Antibody Profiles to P. falciparum Antigens Over Time Characterize Acute and Long-Term Malaria Exposure in an Area of Low and Unstable Transmission

Abstract

Prevalence and levels of antibodies to multiple Plasmodium falciparum antigens show promise as tools for estimating malaria exposure. In a highland area of Kenya with unstable transmission, we assessed the presence and levels of antibodies to 12 pre-erythrocytic and blood-stage P. falciparum antigens by multiplex cytometric bead assay or ELISA in 604 individuals in August 2007, with follow-up testing in this cohort in April 2008, April 2009, and May 2010. Four hundred individuals were tested at all four time points. During this period, the only substantial malaria incidence occurred from April to August 2009. Antibody prevalence in adults was high at all time points (> 70%) for apical membrane antigen 1, erythrocyte-binding antigen 175, erythrocyte-binding protein-2, glutamate rich protein (GLURP)-R2, merozoite surface protein (MSP) 1 (19), MSP-1 (42), and liver-stage antigen-1; moderate (30-70%) for GLURP-R0, MSP-3, and thrombospondin-related adhesive protein; and low (< 30%) for SE and circumsporozoite protein (CSP). Changes in community-wide malaria exposure were best reflected in decreasing antibody levels overtime for highly immunogenic antigens, and in antibody seroprevalence overtime for the less-immunogenic antigens. Over the 3 years, antibody levels to all antigens except CSP and schizont extract (SE) decreased in an age-dependent manner. Prevalence and levels of antibodies to all antigens except CSP and SE increased with age. Increases in antibody prevalence and levels to CSP and SE coincided with increases in community-wide malaria incidence. Antibody levels to multiple P. falciparum antigens decrease in the absence of consistent transmission. Multiplex assays that assess both the presence and level of antibodies to multiple pre-erythrocytic and blood-stage P. falciparum antigens may provide the most useful estimates of past and recent malaria transmission in areas of unstable transmission and could be useful tools in malaria control and elimination campaigns.

Figure 1.

Clinical malaria incidence overtime per 1,000 persons in Kipsamoite and Kapsisiywa, Kenya. A spike in malaria incidence occurred between April 2009 and May 2010, a period within our blood collection time points and antibody testing.

Figure 2.

Waning of seroprevalence overtime. In 4 cross-sectional cohorts with repeatedly sampled individuals, seroprevalence to 12 Plasmodium falciparum antigens reduced overtime. Points represent the proportion seropositive in three age-groups from each of the four cross sections, with 95% CIs represented by vertical bars. Lines represent the fit of models of waning seroprevalence.

Figure 3.

Waning of antibody levels overtime. In four cross-sectional cohorts with repeatedly sampled individuals, antibody levels to 12 Plasmodium falciparum antigens reduced overtime. Points represent the geometric mean antibody levels in three age groups from each of the four cross sections, with 95% CIs represented by vertical bars. Lines represent the fit of mixed-effects linear regression models to the data.