Persistent Plasmodium falciparum and Plasmodium vivax infections in a western Cambodian population: implications for prevention, treatment and elimination strategies.

Background Subclinical Plasmodium parasitaemia is an important reservoir for the transmission and persistence of malaria, particularly in low transmission areas. Methods Using 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. Results The 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. Conclusions This 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.