History of malaria treatment as a predictor of subsequent subclinical parasitaemia: a cross-sectional survey and malaria case records from three villages in Pailin, western Cambodia

Abstract

BackgroundTreatment of the sub-clinical reservoir of malaria, which may maintain transmission, could be an important component of elimination strategies. The reliable detection of asymptomatic infections with low levels of parasitaemia requires high-volume quantitative polymerase chain reaction (uPCR), which is impractical to conduct on a large scale. It is unknown to what extent sub-clinical parasitaemias originate from recent or older clinical episodes. This study explored the association between clinical history of malaria and subsequent sub-clinical parasitaemia.MethodsIn June 2013 a cross-sectional survey was conducted in three villages in Pailin, western Cambodia. Demographic and epidemiological data and blood samples were collected. Blood was tested for malaria by high-volume qPCR. Positive samples were analysed by nested PCR to determine the Plasmodium species. To identify previous episodes of malaria, case records were collected from village malaria workers and local health facilities and linked to study participants.ResultsAmong 1343 participants, 40/122 (32.8 %) with a history of clinical malaria were parasitaemic during the cross-sectional survey, compared to 172/1221 (14.1 %) without this history (p < 0.001). Among the 212 parasitaemic participants in the survey, 40 (18.9 %) had a history of clinical malaria, compared to 87 out of 1131 (7.7 %) parasite-negative participants; p < 0.001, adjusted OR 3.3 (95 % CI; 2.1–5.1). A history of Plasmodium vivax was associated with sub-clinical P. vivax parasitaemia in the survey (p < 0.001), but this association was not seen with Plasmodium falciparum (p = 0.253); only three participants had both P. falciparum parasites in the survey and a clinical history of P. falciparum.ConclusionsA clinical episode of vivax malaria was associated with subsequent sub-clinical parasitaemia. Treatment of P. vivax with artemisinin-based combination therapy without primaquine often resulted in recurrent episodes. Targeting individuals with a history of clinical malaria will be insufficient to eliminate the sub-clinical reservoir as they constitute a minority of parasitaemias.

A multi-level spatial analysis of clinical malaria and subclinical Plasmodium infections in Pailin Province, Cambodia

“…Migration of both mosquitoes and humans can lead to the reintroduction of parasites to regions that might otherwise be malaria free [4] . A high prevalence of subclinical and submicroscopic Plasmodium infections, even in low transmission areas such as the GMS, undermines elimination efforts as these infections contribute to transmission and are unlikely to be detected and treated through conventional control activities [ 5 , 6 , 7 ].…”

Drama as a community engagement strategy for malaria in rural Cambodia

“…MORU has a long standing relationship with Cambodian health authorities. Since 2013, MORU has conducted malaria prevalence studies in villages in western Cambodia 18 , and since 2015, targeted malaria elimination studies involving mass drug administration has been on-going in villages in Western Cambodia 17 . All projects involve local stakeholders at the national, provincial and village level.…”

Maximizing research study effectiveness in malaria elimination settings: a mixed methods study to capture the experiences of field-based staff

“…Its highly mobile populations, compounded with particularly porous borders, facilitate the frequent importation and exportation of drug resistant parasites [ 22 ]. As is common in many malaria elimination settings, despite their higher burden of disease and their crucial role in its spread [ 23 ], MMPs in this region often slip through the cracks of passive malaria control measures aimed at the general population, and are often excluded from research studies because of the difficulty in conducting follow-up [ 24 ]. In a similar manner, participants who are labeled as “treatment failures” are also removed from the study and become ineligible for recruitment in future studies; in a drug-resistant setting like Western Cambodia, this is not infrequent.…”

“…In a similar manner, participants who are labeled as “treatment failures” are also removed from the study and become ineligible for recruitment in future studies; in a drug-resistant setting like Western Cambodia, this is not infrequent. The combination of low malaria incidence [ 14 ], a mobile and remote participant pool [ 24 ], and high rates of participant ineligibility due to mobility and recrudescence, results in a number of barriers to effective field research.…”