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Open Access Research

Validation of oral fluid samples to monitor serological changes to Plasmodium falciparum: An observational study in southern Zambia

Alexis P Chidi1, Sandra Chishimba2, Tamaki Kobayashi1, Harry Hamapumbu2, Sungano Mharakurwa12, Philip E Thuma2 and William J Moss1*

Author Affiliations

1 Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA

2 Macha Research Trust, Choma, Zambia

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Malaria Journal 2011, 10:162  doi:10.1186/1475-2875-10-162

Published: 10 June 2011

Abstract

Background

In formerly endemic areas where malaria transmission has declined, levels of population immunity to Plasmodium falciparum provide information on continued malaria transmission and potentially susceptible populations. Traditional techniques for measuring serological responses to P. falciparum antigens use plasma or dried blood spots (DBS). These invasive procedures pose a biohazard and may be unacceptable to communities if performed frequently. The use of oral fluid (OF) samples to detect antibodies to P. falciparum antigens may be a more acceptable strategy to monitor changes in population immunity.

Methods

An enzyme immunoassay was optimized to detect antibodies to whole, asexual stage P. falciparum antigens. Optical density (OD) values from paired DBS and OF samples collected as part of a community-based survey of malaria parasitaemia were compared.

Results

Oral fluid and dried blood spot samples were collected from 53 participants in Southern Province, Zambia. Their ages ranged from 1 to 80 years and 45% were female. A statistically significant correlation (r = 0.79; P < 0.01) was observed between OD values from OF and DBS samples. The OF assay identified all DBS-confirmed positive and negative samples, resulting in 100% sensitivity and specificity.

Conclusions

Oral fluid is a valid alternative specimen for monitoring changes in antibodies to P. falciparum antigens. As OF collection is often more acceptable to communities, poses less of a biohazard than blood samples and can be performed by community volunteers, serological surveys using OF samples provide a strategy for monitoring population immunity in regions of declining malaria transmission.