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J Infect Dis. 2016 Apr 15;213(8):1322-9. doi: 10.1093/infdis/jiv596. Epub 2015 Dec 17.

Numerical Distributions of Parasite Densities During Asymptomatic Malaria.

Author information

1
Mahidol Oxford Research Unit Department of Molecular Tropical Medicine and Genetics.
2
Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford WWARN, Churchill Hospital, Oxford, United Kingdom.
3
Mahidol Oxford Research Unit.
4
Shoklo Malaria Research Unit, Faculty of Tropical Medicine, Mahidol University, Tak, Thailand.
5
Mahidol Oxford Research Unit Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford.
6
WorldWide Antimalarial Resistance Network (WWARN).
7
Sorbonne Universités, UPMC Univ Paris 06, UPMC UMRS CR7 Centre d'Immunologie et de Maladies Infectieuses-Paris, Institut National de la Santé et de la Recherche Medicale U1135-Centre National de la Recherche Scientifique ERL 8255, Paris, France.
8
Department of Tropical Hygiene, Faculty of Tropical Medicine, Mahidol University, Bangkok.
9
National Center for Parasitology, Entomology, and Malaria Control, Phnom Penh, Cambodia.
10
Mahidol Oxford Research Unit Shoklo Malaria Research Unit, Faculty of Tropical Medicine, Mahidol University, Tak, Thailand Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford.

Abstract

BACKGROUND:

Asymptomatic parasitemia is common even in areas of low seasonal malaria transmission, but the true proportion of the population infected has not been estimated previously because of the limited sensitivity of available detection methods.

METHODS:

Cross-sectional malaria surveys were conducted in areas of low seasonal transmission along the border between eastern Myanmar and northwestern Thailand and in western Cambodia. DNA was quantitated by an ultrasensitive polymerase chain reaction (uPCR) assay (limit of accurate detection, 22 parasites/mL) to characterize parasite density distributions for Plasmodium falciparum and Plasmodium vivax, and the proportions of undetected infections were imputed.

RESULTS:

The prevalence of asymptomatic malaria as determined by uPCR was 27.5% (1303 of 4740 people tested). Both P. vivax and P. falciparum density distributions were unimodal and log normal, with modal values well within the quantifiable range. The estimated proportions of all parasitemic individuals identified by uPCR were >70% among individuals infected with P. falciparum and >85% among those infected with P. vivax. Overall, 83% of infections were predicted to be P. vivax infections, 13% were predicted to be P. falciparum infections, and 4% were predicted to be mixed infections. Geometric mean parasite densities were similar; 5601 P. vivax parasites/mL and 5158 P. falciparum parasites/mL.

CONCLUSIONS:

This uPCR method identified most infected individuals in malaria-endemic areas. Malaria parasitemia persists in humans at levels that optimize the probability of generating transmissible gametocyte densities without causing illness.

KEYWORDS:

PCR; Plasmodium falciparum; Plasmodium vivax; asymptomatic parasitemia; malaria

PMID:
26681777
PMCID:
PMC4799672
DOI:
10.1093/infdis/jiv596
[Indexed for MEDLINE]
Free PMC Article

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