Journal Article

Serological markers for monitoring historical changes in malaria transmission intensity in a highly endemic region of Western Kenya, 1994–2009

Shi, Ya Ping, Drakeley, Chris J, Bloland, Peter B, Kariuki, Simon, Otieno, Kephas, Vulule, John M, Nahlen, Bernard L, Slutsker, Laurence, Otieno, Peter, Were, Vincent, Hamel, Mary J, Gimnig, John E, Wong, Jacklyn, Lal, Altaf A, Odero, Chris, Lindblade, Kim A

2014

Overview

Background Monitoring local malaria transmission intensity is essential for planning evidence-based control strategies and evaluating their impact over time. Anti-malarial antibodies provide information on cumulative exposure and have proven useful, in areas where transmission has dropped to low sustained levels, for retrospectively reconstructing the timing and magnitude of transmission reduction. It is unclear whether serological markers are also informative in high transmission settings, where interventions may reduce transmission, but to a level where considerable exposure continues. Methods This study was conducted through ongoing KEMRI and CDC collaboration. Asembo, in Western Kenya, is an area where intense malaria transmission was drastically reduced during a 1997–1999 community-randomized, controlled insecticide-treated net (ITN) trial. Two approaches were taken to reconstruct malaria transmission history during the period from 1994 to 2009. First, point measurements were calculated for seroprevalence, mean antibody titre, and seroconversion rate (SCR) against three Plasmodium falciparum antigens (AMA-1, MSP-1 19 , and CSP) at five time points for comparison against traditional malaria indices (parasite prevalence and entomological inoculation rate). Second, within individual post-ITN years, age-stratified seroprevalence data were analysed retrospectively for an abrupt drop in SCR by fitting alternative reversible catalytic conversion models that allowed for change in SCR. Results Generally, point measurements of seroprevalence, antibody titres and SCR produced consistent patterns indicating that a gradual but substantial drop in malaria transmission (46-70%) occurred from 1994 to 2007, followed by a marginal increase beginning in 2008 or 2009. In particular, proportionate changes in seroprevalence and SCR point estimates (relative to 1994 baseline values) for AMA-1 and CSP, but not MSP-1 19 , correlated closely with trends in parasite prevalence throughout the entire 15-year study period. However, retrospective analyses using datasets from 2007, 2008 and 2009 failed to detect any abrupt drop in transmission coinciding with the timing of the 1997–1999 ITN trial. Conclusions In this highly endemic area, serological markers were useful for generating accurate point estimates of malaria transmission intensity, but not for retrospective analysis of historical changes. Further investigation, including exploration of different malaria antigens and/or alternative models of population seroconversion, may yield serological tools that are more informative in high transmission settings.

• Publisher: BioMed Central,BioMed Central Ltd,Springer Nature B.V
• Subject: Adolescent / Adult / Aged / Aged, 80 and over / Analysis / Antibodies / Antibodies, Protozoan - blood / Antigens / Antigens, Protozoan - immunology / Biomedical and Life Sciences / Biomedicine / Care and treatment / Child / Child, Preschool / Disease transmission / Distribution / Entomology / Epidemiology / Health aspects / Health facilities / Health services / Humans / Image processing / Infant / Infections / Infectious Diseases / Insecticides / Intervention / Kenya - epidemiology / Malaria / Malaria, Falciparum - epidemiology / Malaria, Falciparum - transmission / Male / Medical research / Membrane Proteins - immunology / Merozoite Surface Protein 1 - immunology / Microbiology / Middle Aged / Mortality / Mosquitoes / Parasites / Parasitic diseases / Parasitology / Plasmodium falciparum / Plasmodium falciparum - immunology / Protozoan Proteins - immunology / Public Health / Retrospective Studies / Risk factors / Seroepidemiologic Studies / Statistical analysis / Studies / Tropical Medicine / Vector-borne diseases / Viral antibodies / Young Adult