A Prodrug Strategy to Reposition Atovaquone as a Long-Acting Injectable for Malaria Chemoprotection

Recent malaria drug discovery approaches have been extensively focused on the development of oral, smallmolecule inhibitors for disease treatment whereas parenteral routes of administration have been avoided due to limitations in deploying a shelf-stable injectable even though it could be dosed less frequently. However, an updated target candidate profile from Medicines for Malaria Venture (MMV) and stakeholders have advocated for long-acting injectable chemopreventive agents as an important interventive tool to improve malaria prevention. Here, we present strategies for the development of a long-acting, intramuscular, injectable atovaquone prophylactic therapy. We have generated three prodrug approaches that are contrasted by their differential physiochemical properties and pharmacokinetic profiles: mCBK068, a docosahexaenoic acid ester of atovaquone formulated in sesame oil, mCKX352, a heptanoic acid ester of atovaquone formulated as a solution in sesame oil, and mCBE161, an acetic acid ester of atovaquone formulated as an aqueous suspension. As a result, from a single 20 mg/kg intramuscular injection, mCKX352 and mCBE161 maintain blood plasma exposure of atovaquone above the minimal efficacious concentration for >70 days and >30 days, respectively, in cynomolgus monkeys. The differences in plasma exposure are reflective of the prodrug strategy, which imparts altered chemical properties that ultimately influence aqueous solubility and depot release kinetics. On the strength of the pharmacokinetic and safety profiles, mCBE161 is being advanced as a first-in-class clinical candidate for first-in-human trials.

Proguanil and chlorhexidine augment the antibacterial activities of clarithromycin and rifampicin against Acinetobacter baumannii

The emergence of Acinetobacter baumannii infections as a significant healthcare concern in hospital settings, coupled with their association with poorer clinical outcomes, has prompted extensive investigation into novel therapeutic agents and innovative treatment strategies. Proguanil and chlorhexidine, both categorized as biguanide compounds, have displayed clinical efficacy as antimalarial and topical antibacterial agents, respectively. In this study, we conducted an investigation to assess the effectiveness of combining proguanil and chlorhexidine with clarithromycin or rifampicin against both laboratory strains and clinical isolates of A. baumannii. The combination therapy demonstrated rapid bactericidal activity against planktonic multidrug-resistant A. baumannii, exhibiting efficacy in eradicating mature biofilms and impeding the development of antibiotic resistance in vitro. Additionally, when administered in conjunction with clarithromycin or rifampicin, proguanil enhanced the survival rate of mice afflicted with intraperitoneal A. baumannii infections, and chlorhexidine expedited wound healing in mice with skin infections. These findings are likely attributable to the disruption of A. baumannii cell membrane integrity by proguanil and chlorhexidine, resulting in heightened membrane permeability and enhanced intracellular accumulation of clarithromycin and rifampicin. Overall, this study underscores the potential of employing proguanil and chlorhexidine in combination with specific antibiotics to effectively combat A. baumannii infections and improve treatment outcomes in clinically challenging scenarios.

A Safe and Effective Atovaquone-Proguanil Therapeutic Protocol for the Treatment of Avian Malaria by Plasmodium relictum in Snowy Owl (Bubo scandiacus)

Avian malaria is a re-emerging threat to avian species worldwide. It is sustained by several protozoan species belonging to the genus Plasmodium, mainly Plasmodium relictum. The even wider diffusion of the disease, probably because of the increase in the areas covered by their mosquito vectors, may pose new risks for avian species lacking natural resistance (especially those from artic or sub-artic environments) or those hosted in structures like zoos and wildlife rescue centers. With that premise, this study describes the efficacy and safety of a therapeutic protocol to treat avian malaria in three snowy owls (Bubo scandiacus) hosted in a wildlife rescue center in Apulia, south of Italy, and affected by avian malaria by P. relictum. The protocol consisted of administering 10/4 mg/kg atovaquone/proguanil per os once a day for three consecutive days, repeating this seven days later. Seven days after the end of the treatment, P. relictum was not detected in the birds' blood and no adverse effects were observed during the 60 days of monitoring after the end of the treatment. Therefore, a therapeutic regimen of 10/4 mg/kg/day may be considered safe and effective in a valuable and endangered species such as B. scandiacus.

On the potential for discontinuing atovaquone-proguanil (AP) ad-hoc post-exposure and other abbreviated AP-regimens: Pharmacology, pharmacokinetics and perspectives

According to current guidelines, atovaquone-proguanil (AP) malaria chemoprophylaxis should be taken once daily starting one day before travel and continued for seven days post-exposure. However, drug-sparing regimens, including discontinuing AP after leaving malaria-endemic areas are cost-saving and probably more attractive to travelers, and may thus enhance adherence. AP has causal prophylactic effects, killing malaria parasites during the hepatic stage. If early hepatic stages were already targeted by AP, AP could possibly be discontinued upon return. Pharmacokinetic data and studies on drug-sparing AP regimens suggest this to be the case. Nevertheless, the evidence is weak and considered insufficient to modify current recommendations. Field trials require large numbers of travelers and inherently suffer from the lack of a control group. Safely-designed controlled human malaria infection trials could significantly reduce study participant numbers and safely establish an effective AP abbreviated regimen which we propose as the optimal trial design to test this concept.

Discontinuing atovaquone/proguanil prophylaxis ad-hoc post-exposure and during-travel dose-sparing prophylactic regimens against P. falciparum malaria: An update with pointers for future research

BACKGROUND

Atovaquone/proguanil (AP) is a highly effective malaria chemoprophylaxis combination. According to current guidelines, AP is taken once daily during, and continued for seven days post exposure. A systematic review by Savelkoel et al. summarised data up to 2017 on abbreviated AP regimens, and concluded that discontinuing AP upon return may be effective, although the available data was insufficient to modify current recommendations. The same applies to other studies evaluating during-travel dose-sparing regimens.

METHODS

A literature search in Pubmed and Embase was performed including search terms related to AP prophylaxis and pharmacokinetics to search for recent studies on abbreviated AP regimens published since 2017.

RESULTS

Since the 2017 review, no new studies assessing discontinuing AP ad-hoc post-exposure prophylaxis have been published. Two new studies were identified assessing other abbreviated AP regimens; one investigated a twice-weekly AP regimen in 32 travellers, and one a three-day AP course in therapeutic dose (1000/400 mg) prior to exposure in 215 travellers. No malaria cases were detected in the study participants adhering to these regimens.

CONCLUSIONS

Further research would be needed if the research question is considered of sufficient importance to facilitate evidence-based decision-making to modify current guidelines, as efficacy studies in travellers are fraught with confounders. We recommend human challenge trials to study abbreviated AP regimens pertaining to malaria chemoprophylaxis as they allow for rational, subject number, time- and cost-saving trial designs.

Reproducibility of malaria sporozoite challenge model in humans for evaluating efficacy of vaccines and drugs: a systematic review

BACKGROUND

The development of novel malaria vaccines and antimalarial drugs is limited partly by emerging challenges to conduct field trials in malaria endemic areas, including unknown effects of existing immunity and a reported fall in malaria incidence. As a result, Controlled Human Malaria Infection (CHMI) has become an important approach for accelerated development of malarial vaccines and drugs. We conducted a systematic review of the literature to establish aggregate evidence on the reproducibility of a malaria sporozoite challenge model.

METHODS

A systematic review of research articles published between 1990 and 2018 on efficacy testing of malaria vaccines and drugs using sporozoite challenge and sporozoite infectivity studies was conducted using Pubmed, Scopus, Embase and Cochrane Library, ClinicalTrials.gov and Trialtrove. The inclusion criteria were randomized and non-randomized, controlled or open-label trials using P. falciparum or P. vivax sporozoite challenges. The data were extracted from articles using standardized data extraction forms and descriptive analysis was performed for evidence synthesis. The endpoints considered were infectivity, prepatent period, parasitemia and safety of sporozoite challenge.

RESULTS

Seventy CHMI trials conducted with a total of 2329 adult healthy volunteers were used for analysis. CHMI was induced by bites of mosquitoes infected with P. falciparum or P. vivax in 52 trials and by direct venous inoculation of P. falciparum sporozoites (PfSPZ challenge) in 18 trials. Inoculation with P. falciparum-infected mosquitoes produced 100% infectivity in 40 studies and the mean/median prepatent period assessed by thick blood smear (TBS) microscopy was ≤ 12 days in 24 studies. On the other hand, out of 12 infectivity studies conducted using PfSPZ challenge, 100% infection rate was reproduced in 9 studies with a mean or median prepatent period of 11 to 15.3 days as assessed by TBS and 6.8 to 12.6 days by PCR. The safety profile of P. falciparum and P.vivax CHMI was characterized by consistent features of malaria infection.

CONCLUSION

There is ample evidence on consistency of P. falciparum CHMI models in terms of infectivity and safety endpoints, which supports applicability of CHMI in vaccine and drug development. PfSPZ challenge appears more feasible for African trials based on current evidence of safety and efficacy.

Liver Enzyme Elevations in Plasmodium falciparum Volunteer Infection Studies: Findings and Recommendations

Malaria volunteer infection studies (VISs) accelerate new drug and vaccine development. In the induced blood-stage malaria (IBSM) model, volunteers are inoculated with erythrocytes infected with Plasmodium falciparum. Observations of elevated liver enzymes in the IBSM model with new chemical entities (NCEs) promoted an analysis of available data. Data were reviewed from eight IBSM studies of seven different NCEs, plus two studies with the registered antimalarial piperaquine conducted between June 2013 and January 2017 at QIMR Berghofer, Brisbane, Australia. Alanine aminotransferase (ALT) was elevated (> 2.5 times the upper limit of normal [×ULN]) in 20/114 (17.5%) participants. Of these, 8.9% (10/114) had moderate increases (> 2.5–5 × ULN), noted in seven studies of six different NCEs ± piperaquine or piperaquine alone, and 8.9% (10/114) had severe elevations (> 5 × ULN), occurring in six studies of six different NCEs ± piperaquine. Aspartate aminotransferase (AST) was elevated (> 2.5 × ULN) in 11.4% (13/114) of participants, across six of the 10 studies. Bilirubin was > 2 × ULN in one participant. Published data from other VIS models, using sporozoite inoculation by systemic administration or mosquito feeding, also showed moderate/severe liver enzyme elevations. In conclusion, liver enzyme elevations in IBSM studies are most likely multifactorial and could be caused by the model conditions, that is, malaria infection/parasite density and/or effective parasite clearance, or by participant-specific risk factors, acetaminophen administration, or direct hepatotoxicity of the test drug. We make recommendations that may mitigate the risk of liver enzyme elevations in future VISs and propose measures to assist their interpretation, should they occur.

Experimental infection of human volunteers

Controlled human infection (CHI) trials, in which healthy volunteers are experimentally infected, can accelerate the development of novel drugs and vaccines for infectious diseases of global importance. The use of CHI models is expanding from around 60 studies in the 1970s to more than 120 publications in this decade, primarily for influenza, rhinovirus, and malaria. CHI trials have provided landmark data for several registered drugs and vaccines, and have generated unprecedented scientific insights. Because of their invasive nature, CHI studies demand critical ethical review according to established frameworks. CHI-associated serious adverse events are rarely reported. Novel CHI models need standardised safety data from comparable CHI models to facilitate evidence-based risk assessments, as well as funds to produce challenge inoculum according to regulatory requirements. Advances such as the principle of controlled colonisation, the expansion of models to endemic areas, and the use of genetically attenuated strains will further broaden the scope of CHI trials.

Long-acting injectable atovaquone nanomedicines for malaria prophylaxis

Chemoprophylaxis is currently the best available prevention from malaria, but its efficacy is compromised by non-adherence to medication. Here we develop a long-acting injectable formulation of atovaquone solid drug nanoparticles that confers long-lived prophylaxis against Plasmodium berghei ANKA malaria in C57BL/6 mice. Protection is obtained at plasma concentrations above 200 ng ml-1 and is causal, attributable to drug activity against liver stage parasites. Parasites that appear after subtherapeutic doses remain atovaquone-sensitive. Pharmacokinetic-pharmacodynamic analysis indicates protection can translate to humans at clinically achievable and safe drug concentrations, potentially offering protection for at least 1 month after a single administration. These findings support the use of long-acting injectable formulations as a new approach for malaria prophylaxis in travellers and for malaria control in the field.

Abbreviated atovaquone-proguanil prophylaxis regimens in travellers after leaving malaria-endemic areas: A systematic review

BACKGROUND

We evaluated existing data on the prophylactic efficacy of atovaquone-proguanil (AP) in order to determine whether prophylaxis in travellers can be discontinued on the day of return from a malaria-endemic area instead of seven days after return as per currently recommended post-travel schedule.

METHODS

PubMed and Embase databases were searched to identify relevant studies. This PROSPERO-registered systematic review followed PRISMA guidelines. The search strategy included terms or synonyms relevant to AP combined with terms to identify articles relating to prophylactic use of AP and inhibitory and half-life properties of AP. Studies considered for inclusion were: randomized controlled trials, cohort studies, quasi-experimental studies, open-label trials, patient-control studies, cross-sectional studies; as well as case-series and non-clinical studies. Data on study design, characteristics of participants, interventions, and outcomes were extracted. Primary outcomes considered relevant were prophylactic efficacy and prolonged inhibitory activity and half-life properties of AP.

RESULTS

The initial search identified 1,482 publications, of which 40 were selected based on screening. Following full text review, 32 studies were included and categorized into two groups, namely studies in support of the current post-travel regimen (with a total of 2,866 subjects) and studies in support of an alternative regimen (with a total of 533 subjects).

CONCLUSION

There is limited direct and indirect evidence to suggest that an abbreviated post-travel regimen for AP may be effective. Proguanil, however, has a short half-life and is essential for the synergistic effect of the combination. Stopping AP early may result in mono-prophylaxis with atovaquone and possibly select for atovaquone-resistant parasites. Furthermore, the quality of the studies in support of the current post-travel regimen outweighs the quality of the studies in support of an alternative short, post-travel regimen, and the total sample size of the studies to support stopping AP early comprises a small percentage of the total sample size of the studies performed to establish the efficacy of the current AP regimen. Additional research is required - especially from studies evaluating impact on malaria parasitaemia and clinical illness and conducted among travellers in high malaria risk settings - before an abbreviated regimen can be recommended in current practice.

PROSPERO REGISTRATION NUMBER

CRD42017055244.

Controlled Human Malaria Infection: Applications, Advances, and Challenges

Controlled human malaria infection (CHMI) entails deliberate infection with malaria parasites either by mosquito bite or by direct injection of sporozoites or parasitized erythrocytes. When required, the resulting blood-stage infection is curtailed by the administration of antimalarial drugs. Inducing a malaria infection via inoculation with infected blood was first used as a treatment (malariotherapy) for neurosyphilis in Europe and the United States in the early 1900s. More recently, CHMI has been applied to the fields of malaria vaccine and drug development, where it is used to evaluate products in well-controlled early-phase proof-of-concept clinical studies, thus facilitating progression of only the most promising candidates for further evaluation in areas where malaria is endemic. Controlled infections have also been used to immunize against malaria infection. Historically, CHMI studies have been restricted by the need for access to insectaries housing infected mosquitoes or suitable malaria-infected individuals. Evaluation of vaccine and drug candidates has been constrained in these studies by the availability of a limited number of Plasmodium falciparum isolates. Recent advances have included cryopreservation of sporozoites, the manufacture of well-characterized and genetically distinct cultured malaria cell banks for blood-stage infection, and the availability of Plasmodium vivax-specific reagents. These advances will help to accelerate malaria vaccine and drug development by making the reagents for CHMI more widely accessible and also enabling a more rigorous evaluation with multiple parasite strains and species. Here we discuss the different applications of CHMI, recent advances in the use of CHMI, and ongoing challenges for consideration.

Atovaquone and ELQ-300 Combination Therapy as a Novel Dual-Site Cytochrome bc1 Inhibition Strategy for Malaria

Antimalarial combination therapies play a crucial role in preventing the emergence of drug-resistant Plasmodium parasites. Although artemisinin-based combination therapies (ACTs) comprise the majority of these formulations, inhibitors of the mitochondrial cytochrome bc1 complex (cyt bc1) are among the few compounds that are effective for both acute antimalarial treatment and prophylaxis. There are two known sites for inhibition within cyt bc1: atovaquone (ATV) blocks the quinol oxidase (Qo) site of cyt bc1, while some members of the endochin-like quinolone (ELQ) family, including preclinical candidate ELQ-300, inhibit the quinone reductase (Qi) site and retain full potency against ATV-resistant Plasmodium falciparum strains with Qo site mutations. Here, we provide the first in vivo comparison of ATV, ELQ-300, and combination therapy consisting of ATV plus ELQ-300 (ATV:ELQ-300), using P. yoelii murine models of malaria. In our monotherapy assessments, we found that ATV functioned as a single-dose curative compound in suppressive tests whereas ELQ-300 demonstrated a unique cumulative dosing effect that successfully blocked recrudescence even in a high-parasitemia acute infection model. ATV:ELQ-300 therapy was highly synergistic, and the combination was curative with a single combined dose of 1 mg/kg of body weight. Compared to the ATV:proguanil (Malarone) formulation, ATV:ELQ-300 was more efficacious in multiday, acute infection models and was equally effective at blocking the emergence of ATV-resistant parasites. Ultimately, our data suggest that dual-site inhibition of cyt bc1 is a valuable strategy for antimalarial combination therapy and that Qi site inhibitors such as ELQ-300 represent valuable partner drugs for the clinically successful Qo site inhibitor ATV.

In Vitro Analysis of the Interaction between Atovaquone and Proguanil against Liver Stage Malaria Parasites

The interaction between atovaquone and proguanil has never been studied against liver stage malaria, which is the main target of this drug combination when used for chemoprevention. Using human hepatocytes lacking cytochrome P450 activity, and thus avoiding proguanil metabolizing into potent cycloguanil, we show in vitro that the atovaquone-proguanil combination synergistically inhibits the growth of rodent Plasmodium yoelii parasites. These results provide a pharmacological basis for the high efficacy of atovaquone-proguanil used as malaria chemoprevention.

The conundrum of malaria chemoprophylaxis

Alternative approaches to malaria chemoprophylaxis are discussed in light of the difficulties of executing clinical trials within limits of infection rates and ethics.

Effectiveness of twice a week prophylaxis with atovaquone-proguanil (Malarone®) in long-term travellers to West Africa

BACKGROUND

Current guidelines recommend daily dosing of atovaquone-proguanil (AP), beginning a day before travel to endemic areas and continuing for 7 days after departure. Adherence of long-term travellers to daily malaria chemoprophylaxis tends to be poor, even when residing in highly endemic malaria regions. Evidence from a volunteer challenging study suggests that non-daily, longer intervals dosing of AP provides effective protection against Plasmodium falciparum This study examines the effectiveness of twice weekly AP prophylaxis in long-term travellers to highly endemic P. falciparum areas in West Africa.

METHODS

An observational surveillance study aimed to detect prophylactic failures associated with twice weekly AP, during the years 2013-2014, among long-term expatriates in two sites in West Africa. The expatriates were divided according to the malaria prophylaxis regimen taken: AP twice weekly; mefloquine once weekly and a group refusing to take prophylaxis. Malaria events were recorded for each group. The incidence-density of malaria was calculated by dividing malaria events per number of person-months at risk.

RESULTS

Among 122 expatriates to West Africa the malaria rates were: 11.7/1000 person-months in the group with no-prophylaxis (n = 63); 2.06/1000 person-months in the 40 expatriates taking mefloquine (P = 0.006) and no cases of malaria (0/391 person-months, P = 0.01) in the twice weekly AP group (n = 33).

CONCLUSIONS

No prophylaxis failures were detected among the group of expatriates taking AP prophylaxis twice weekly compared with 11.7/1000 person-months among the no-prophylaxis group. Twice weekly AP prophylaxis may be an acceptable approach for long-term travellers who are unwilling to adhere to malaria chemoprophylaxis guidelines.

Supporting malaria elimination with 21st century antimalarial agent drug discovery

The burden of malaria has been considerably reduced over recent years. However, to achieve disease elimination, drug discovery for the next generation needs to focus on blocking disease transmission and on targeting the liver-stage forms of the parasite. Properties of the 'ideal' new antimalarial drug and the key scientific and technological advances that have led to recent progress in antimalarial drug discovery are reviewed. Using these advances, Novartis has built a robust pipeline of next-generation antimalarials. The preclinical and clinical development of two candidate drugs: KAE609 and KAF156, provide a framework for the path to breakthrough treatments that could be taking us a step closer to the vision of malaria elimination.

Design, recruitment, and microbiological considerations in human challenge studies

Since the 18th century a wealth of knowledge regarding infectious disease pathogenesis, prevention, and treatment has been accumulated from findings of infection challenges in human beings. Partly because of improvements to ethical and regulatory guidance, human challenge studies-involving the deliberate exposure of participants to infectious substances-have had a resurgence in popularity in the past few years, in particular for the assessment of vaccines. To provide an overview of the potential use of challenge models, we present historical reports and contemporary views from experts in this type of research. A range of challenge models and practical approaches to generate important data exist and are used to expedite vaccine and therapeutic development and to support public health modelling and interventions. Although human challenge studies provide a unique opportunity to address complex research questions, participant and investigator safety is paramount. To increase the collaborative effort and future success of this area of research, we recommend the development of consensus frameworks and sharing of best practices between investigators. Furthermore, standardisation of challenge procedures and regulatory guidance will help with the feasibility for using challenge models in clinical testing of new disease intervention strategies.

Effectiveness of short prophylactic course of atovaquone-proguanil in travelers to sub-saharan Africa

BACKGROUND

Current guidelines recommend continuation of atovaquone-proguanil (AP) malaria prophylaxis for 7 days after leaving Plasmodium falciparum endemic areas. Evidence from clinical studies suggests that discontinuation of AP 1 day after exposure ends may be safe and effective. Our objective was to assess the effectiveness of short-course AP prophylaxis among travelers to sub-Saharan Africa.

METHODS

To detect prophylactic failures associated with short-course AP prophylaxis discontinued 1 day after return, we conducted active surveillance during the years 2010 and 2011, by a retrospective telephone survey 1 to 6 months after travelers' return. Passive surveillance data were obtained from the Israel Ministry of Health (MOH) malaria registry.

RESULTS

Among 485 travelers to sub-Saharan Africa (cumulative exposure of 4,979 days), 421 (87%) discontinued AP 1 day after leaving the endemic region (cumulative exposure of 4,337 days). None of the 485 travelers reported malaria infection. The MOH malaria registry survey included 363 P. falciparum-infected patients during the years 2003 to 2011. The majority (n = 305; 84%) did not use any malaria prophylaxis. None of the patients had used AP (neither regular nor short course AP) for malaria prophylaxis.

CONCLUSIONS

We did not detect prophylaxis failures among a group of travelers who discontinued AP prophylaxis 1 day after leaving malaria-endemic areas. Passive surveillance in Israel did not detect any P. falciparum cases among AP users. We recommend further validation of our findings by clinical trials, prospective studies, and active surveillance in larger cohorts to assess the effectiveness of short-course AP prophylaxis in travelers.

Multiplex 5' nuclease quantitative real-time PCR for clinical diagnosis of malaria and species-level identification and epidemiologic evaluation of malaria-causing parasites, including Plasmodium knowlesi

Molecular diagnosis of malaria offers many potential advantages over microscopy, including identification of malaria to the species level in an era with few experienced microscopists. We developed high-throughput multiplex 5' nuclease quantitative PCR (qPCR) assays, with the potential to support large studies, to specifically identify Plasmodium falciparum, P. vivax, P. ovale, P. malariae, and P. knowlesi. We compared qPCR to microscopy and confirmed discordant results with an alternative target PCR assay. The assays specifically detected 1 to 6 parasites/μl of blood. The clinical sensitivities (95% confidence intervals [CIs]) of the 4-plex assay to detect microscopically confirmed malaria were 95.8% (88.3 to 99.1%) for P. falciparum, 89.5% (75.2 to 97.1%) for P. vivax, 94.1% (71.3 to 99.9%) for P. ovale, and 100% (66.4 to 100%) for P. malariae. The specificities (95% CIs) were 98.6% (92.4 to 100%) for P. falciparum, 99% (84.8 to 100%) for P. vivax, 98.4% (94.4 to 99.8%) for P. ovale, and 99.3% (95.9 to 100%) for P. malariae. The clinical specificity for samples without malaria was 100%. The clinical sensitivity of the 5-plex assay for confirmed P. knowlesi malaria was 100% (95% CI, 69.2 to 100%), and the clinical specificity was 100% (95% CI, 87.2 to 100%). Coded retesting and testing with an alternative target PCR assay showed improved sensitivity and specificity of multiplex qPCR versus microscopy. Additionally, 91.7% (11/12) of the samples with uncertain species by microscopy were identified to the species level identically by both our multiplex qPCR assay and the alternative target PCR assay, including 9 P. falciparum infections. Multiplex qPCR can rapidly and simultaneously identify all 5 Plasmodium species known to cause malaria in humans, and it offers an alternative or adjunct to microscopy for clinical diagnosis as well as a needed high-throughput tool for research.

Experimentally induced blood stage malaria infection as a tool for clinical research

A system for experimentally induced blood stage malaria infection (IBSM) with Plasmodium falciparum by direct intravenous inoculation of infected erythrocytes was developed at the Queensland Institute of Medical Research (QIMR) more than 15 years ago. Since that time, this system has been used in several studies to investigate the protective effect of vaccines, the clearance kinetics of parasites following drug treatment, and to improve understanding of the early events in blood stage infection. In this article, we will review the development of IBSM and the applications for which it is being employed. We will discuss the advantages and disadvantages of IBSM, and finish by describing some exciting new areas of research that have been made possible by this system.

Prophylaxis of malaria

Malaria prevention in travelers to endemic areas remains dependent principally on chemoprophylaxis. Although malaria chemoprophylaxis refers to all malaria species, a distinction should be drawn between falciparum malaria prophylaxis and the prophylaxis of the relapsing malaria species (vivax & ovale). While the emergence of drug resistant strains, as well as the costs and adverse reactions to medications, complicate falciparum prophylaxis use, there are virtually no drugs available for vivax prophylaxis, beside of primaquine.Based on traveler's malaria data, a revised recommendation for using chemoprophylaxis in low risk areas should be considered.