Detectability of Plasmodium falciparum clones.


Bretscher, MT; Valsangiacomo, F; Owusu-Agyei, S; Penny, MA; Felger, I; Smith, T; (2010) Detectability of Plasmodium falciparum clones. Malar J, 9. p. 234. ISSN 1475-2875 DOI: 10.1186/1475-2875-9-234

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Abstract

BACKGROUND In areas of high transmission people often harbour multiple clones of Plasmodium falciparum, but even PCR-based diagnostic methods can only detect a fraction (the detectability, q) of all clones present in a host. Accurate measurements of detectability are desirable since it affects estimates of multiplicity of infection, prevalence, and frequency of breakthrough infections in clinical drug trials. Detectability can be estimated by typing repeated samples from the same host but it has been unclear what should be the time interval between the samples and how the data should be analysed. METHODS A longitudinal molecular study was conducted in the Kassena-Nankana district in northern Ghana. From each of the 80 participants, four finger prick samples were collected over a period of 8 days, and tested for presence of different Merozoite Surface Protein (msp) 2 genotypes. Implications for estimating q were derived from these data by comparing the fit of statistical models of serial dependence and over-dispersion. RESULTS The distribution of the frequencies of detection for msp2 genotypes was close to binomial if the time span between consecutive blood samples was at least 7 days. For shorter intervals the probabilities of detection were positively correlated, i.e. the shorter the interval between two blood collections, the more likely the diagnostic results matched for a particular genotype. Estimates of q were rather insensitive to the statistical model fitted. CONCLUSIONS A simple algorithm based on analysing blood samples collected 7 days apart is justified for generating robust estimates of detectability. The finding of positive correlation of detection probabilities for short time intervals argues against imperfect detection being directly linked to the 48-hour periodicity of P. falciparum. The results suggest that the detectability of a given parasite clone changes over time, at an unknown rate, but fast enough to regard blood samples taken one week apart as statistically independent.

Item Type: Article
Faculty and Department: Faculty of Infectious and Tropical Diseases > Dept of Disease Control
Faculty of Infectious and Tropical Diseases > Dept of Immunology and Infection
PubMed ID: 20718959
Web of Science ID: 282416200001
URI: http://researchonline.lshtm.ac.uk/id/eprint/333634

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