Submicroscopic Plasmodium prevalence in relation to malaria incidence in 20 villages in western Cambodia. (December 2017)

• Record Type: Journal Article
• Authors: Tripura, Rupam; Peto, Thomas; Veugen, Christianne; Nguon, Chea; Davoeung, Chan; James, Nicola; Dhorda, Mehul; Maude, Richard; Duanguppama, Jureeporn; Patumrat, Krittaya; Imwong, Mallika; Seidlein, Lorenz; Grobusch, Martin; White, Nicholas; Dondorp, Arjen
• Is Part Of: Malaria journal. Volume 16:Number 1(2017)
• Page Start: 1
• Page End: 12
• Publication Date: 2017-12
• Subjects: Malaria -- Plasmodium Falciparum -- Plasmodium vivax -- Asymptomatic -- Sub-clinical -- Sub-microscopic -- uPCR -- Cambodia; Malaria -- Periodicals; 616.9362
• DOI: 10.1186/s12936-017-1703-5
• Languages: English
• ISSNs: 1475-2875

Abstract

Abstract Background Cambodia has seen a marked reduction in the incidence ofPlasmodium falciparum over the past decade without a corresponding decline inPlasmodium vivax incidence. It is unknown to what extent local transmission is sustained by a chain of clinical and sub-clinical infections or by continued re-introduction via migration. Using an ultrasensitive molecular technique, 20 villages in western Cambodia were surveyed to detect the low season prevalence ofP. falciparum andP. vivax and local treatment records were reviewed. Methods During March to May 2015 cross-sectional surveys were conducted in 20 villages in Battambang, western Cambodia. Demographic and epidemiological data and venous blood samples were collected from 50 randomly selected adult volunteers in each village. Blood was tested forPlasmodium infections by rapid diagnostic test (RDT), microscopy and high volume (0.5 ml packed red blood cell) quantitative polymerase chain reaction (uPCR). Positive samples were analysed by nested PCR to determine thePlasmodium species. Malaria case records were collected from the Provincial Health Department and village malaria workers to determine incidence and migration status. Results Among the 1000 participants, 91 (9.1%) were positive for anyPlasmodium infection by uPCR, seven (0.7%) by microscopy, and two (0.2%) by RDT. uPCRP. vivax prevalence was 6.6%, P. falciparum 0.7%, and undeterminedPlasmodium species 1.8%. Being male (adjusted OR 2.0; 95% CI 1.2-3.4); being a young adult <30 years (aOR 2.1; 95% CI 1.3–3.4); recent forest travel (aOR 2.8; 95% CI 1.6–4.8); and, a history of malaria (aOR 5.2; 95% CI 2.5–10.7) were independent risk factors for parasitaemia. Of the clinical malaria cases diagnosed by village malaria workers, 43.9% (297/634) and 38.4% (201/523) were among migrants in 2013 and in 2014, respectively.Plasmodium vivax prevalence determined by uPCR significantly correlated with vivax malaria incidences in both 2014 and 2015 (p = 0.001 and 0.002, respectively), whereas no relationship was observed in falciparum malaria (p = 0.36 and p = 0.59, respectively). Discussion There was heterogeneity in the malaria parasite reservoir between villages, andPlasmodium prevalence correlated with subsequent malaria incidence. The association was attributable chiefly toP. vivax infections, which were nine-fold more prevalent thanP. falciparum infections. In the absence of a radical cure with 8-aminoquinolines, P. vivax transmission will continue even asP. falciparum prevalence declines. Migration was associated with over a third of incident cases of clinical malaria. Trial registration clinicaltrials.gov (NCT01872702). Registered 4 June 2013