Limited threat of Plasmodium falciparum pfhrp2 and pfhrp3 gene deletion to the utility of HRP2-based malaria RDTs in Northern Uganda.

BACKGROUND: Rapid diagnostic tests (RDTs) that detect Plasmodium falciparum histidine-rich protein-2 (PfHRP2) are exclusively deployed in Uganda, but deletion of the pfhrp2/3 target gene threatens their usefulness as malaria diagnosis and surveillance tools. METHODS: A cross-sectional survey was conducted at 40 sites across four regions of Uganda in Acholi, Lango, W. Nile and Karamoja from March 2021 to June 2023. Symptomatic malaria suspected patients were recruited and screened with both HRP2 and pan lactate dehydrogenase (pLDH) detecting RDTs. Dried blood spots (DBS) were collected from all patients and a random subset were used for genomic analysis to confirm parasite species and pfhrp2 and pfhrp3 gene status. Plasmodium species was determined using a conventional multiplex PCR while pfhrp2 and pfhrp3 gene deletions were determined using a real-time multiplex qPCR. Expression of the HRP2 protein antigen in a subset of samples was further assessed using a ELISA. RESULTS: Out of 2435 symptomatic patients tested for malaria, 1504 (61.8%) were positive on pLDH RDT. Overall, qPCR confirmed single pfhrp2 gene deletion in 1 out of 416 (0.2%) randomly selected samples that were confirmed of P. falciparum mono-infections. CONCLUSION: These findings show limited threat of pfhrp2/3 gene deletions in the survey areas suggesting that HRP2 RDTs are still useful diagnostic tools for surveillance and diagnosis of P. falciparum malaria infections in symptomatic patients in this setting. Periodic genomic surveillance is warranted to monitor the frequency and trend of gene deletions and its effect on RDTs.

A cross-sectional survey of knowledge and attitudes towards scabies control in Australian aged care facilities.

Scabies outbreaks cause significant morbidity and disruption in aged care facilities and other institutional settings. Failure to manage scabies outbreaks may be attributable to low awareness amongst healthcare workers. A survey was distributed to healthcare workers across aged care facilities in South-East Queensland, Australia. The survey captured demographics, prior scabies experience, knowledge-based questions, and attitudes. Scabies was common in aged care facilities, with 41% of 128 respondents encountering the disease while working in aged care. Participants demonstrated sound theoretical knowledge regarding scabies (median knowledge score 82%). Scabies knowledge was not associated with years of experience in the sector or educational level but was associated with respondent age (p = 0.017). Knowledge gaps were evident regarding diagnosis, incubation periods, and treatment. Respondents demonstrated an inconsistent ability to identify atypical clinical presentations of scabies, showing discordance between theoretical knowledge and its practical application. The ability to identify crusted scabies was low, reflecting the high frequency of misdiagnosis of index cases in scabies outbreaks. Respondents considered scabies to be a problem and were supportive of improved management guidelines. These study outcomes will inform the design of accessible, targeted educational resources for scabies to help prevent and reduce the impact of outbreaks.

Children's scabies survey indicates high prevalence and misdiagnosis in Auckland educational institutions.

AIM: Here, we present results of a survey of scabies prevalence in childcare centres and primary schools in Auckland. METHODS: Children whose parents agreed to take part in participating centres in the Auckland region were examined for scabies by general practitioners and given questionnaires of relevant symptoms. Diagnoses of clinical or suspected scabies were made according to the International Alliance for the Control of Scabies (IACS) criteria. The survey was a stratified random sample of schools and early childcare centres. A quantitative polymerase chain reaction (PCR) test was also used to complement the IACS criteria. RESULTS: A total of 181 children were examined, with 145 children with history information, 16 of whom (11.0%) met the criteria for 'clinical' or 'suspected' scabies. Weighted analysis, accounting for the survey design, indicated that the prevalence of scabies in early childcare centres was 13.2% (95% CI: 4.3 to 22.1), with no school-aged children fulfilling these criteria. A higher proportion had clinical signs of scabies with 23 (12.7%) having typical scabies lesions and a further 43 (23.8%) had atypical lesions. A total of 64 PCR tests were taken and 15 (23%) were positive. None of these cases were receiving treatment for scabies. Five were undergoing topical skin treatment: three with topical steroid and two with calamine lotion. CONCLUSIONS: The prevalence of children with scabies is high in early childcare centres in Auckland. Misdiagnosis is suggested by several PCR positive cases being treated by topical agents used to treat other skin conditions.

Safety and parasite clearance of artemisinin-resistant Plasmodium falciparum infection: A pilot and a randomised volunteer infection study in Australia.

BACKGROUND: Artemisinin resistance is threatening malaria control. We aimed to develop and test a human model of artemisinin-resistant (ART-R) Plasmodium falciparum to evaluate the efficacy of drugs against ART-R malaria. METHODS AND FINDINGS: We conducted 2 sequential phase 1, single-centre, open-label clinical trials at Q-Pharm, Brisbane, Australia, using the induced blood-stage malaria (IBSM) model, whereby healthy participants are intravenously inoculated with blood-stage parasites. In a pilot study, participants were inoculated (Day 0) with approximately 2,800 viable P. falciparum ART-R parasites. In a comparative study, participants were randomised to receive approximately 2,800 viable P. falciparum ART-R (Day 0) or artemisinin-sensitive (ART-S) parasites (Day 1). In both studies, participants were administered a single approximately 2 mg/kg oral dose of artesunate (AS; Day 9). Primary outcomes were safety, ART-R parasite infectivity, and parasite clearance. In the pilot study, 2 participants were enrolled between April 27, 2017, and September 12, 2017, and included in final analyses (males n = 2 [100%], mean age = 26 years [range, 23-28 years]). In the comparative study, 25 participants were enrolled between October 26, 2017, and October 18, 2018, of whom 22 were inoculated and included in final analyses (ART-R infected participants: males n = 7 [53.8%], median age = 22 years [range, 18-40 years]; ART-S infected participants: males n = 5 [55.6%], median age = 28 years [range, 22-35 years]). In both studies, all participants inoculated with ART-R parasites became parasitaemic. A total of 36 adverse events were reported in the pilot study and 277 in the comparative study. Common adverse events in both studies included headache, pyrexia, myalgia, nausea, and chills; none were serious. Seven participants experienced transient severe falls in white cell counts and/or elevations in liver transaminase levels which were considered related to malaria. Additionally, 2 participants developed ventricular extrasystoles that were attributed to unmasking of a predisposition to benign fever-induced tachyarrhythmia. In the comparative study, parasite clearance half-life after AS was significantly longer for ART-R infected participants (n = 13, 6.5 hours; 95% confidence interval [CI] 6.3-6.7 hours) compared with ART-S infected participants (n = 9, 3.2 hours; 95% CI 3.0-3.3 hours; p < 0.001). The main limitation of this study was that the ART-R and ART-S parasite strains did not share the same genetic background. CONCLUSIONS: We developed the first (to our knowledge) human model of ART-R malaria. The delayed clearance profile of ART-R parasites after AS aligns with field study observations. Although based on a relatively small sample size, results indicate that this model can be safely used to assess new drugs against ART-R P. falciparum. TRIAL REGISTRATION: The studies were registered with the Australian New Zealand Clinical Trials Registry: ACTRN12617000244303 (https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=372357) and ACTRN12617001394336 (https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=373637).

Polymorphisms in Plasmodium falciparum Kelch 13 and P. vivax Kelch 12 Genes in Parasites Collected from Three South Pacific Countries Prior to Extensive Exposure to Artemisinin Combination Therapies.

The South Pacific countries Solomon Islands, Vanuatu, and Papua New Guinea (PNG) adopted artemisinin-based combination therapies (ACTs) in 2008. We examined Kelch 13 and Kelch 12 genes in parasites originating from these countries before or at ACT introduction. Four Kelch 13 and two Kelch 12 novel sequence polymorphisms, not associated with artemisinin resistance, were observed in parasites from Solomon Islands and Vanuatu. No polymorphisms were observed in PNG parasites. The findings provide useful baseline information.

Cyclooctatetraene: A Bioactive Cubane Paradigm Complement.

Cubane was recently validated as a phenyl ring (bio)isostere, but highly strained caged carbocyclic systems lack π character, which is often critical for mediating key biological interactions. This electronic property restriction associated with cubane has been addressed herein with cyclooctatetraene (COT), using known pharmaceutical and agrochemical compounds as templates. COT either outperformed or matched cubane in multiple cases suggesting that versatile complementarity exists between the two systems for enhanced bioactive molecule discovery.

A bioreactor system for the manufacture of a genetically modified Plasmodium falciparum blood stage malaria cell bank for use in a clinical trial.

BACKGROUND: Although the use of induced blood stage malaria infection has proven to be a valuable tool for testing the efficacy of vaccines and drugs against Plasmodium falciparum, a limiting factor has been the availability of Good Manufacturing Practice (GMP)-compliant defined P. falciparum strains for in vivo use. The aim of this study was to develop a cost-effective method for the large-scale production of P. falciparum cell banks suitable for use in clinical trials. METHODS: Genetically-attenuated parasites (GAP) were produced by targeted deletion of the gene encoding the knob associated histidine rich protein (kahrp) from P. falciparum strain 3D7. A GAP master cell bank (MCB) was manufactured by culturing parasites in an FDA approved single use, closed system sterile plastic bioreactor. All components used to manufacture the MCB were screened to comply with standards appropriate for in vivo use. The cryopreserved MCB was subjected to extensive testing to ensure GMP compliance for a phase 1 investigational product. RESULTS: Two hundred vials of the GAP MCB were successfully manufactured. At harvest, the GAP MCB had a parasitaemia of 6.3%, with 96% of parasites at ring stage. Testing confirmed that all release criteria were met (sterility, absence of viral contaminants and endotoxins, parasite viability following cryopreservation, identity and anti-malarial drug sensitivity of parasites). CONCLUSION: Large-scale in vitro culture of P. falciparum parasites using a wave bioreactor can be achieved under GMP-compliant conditions. This provides a cost-effective methodology for the production of malaria parasites suitable for administration in clinical trials.

Piperaquine Monotherapy of Drug-Susceptible Plasmodium falciparum Infection Results in Rapid Clearance of Parasitemia but Is Followed by the Appearance of Gametocytemia.

BACKGROUND: Piperaquine, coformulated with dihydroartemisinin, is a component of a widely used artemisinin combination therapy. There is a paucity of data on its antimalarial activity as a single agent. Such data, if available, would inform selection of new coformulations. METHODS: We undertook a study in healthy subjects, using the induced blood stage malaria (IBSM) model to test the antimalarial activity of single doses of piperaquine (960, 640, and 480 mg) in 3 cohorts. In a pilot study in the third cohort, gametocyte clearance following administration of 15 mg, or 45 mg or no primaquine was investigated. RESULTS: Parasite clearance over the 48-hour period after piperaquine administration was more rapid in the 960 mg cohort, compared with the 640 mg cohort (parasite reduction ratio, 2951 [95% confidence interval {CI}, 1520-5728] vs 586 [95% CI, 351-978]; P < .001). All 24 subjects developed gametocytemia as determined by pfs25 transcripts. Clearance of pfs25 was significantly faster in those receiving primaquine than in those not receiving primaquine (P < .001). CONCLUSIONS: Piperaquine possesses rapid parasite-clearing activity, but monotherapy is followed by the appearance of gametocytemia, which could facilitate the spread of malaria. This new information should be taken into account when developing future antimalarial coformulations. CLINICAL TRIALS REGISTRATION: ACTRN12613000565741.

Validating Eaton's Hypothesis: Cubane as a Benzene Bioisostere.

Pharmaceutical and agrochemical discovery programs are under considerable pressure to meet increasing global demand and thus require constant innovation. Classical hydrocarbon scaffolds have long assisted in bringing new molecules to the market place, but an obvious omission is that of the Platonic solid cubane. Eaton, however, suggested that this molecule has the potential to act as a benzene bioisostere. Herein, we report the validation of Eaton's hypothesis with cubane derivatives of five molecules that are used clinically or as agrochemicals. Two cubane analogues showed increased bioactivity compared to their benzene counterparts whereas two further analogues displayed equal bioactivity, and the fifth one demonstrated only partial efficacy. Ramifications from this study are best realized by reflecting on the number of bioactive molecules that contain a benzene ring. Substitution with the cubane scaffold where possible could revitalize these systems, and thus expedite much needed lead candidate identification.

Comparison of prevalence estimates of pfhrp2 and pfhrp3 deletions in Plasmodium falciparum determined by conventional PCR and multiplex qPCR and implications for surveillance and monitoring.

OBJECTIVES: The accuracy of malaria rapid diagnostic tests is threatened by Plasmodium falciparum with pfhrp2/3 deletions. This study compares gene deletion prevalence determined by multiplex real time polymerase chain reaction (qPCR) and conventional polymerase chain reaction (cPCR) using existing samples with clonality previously determined by microsatellite genotyping. METHODS: Multiplex qPCR was used to estimate prevalence of pfhrp2/3 deletions in three sets of previously collected patient samples from Eritrea and Peru. The qPCR was validated by multiplex digital polymerase chain reaction. Sample classification was compared with cPCR, and receiver operating characteristic curve analysis was used to determine the optimal ΔCq threshold that aligned the results of the two assays. RESULTS: qPCR classified 75% (637 of 849) of samples as single, and 212 as mixed-pfhrp2/3 genotypes, with a positive association between clonality and proportion of mixed-pfhrp2/3 genotype samples. The sample classification agreement between cPCR and qPCR was 75.1% (95% confidence interval [CI] 68.6-80.7%) and 47.8% (95% CI 38.9-56.9%) for monoclonal and polyclonal infections. The qPCR prevalence estimates of pfhrp2/3 deletions showed almost perfect (κ = 0.804, 95% CI 0.714-0.895) and substantial agreement (κ = 0.717, 95% CI 0.562-0.872) with cPCR for Peru and 2016 Eritrean samples, respectively. For 2019 Eritrean samples, the prevalence of double pfhrp2/3 deletions was approximately two-fold higher using qPCR. The optimal threshold for matching the assay results was ΔCq = 3. CONCLUSIONS: Multiplex qPCR and cPCR produce comparable estimates of gene deletion prevalence when monoclonal infections dominate; however, qPCR provides higher estimates where multi-clonal infections are common.

High prevalence of scabies in Auckland pre-schools.

AIM: Scabies is a difficult disease to diagnose and its prevalence not well established. A strong association between scabies and more serious illnesses in children, for instance acute rheumatic fever, suggests greater understanding of scabies prevalence is warranted. Here, we present initial findings of a study of childcare centres, to estimate the prevalence of scabies in the Auckland community. METHODS: Children in three childcare centres from socio-economically challenged areas were examined for scabies. Diagnoses were made according to the International Alliance for the Control of Scabies (IACS) criteria, whose "clinical" or "suspected" definition consists of examination findings of papules: either "typical" or "atypical" distribution, along with history features of itch and contact with likely other cases. A quantitative polymerase chain reaction (qPCR) test was also used. RESULTS: A total of 67 children were examined, with over half (n=38 or 56.7%) showing signs of typical (14; 20.9%) or atypical (24; 35.8%) scabies lesions. History information was available for 50 children. Of these, nine (18%) met the criteria for "clinical" or "suspected" scabies. Of 27 qPCR tests performed nine (33%) tested positive. CONCLUSION: The prevalence of scabies is high in early childcare centres in socio-economically challenged areas of Auckland.

Spatiotemporal dynamics of Plasmodium falciparum histidine-rich protein 2 and 3 deletions in Peru.

Peru was the first country where pfhrp2 and pfhrp3 gene deletions were detected despite the fact that rapid diagnostics tests are not commonly used for confirmatory malaria diagnosis. This context provides a unique scenario to study the dynamics of pfhrp2 and pfhrp3 gene deletions without apparent RDTs selection pressure. In this study we characterized the presence of pfhrp2 and pfhrp3 genes on 325 P. falciparum samples collected in Iquitos and surrounding communities between 2011 and 2018 in order to understand the dynamics of gene deletion prevalence, potential associations with clinical symptomatology and parasite genetic background. P. falciparum presence was confirmed by microscopy and PCR of 18 s rRNA, pfmsp1 and pfmsp2. Gene deletions were assessed by amplification of exon1 and exon2 of pfhrp2 and pfhrp3 using gene specific PCRs. Confirmation of absence of HRP2 expression was assessed by ELISA of HRP2 and pLDH. Genotyping of 254 samples were performed using a panel of seven neutral microsatellite markers. Overall, pfhrp2 and pfhrp3 dual gene deletions were detected in 67% (217/324) parasite samples. Concordance between pfhrp2 deletion and negligible HRP2 protein levels was observed (Cohen's Kappa = 0.842). Prevalence of gene deletions was heterogeneous across study sites (adjusted p < 0.005) but there is an overall tendency towards increase through time in the prevalence of dual pfhrp2/3-deleted parasites between 2011 (14.3%) and 2016 (88.39%) stabilizing around 65% in 2018. Dual deletions increase was associated with dominance of a single new parasite haplotype (H8) which rapidly spread to all study sites during the 8 study years. Interestingly, participants infected with dual pfhrp2/3-deleted parasites had a significantly lower parasitemias than those without gene deletions in this cohort. Our study showed the increase of pfhrp2/3 deletions in the absence of RDTs pressure and a clonal replacement of circulating lines in the Peruvian Amazon basin. These results suggest that other factors linked to the pfhrp2/3 deletion provide a selective advantage over non-deleted strains and highlight the need for additional studies and continuing surveillance.

Epidemiology of mutant Plasmodium falciparum parasites lacking histidine-rich protein 2/3 genes in Eritrea 2 years after switching from HRP2-based RDTs.

Eritrea was the first African country to complete a nationwide switch in 2016 away from HRP2-based RDTs due to high rates of false-negative RDT results caused by Plasmodium falciparum parasites lacking hrp2/hrp3 genes. A cross-sectional survey was conducted during 2019 enrolling symptomatic malaria patients from nine health facilities across three zones consecutively to investigate the epidemiology of P. falciparum lacking hrp2/3 after the RDT switch. Molecular analyses of 715 samples revealed the overall prevalence of hrp2-, hrp3-, and dual hrp2/3-deleted parasites as 9.4% (95%CI 7.4-11.7%), 41.7% (95% CI 38.1-45.3%) and 7.6% (95% CI 5.8-9.7%), respectively. The prevalence of hrp2- and hrp3-deletion is heterogeneous within and between zones: highest in Anseba (27.1% and 57.9%), followed by Gash Barka (6.4% and 37.9%) and Debub zone (5.2% and 43.8%). hrp2/3-deleted parasites have multiple diverse haplotypes, with many shared or connected among parasites of different hrp2/3 status, indicating mutant parasites have likely evolved from multiple and local parasite genetic backgrounds. The findings show although prevalence of hrp2/3-deleted parasites is lower 2 years after RDT switching, HRP2-based RDTs remain unsuitable for malaria diagnosis in Eritrea. Continued surveillance of hrp2/3-deleted parasites in Eritrea and neighbouring countries is required to monitor the trend.

Molecular diagnosis of scabies using a novel probe-based polymerase chain reaction assay targeting high-copy number repetitive sequences in the Sarcoptes scabiei genome.

BACKGROUND: The suboptimal sensitivity and specificity of available diagnostic methods for scabies hampers clinical management, trials of new therapies and epidemiologic studies. Additionally, parasitologic diagnosis by microscopic examination of skin scrapings requires sample collection with a sharp scalpel blade, causing discomfort to patients and difficulty in children. Polymerase chain reaction (PCR)-based diagnostic assays, combined with non-invasive sampling methods, represent an attractive approach. In this study, we aimed to develop a real-time probe-based PCR test for scabies, test a non-invasive sampling method and evaluate its diagnostic performance in two clinical settings. METHODOLOGY/PRINCIPAL FINDINGS: High copy-number repetitive DNA elements were identified in draft Sarcoptes scabiei genome sequences and used as assay targets for diagnostic PCR. Two suitable repetitive DNA sequences, a 375 base pair microsatellite (SSR5) and a 606 base pair long tandem repeat (SSR6), were identified. Diagnostic sensitivity and specificity were tested using relevant positive and negative control materials and compared to a published assay targeting the mitochondrial cox1 gene. Both assays were positive at a 1:100 dilution of DNA from a single mite; no amplification was observed in DNA from samples from 19 patients with other skin conditions nor from house dust, sheep or dog mites, head and body lice or from six common skin bacterial and fungal species. Moderate sensitivity of the assays was achieved in a pilot study, detecting 5/7 (71.4% [95% CI: 29.0% - 96.3%]) of clinically diagnosed untreated scabies patients). Greater sensitivity was observed in samples collected by FLOQ swabs compared to skin scrapings. CONCLUSIONS/SIGNIFICANCE: This newly developed qPCR assay, combined with the use of an alternative non-invasive swab sampling technique offers the possibility of enhanced diagnosis of scabies. Further studies will be required to better define the diagnostic performance of these tests.

Treatment of pigs with endectocides as a complementary tool for combating malaria transmission by Anopheles farauti (s.s.) in Papua New Guinea.

BACKGROUND: Outdoor, early-biting, zoophagic behaviours by Anopheles farauti (s.s.) can compromise the effectiveness of bed nets for malaria control. In the Western Pacific region, pigs and dogs represent significant alternative blood sources for mosquitoes. Treating these animals with endectocides may impact mosquito survival and complement control measures. This hypothesis was explored using membrane feeding assays (MFAs), direct feeds on treated pigs, pharmacokinetic analyses and a transmission model. RESULTS: Ivermectin was 375-fold more mosquitocidal than moxidectin (24 h LC50 = 17.8 ng/ml vs 6.7 µg/ml) in MFAs, and reduced mosquito fecundity by > 50% at ≥ 5 ng/ml. Treatment of pigs with subcutaneous doses of 0.6 mg/kg ivermectin caused 100% mosquito mortality 8 days after administration. Lethal effects persisted for up to 15 days after administration (75% death within 10 days). CONCLUSION: The application of these empirical data to a unique malaria transmission model that used a three-host system (humans, pigs and dogs) predicts that the application of ivermectin will cause a significant reduction in the entomological inoculation rate (EIR = 100 to 0.35). However, this is contingent on local malaria vectors sourcing a significant proportion of their blood meals from pigs. This provides significant insights on the benefits of deploying endectocides alongside long-lasting insecticide-treated nets (LLINs) to address residual malaria transmission.

PCR-based assay to survey for knockdown resistance to pyrethroid acaricides in human scabies mites (Sarcoptes scabiei var hominis).

Permethrin, in the form of a topical cream, is being increasingly used for community-based programs to control endemic scabies. The development of resistance has reduced the use of pyrethroids for the control of many arthropods of economic and health importance. The best recognized form of pyrethroid resistance, known as knockdown resistance or kdr, has been linked to specific mutations in the target of these agents, the para-homologous voltage-sensitive sodium channel gene (Vssc). To develop tools to study resistance to pyrethroid acaricides, we cloned 3711 and 6151 bp, respectively, of cDNA and genomic fragments of the Vssc gene from scabies mite, Sarcoptes scabiei. The sequence encompasses the major polymorphic amino acid residues associated with pyrethroid resistance. A polymerase chain reaction-based strategy has been developed that enables genotyping individual scabies mites. This will facilitate early detection and monitoring of pyrethroid resistance in scabies mite populations under drug selection pressure.

Sensitive Detection of Plasmodium vivax Using a High-Throughput, Colourimetric Loop Mediated Isothermal Amplification (HtLAMP) Platform: A Potential Novel Tool for Malaria Elimination.

INTRODUCTION: Plasmodium vivax malaria has a wide geographic distribution and poses challenges to malaria elimination that are likely to be greater than those of P. falciparum. Diagnostic tools for P. vivax infection in non-reference laboratory settings are limited to microscopy and rapid diagnostic tests but these are unreliable at low parasitemia. The development and validation of a high-throughput and sensitive assay for P. vivax is a priority. METHODS: A high-throughput LAMP assay targeting a P. vivax mitochondrial gene and deploying colorimetric detection in a 96-well plate format was developed and evaluated in the laboratory. Diagnostic accuracy was compared against microscopy, antigen detection tests and PCR and validated in samples from malaria patients and community controls in a district hospital setting in Sabah, Malaysia. RESULTS: The high throughput LAMP-P. vivax assay (HtLAMP-Pv) performed with an estimated limit of detection of 1.4 parasites/ µL. Assay primers demonstrated cross-reactivity with P. knowlesi but not with other Plasmodium spp. Field testing of HtLAMP-Pv was conducted using 149 samples from symptomatic malaria patients (64 P. vivax, 17 P. falciparum, 56 P. knowlesi, 7 P. malariae, 1 mixed P. knowlesi/P. vivax, with 4 excluded). When compared against multiplex PCR, HtLAMP-Pv demonstrated a sensitivity for P. vivax of 95% (95% CI 87-99%); 61/64), and specificity of 100% (95% CI 86-100%); 25/25) when P. knowlesi samples were excluded. HtLAMP-Pv testing of 112 samples from asymptomatic community controls, 7 of which had submicroscopic P. vivax infections by PCR, showed a sensitivity of 71% (95% CI 29-96%; 5/7) and specificity of 93% (95% CI87-97%; 98/105). CONCLUSION: This novel HtLAMP-P. vivax assay has the potential to be a useful field applicable molecular diagnostic test for P. vivax infection in elimination settings.

The Utility of Malaria Rapid Diagnostic Tests as a Tool in Enhanced Surveillance for Malaria Elimination in Vanuatu.

BACKGROUND: As part of efforts to eliminate malaria, Vanuatu has piloted the implementation of enhanced malaria surveillance and response strategies since 2011. This involves passive case detection (PCD) in health facilities, proactive case detection (Pro-ACD) and reactive case detection (Re-ACD) in communities using malaria rapid diagnostic tests (RDTs). While RDTs improve case management, their utility for detection of malaria infections in ACDs in this setting is unclear. METHODS: The utility of malaria RDTs as diagnostic tools was evaluated in PCD, in five rounds of Pro-ACDs and five rounds of Re-ACDs conducted in Tafea and Torba Provinces between 2011 and 2014. The number of malaria infections detected by RDTs was compared to that detected by PCR from collected used-RDTs. RESULTS: PCD in Tafea Province (2013) showed a RDT-positive rate of 0.21% (2/939) and a PCR-positive rate of 0.44% (2/453), indicating less than 1% of suspected malaria cases in Tafea Province were due to malaria. In Pro-ACDs conducted in Tafea and Torba Provinces, RDT-positive rates in 2013 and 2014 were 0.14% (3/2145) and 0% (0/2823), respectively, while the corresponding PCR-positive rates were 0.72% (9/1242) and 0.79% (9/1141). PCR identified villages in both provinces appearing to be transmission foci with a small number of low-density infections, mainly P. falciparum infections. In five rounds of Re-ACD, RDTs did not identify any additional infections while PCR detected only one among 173 subjects screened. CONCLUSIONS: PCD and Pro-ACDs demonstrate that both Tafea and Torba Provinces in Vanuatu has achieved very low malaria prevalence. In these low-transmission areas, conducting Pro-ACD and Re-ACDs using RDTs appears not cost-effective and may have limited impact on interrupting malaria transmission due to the small number of infections identified by RDTs and considerable operational resources invested. More sensitive, field deployable and affordable diagnostic tools will improve malaria surveillance in malaria elimination settings.

Safety and Reproducibility of a Clinical Trial System Using Induced Blood Stage Plasmodium vivax Infection and Its Potential as a Model to Evaluate Malaria Transmission.

BACKGROUND: Interventions to interrupt transmission of malaria from humans to mosquitoes represent an appealing approach to assist malaria elimination. A limitation has been the lack of systems to test the efficacy of such interventions before proceeding to efficacy trials in the field. We have previously demonstrated the feasibility of induced blood stage malaria (IBSM) infection with Plasmodium vivax. In this study, we report further validation of the IBSM model, and its evaluation for assessment of transmission of P. vivax to Anopheles stephensi mosquitoes. METHODS: Six healthy subjects (three cohorts, n = 2 per cohort) were infected with P. vivax by inoculation with parasitized erythrocytes. Parasite growth was monitored by quantitative PCR, and gametocytemia by quantitative reverse transcriptase PCR (qRT-PCR) for the mRNA pvs25. Parasite multiplication rate (PMR) and size of inoculum were calculated by linear regression. Mosquito transmission studies were undertaken by direct and membrane feeding assays over 3 days prior to commencement of antimalarial treatment, and midguts of blood fed mosquitoes dissected and checked for presence of oocysts after 7-9 days. RESULTS: The clinical course and parasitemia were consistent across cohorts, with all subjects developing mild to moderate symptoms of malaria. No serious adverse events were reported. Asymptomatic elevated liver function tests were detected in four of six subjects; these resolved without treatment. Direct feeding of mosquitoes was well tolerated. The estimated PMR was 9.9 fold per cycle. Low prevalence of mosquito infection was observed (1.8%; n = 32/1801) from both direct (4.5%; n = 20/411) and membrane (0.9%; n = 12/1360) feeds. CONCLUSION: The P. vivax IBSM model proved safe and reliable. The clinical course and PMR were reproducible when compared with the previous study using this model. The IBSM model presented in this report shows promise as a system to test transmission-blocking interventions. Further work is required to validate transmission and increase its prevalence. TRIAL REGISTRATION: Anzctr.org.au ACTRN12613001008718.