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01.12.2012 | Research | Ausgabe 1/2012 Open Access

Malaria Journal 1/2012

Temporal and spatial patterns of serologic responses to Plasmodium falciparum antigens in a region of declining malaria transmission in southern Zambia

Zeitschrift:
Malaria Journal > Ausgabe 1/2012
Autoren:
Tamaki Kobayashi, Sandra Chishimba, Timothy Shields, Harry Hamapumbu, Sungano Mharakurwa, Philip E Thuma, Gregory Glass, William J Moss
Wichtige Hinweise

Electronic supplementary material

The online version of this article (doi:10.​1186/​1475-2875-11-438) contains supplementary material, which is available to authorized users.

Competing interests

The authors declare that they have no competing interests.

Authors’ contributions

TK participated in the coordination of the study, performed the data analysis and drafted the manuscript. SC performed the enzyme immunoassays and reviewed the manuscript. TS participated in the spatial analyses and reviewed the manuscript. HH coordinated the data and specimen collection and reviewed the manuscript. SM supervised the laboratory assays and reviewed the manuscript. PET supervised the field activities and reviewed the manuscript. GG participated in the spatial analyses and reviewed the manuscript. WJM conceived of the study, participated in its design and coordination, and participated in the preparation of the manuscript. All authors read and approved the final manuscript.

Abstract

Background

Critical to sustaining progress in malaria control is comprehensive surveillance to identify outbreaks and prevent resurgence. Serologic responses to Plasmodium falciparum antigens can serve as a marker of recent transmission and serosurveillance may be feasible on a large scale.

Methods

Satellite images were used to construct a sampling frame for the random selection of households enrolled in prospective longitudinal and cross-sectional surveys in two study areas in Southern Province, Zambia, one in 2007 and the other in 2008 and 2009. Blood was collected and stored as dried spots from participating household members. A malaria rapid diagnostic test (RDT) was used to diagnose malaria. An enzyme immunoassay (EIA) was used to detect IgG antibodies to asexual stage P. falciparum whole parasite lysate using serum eluted from dried blood spots. The expected mean annual increase in optical density (OD) value for individuals with a documented prior history of recent malaria was determined using mixed models. SatScan was used to determine the spatial clustering of households with individuals with serological evidence of recent malaria, and these households were plotted on a malaria risk map.

Results

RDT positivity differed markedly between the study areas and years: 28% of participants for whom serologic data were available were RDT positive in the 2007 study area, compared to 8.1% and 1.4% in the 2008 and 2009 study area, respectively. Baseline antibody levels were measured in 234 participants between April and July 2007, 435 participants between February and December 2008, and 855 participants between January and December 2009. As expected, the proportion of seropositive individuals increased with age in each year. In a subset of participants followed longitudinally, RDT positivity at the prior visit was positively correlated with an increase in EIA OD values after adjusting for age in 2007 (0.261, p = 0.003) and in 2008 (0.116, p = 0.03). RDT positivity at the concurrent visit also was associated with an increase in EIA OD value in 2007 (mean increase 0.177, p = 0.002) but not in 2008 (−0.063, p =0.50). Households comprised of individuals with serologic evidence of recent malaria overlapped areas of high malaria risk for serologic data from 2009, when parasite prevalence was lowest.

Conclusions

Serological surveys to whole asexual P. falciparum antigens using blood collected as dried blood spots can be used to detect temporal and spatial patterns of malaria transmission in a region of declining malaria burden, and have the potential to identify focal areas of recent transmission.
Zusatzmaterial
Authors’ original file for figure 1
12936_2012_2590_MOESM1_ESM.tiff
Authors’ original file for figure 2
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Authors’ original file for figure 3
12936_2012_2590_MOESM3_ESM.tiff
Literatur
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