologists has demonstrated an effect of exposure pressure on disease development. 5 Because of the growing realization of complex interrelationships among the parasite, vector, environment, and host, advancing our understanding of falciparum malaria will require investigation of most if not all of these factors simultaneously. Conducting studies with similar designs in a variety of epidemiologic settings may also be necessary to understand the determinants of the full range of malarial illness. While a tremendous amount has been and can still be learned from cross-sectional studies, many of the questions that remain can only be addressed by monitoring larger numbers of people over longer periods of time, such as has been done in Senegal, 6 Ghana, 7 and Nigeria. 8A study initiated in June 1992 in western Kenya was designed to address the epidemiology, entomology, immunology (both humoral and cellular responses to defined antigens), host factors, molecular biology and antigenic variation, and population genetics of P. falciparum in a large cohort of women, newborn infants, and older children monitored over an extended period. Taken as a whole, this project wil...

The silent threat: asymptomatic parasitemia and malaria transmission

“…For example, in western Kenya, despite more than 10 years with high coverage of ITNs, parasite prevalence in children <5 years of age had declined from 83% in 1992 to only 41% by slide microscopy in 2009 [5,6]. Similar observations have been noted in areas formerly considered as high-transmission areas, such as Zambia [7] and Uganda [8].…”

Prevalence and Severity of Malnutrition in Pre-School Children in a Rural Area of Western Kenya

“…Malaria transmission is intense and occurs throughout the year. 13,14 The prevalence of HIV among pregnant women in this community was 18% in 1992−1996 (Kenya Medical Research Institute/Centers for Disease Control and Prevention, unpublished data). Approximately 5−9% of infants overall would be expected to be infected with HIV, assuming 25−48% motherto-child transmission in the context of extended breastfeeding.…”

ASSOCIATION OF INTERFERON-γ RESPONSES TO PRE-ERYTHROCYTIC STAGE VACCINE CANDIDATE ANTIGENS OF PLASMODIUM FALCIPARUM IN YOUNG KENYAN CHILDREN WITH IMPROVED HEMOGLOBIN LEVELS: XV. ASEMBO BAY COHORT PROJECT

“…This study was carried out as part of the Asembo Bay Cohort Project (ABCP) at Asembo Bay area in Nyanza province of western Kenya, recently described in detail elsewhere. 23 In this area, malaria transmission occurs throughout the year, with two peak transmission seasons from March to May and October to December. The annual entomologic inoculation rates have been reported to range between 100 and 300 per year, 24 and P. falciparum accounts for more than 90% of the malaria cases in this area.…”