Artemisinin-resistant falciparum malaria, defined by a slow-clearance phenotype and the presence of kelch13 mutants, has emerged in the Greater Mekong Subregion. Naturally acquired immunity to malaria clears parasites independent of antimalarial drugs. We hypothesized that between-and within-population variations in host immunity influence parasite clearance after artemisinin treatment and the interpretation of emerging artemisinin resistance. Antibodies specific to 12 Plasmodium falciparum sporozoite and blood-stage antigens were determined in 959 patients (from 11 sites in Southeast Asia) participating in a multinational cohort study assessing parasite clearance half-life (PCt 1/2 ) after artesunate treatment and kelch13 mutations. Linear mixed-effects modeling of pooled individual patient data assessed the association between antibody responses and PCt 1/2. P. falciparum antibodies were lowest in areas where the prevalence of kelch13 mutations and slow PCt 1/2 were highest [Spearman ρ = −0.90 (95% confidence interval, −0.97, −0.65), and Spearman ρ = −0.94 (95% confidence interval, −0.98, −0.77), respectively]. P. falciparum antibodies were associated with faster PCt 1/2 (mean difference in PCt 1/2 according to seropositivity, −0.16 to −0.65 h, depending on antigen); antibodies have a greater effect on the clearance of kelch13 mutant compared with wild-type parasites (mean difference in PCt 1/2 according to seropositivity, −0.22 to −0.61 h faster in kelch13 mutants compared with wild-type parasites). Naturally acquired immunity accelerates the clearance of artemisininresistant parasites in patients with falciparum malaria and may confound the current working definition of artemisinin resistance. Immunity may also play an important role in the emergence and transmission potential of artemisinin-resistant parasites.malaria | artemisinin | drug resistance | immunity | serology

Background: In endemic areas, pregnant women are highly susceptible to Plasmodium falciparum malaria characterized by the accumulation of parasitized red blood cells (pRBC) in the placenta. In subsequent pregnancies, women develop protective immunity to pregnancy-associated malaria and this has been hypothesized to be due to the acquisition of antibodies to the parasite variant surface antigen VAR2CSA. In this systematic review we provide the first synthesis of the association between antibodies to pregnancy-specific P. falciparum antigens and pregnancy and birth outcomes. Methods: We conducted a systematic review and meta-analysis of population-based studies (published up to 07 June 2019) of pregnant women living in P. falciparum endemic areas that examined antibody responses to pregnancy-specific P. falciparum antigens and outcomes including placental malaria, low birthweight, preterm birth, peripheral parasitaemia, maternal anaemia, and severe malaria. Results: We searched 6 databases and identified 33 studies (30 from Africa) that met predetermined inclusion and quality criteria: 16 studies contributed estimates in a format enabling inclusion in meta-analysis and 17 were included in narrative form only. Estimates were mostly from cross-sectional data (10 studies) and were heterogeneous in terms of magnitude and direction of effect. Included studies varied in terms of antigens tested, methodology used to measure antibody responses, and epidemiological setting. Antibody responses to pregnancyspecific pRBC and VAR2CSA antigens, measured at delivery, were associated with placental malaria (9 studies) and may therefore represent markers of infection, rather than correlates of protection. Antibody responses to pregnancy-specific pRBC, but not recombinant VAR2CSA antigens, were associated with trends towards protection from low birthweight (5 studies). Conclusions: Whilst antibody responses to several antigens were positively associated with the presence of placental and peripheral infections, this review did not identify evidence that any specific antibody response is associated with protection from pregnancy-associated malaria across multiple populations. Further prospective cohort studies using standardized laboratory methods to examine responses to a broad range of antigens in different epidemiological settings and throughout the gestational period, will be necessary to identify and prioritize pregnancy-specific P. falciparum antigens to advance the development of vaccines and serosurveillance tools targeting pregnant women.

Background Woody tropical plants contain high levels of complex organic compounds that inhibit the chemical procedures needed to extract RNA or DNA, thus compromising downstream applications such as RNA sequencing and analysis of gene expression. To overcome this issue, researchers must use extraction protocols using CTAB/PVP buffer instead of commercially available DNA/RNA extraction kits. However, these protocols are time-consuming, use toxic chemicals like phenol and chloroform, and can only be used to process a small number of samples at a time. To overcome these issues, we developed a new CTAB/PVP based protocol for RNA or DNA extraction that eliminates the traditional phenol/chloroform step. Furthermore, the protocol was developed for 96-well plates to speed up processing. Results Our new protocol enabled us to successfully extract RNA from macadamia, avocado, and mango tissues that are traditionally difficult to work with. This RNA was then successfully used to synthesise cDNA for real-time quantitative PCR and to generate good quality RNA-Seq libraries. Our protocol can be easily converted for rapid DNA extraction from different tropical and sub-tropical tree species. Conclusion This method enables safer and faster DNA and RNA extraction from recalcitrant species, thus facilitating future work on tropical trees. Electronic supplementary material The online version of this article (10.1186/s13007-019-0447-3) contains supplementary material, which is available to authorized users.

Background: Identifying Plasmodium vivax antigen-specific antibodies associated with P. vivax infection and protective immunity is key to the development of serosurveillance tools and vaccines for malaria. Antibody targets of P. vivax can be identified by seroepidemiological studies of individuals living in P. vivax-endemic areas, and is an important strategy given the limited ability to culture P. vivax in vitro. There have been numerous studies investigating the association between P. vivax antibody responses and P. vivax infection, but there has been no standardization of results to enable comparisons across populations. Methods: We performed a systematic review with meta-analysis of population-based, cross-sectional, case-control, and cohort studies of individuals living in P. vivax-endemic areas. We searched 6 databases and identified 18 studies that met predefined inclusion and quality criteria, and examined the association between antibody responses to P. vivax antigens and P. vivax malaria.