Contribution to Malaria Transmission of Symptomatic and Asymptomatic Parasite Carriers in Cambodia.

Background: Eliminating falciparum malaria in Cambodia is a top priority, requiring the implementation of novel tools and strategies to interrupt its transmission. To date, few data are available regarding the contributions to malaria transmission of symptomatic and asymptomatic carriers. Methods: Direct-membrane and skin feeding assays (DMFAs, SFAs) were performed, using Anopheles minimus and Anopheles dirus, to determine infectivity of symptomatic falciparum-infected patients and malaria asymptomatic carriers; a subset of the latter were followed up for 2 months to assess their transmission potential. Results: By microscopy and real-time polymerase chain reaction, Plasmodium falciparum gametocyte prevalence rates were, respectively, 19.3% (n = 21/109) and 44% (n = 47/109) on day (D) 0 and 17.9% (n = 5/28) and 89.3% (n = 25/28) in recrudescent patients (Drec) (RT-PCR Drec vs D0 P = .002). Falciparum malaria patient infectivity was low on D0 (6.2%; n = 3/48) and in Drec (8.3%; n = 1/12). Direct-membrane feeding assays and SFAs gave similar results. None of the falciparum (n = 0/19) and 3 of 28 Plasmodium vivax asymptomatic carriers were infectious to mosquitoes, including those that were followed up for 2 months. Overall, P. falciparum gametocytemias were low except in a few symptomatic carriers. Conclusions: Only symptomatic falciparum malaria patients were infectious to mosquito vectors at baseline and recrudescence, highlighting the need to detect promptly and treat effectively P. falciparum patients.

Therapeutic and Transmission-Blocking Efficacy of Dihydroartemisinin/Piperaquine and Chloroquine against Plasmodium vivax Malaria, Cambodia.

We assessed the efficacy of standard 3-day courses of chloroquine and dihydroartemisinin/piperaquine against Plasmodium vivax malaria. Compared with chloroquine, dihydroartemisinin/piperaquine was faster in clearing asexual P. vivax parasites and blocking human-to-mosquito transmission. This drug combination was also more effective in preventing potential recurrences for >2 months.

Characterization of P. vivax blood stage transcriptomes from field isolates reveals similarities among infections and complex gene isoforms.

Our understanding of the structure and regulation of Plasmodium vivax genes is limited by our inability to grow the parasites in long-term in vitro cultures. Most P. vivax studies must therefore rely on patient samples, which typically display a low proportion of parasites and asynchronous parasites. Here, we present stranded RNA-seq data generated directly from a small volume of blood from three Cambodian vivax malaria patients collected before treatment. Our analyses show surprising similarities of the parasite gene expression patterns across infections, despite extensive variations in parasite stage proportion. These similarities contrast with the unique gene expression patterns observed in sporozoites isolated from salivary glands of infected Colombian mosquitoes. Our analyses also indicate that more than 10% of P. vivax genes encode multiple, often undescribed, protein-coding sequences, potentially increasing the diversity of proteins synthesized by blood stage parasites. These data also greatly improve the annotations of P. vivax gene untranslated regions, providing an important resource for future studies of specific genes.