Abstract
BackgroundSubclinical Plasmodium parasitaemia is an important reservoir for the transmission and persistence of malaria, particularly in low transmission areas.MethodsUsing ultrasensitive quantitative PCR (uPCR) for the detection of parasitaemia, the entire population of three Cambodian villages in Pailin province were followed for 1 year at three-monthly intervals. A cohort of adult participants found initially to have asymptomatic malaria parasitaemia was followed monthly over the same period.ResultsThe initial cross sectional survey in June 2013 (M0) of 1447 asymptomatic residents found that 32 (2.2 %) had Plasmodium falciparum, 48 (3.3 %) had P. vivax, 4 (0.3 %) had mixed infections and in 142/1447 (9.8 %) malaria was detected but there was insufficient DNA to identify the species (Plasmodium. species). Polymorphisms in the ‘K13-propeller’ associated with reduced susceptibility to artemisinin derivatives (C580Y) were found in 17/32 (51 %) P. falciparum strains. Monthly follow-up without treatment of 24 adult participants with asymptomatic mono or mixed P. falciparum infections found that 3/24 (13 %) remained parasitaemic for 2–4 months, whereas the remaining 21/24 (87 %) participants had cleared their parasitaemia after 1 month. In contrast, 12/34 (35 %) adult participants with P. vivax mono-infection at M0 had malaria parasites (P. vivax or P. sp.) during four or more of the following 11 monthly surveys.ConclusionsThis longitudinal survey in a low transmission setting shows limited duration of P. falciparum carriage, but prolonged carriage of P. vivax infections. Radical treatment of P. vivax infections by 8-aminoquinoline regimens may be required to eliminate all malaria from Cambodia.Trial registration ClinicalTrials.gov NCT01872702Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-016-1224-7) contains supplementary material, which is available to authorized users.
Highlights
Subclinical Plasmodium parasitaemia is an important reservoir for the transmission and persistence of malaria, in low transmission areas
Deforestation and standard malaria control efforts including early, appropriate case management and distribution of insecticide-treated bed nets have reduced malaria prevalence to historically low levels in much of Western Cambodia. These control measures have failed to contain the emergence of anti-malarial drug resistant strains of Plasmodium falciparum in an expanding geographical area [1, 2]
Containment efforts in Cambodia have resulted in a marked decline in the incidence of clinical malaria over the last decade
Summary
Subclinical Plasmodium parasitaemia is an important reservoir for the transmission and persistence of malaria, in low transmission areas. Deforestation and standard malaria control efforts including early, appropriate case management and distribution of insecticide-treated bed nets have reduced malaria prevalence to historically low levels in much of Western Cambodia. These control measures have failed to contain the emergence of anti-malarial drug resistant strains of Plasmodium falciparum in an expanding geographical area [1, 2]. Malaria has historically been difficult to eliminate even when most symptomatic patients received highly effective anti-malarial treatments. Symptomatic infections as a sole source of transmission cannot explain the virtual disappearance of malaria cases each year during the cool dry season and prompt return with the onset of rains. To understand and eliminate such a reservoir it is important to understand the prevalence at any one point in time and the duration of individual infections
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