- Email: [email protected]
Monitoring antimalarial resistance: launching a cooperative effort
Update transcends pre-erythrocytic and blood stages, because CQ arrests the life cycle at the first generation of the blood stage, in contrast to the irradiated sporozoite inoculation where the life cycle is arrested at the liver stage (Figure 1a), and so specificity is more limited. A strategy for malaria control that has similarities to this study is intermittent preventive drug treatment [13]. This involves the administration of anti-malarial drugs to at-risk individuals in endemic regions, and appears to allow the generation of immunity while removing the risk of individuals developing life-threatening disease, and avoids ‘rebound’ effects. These immune responses, however, have yet to be characterised. Furthermore, in the field, the strain of an immunizing parasite can differ from that subsequently challenging an individual following discontinuation of the drug, and immune responses might be directed to polymorphic regions of antigens. Nevertheless, the findings from these efficacious approaches reinforce one another, and so the further study of these approaches in the context of a better understanding of parasite dynamics and disease incidence in the field is highly warranted [14]. In particular, it would be essential to establish whether individuals with previous malaria exposure and disease history could still develop protective immunity, or whether their specific anti-malaria immunity is compromised. Knowing the minimum number of bites required to generate sterilizing immunity would be very valuable. Also, do the various anti-malaria drugs in use lend themselves to this immunization process? This study also lends support to the concept of generating protective immunity through infection with genetically attenuated strains of Plasmodium [15], but the issue of producing and deploying such an approach remains. It appears that the human immune system can tackle malaria through natural immunization, but needs a ‘helping hand’ from drugs to allow the more rapid, disease-free
Trends in Parasitology
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and immune suppression-free development of immunity, particularly in non-immune children who are most at risk. References 1 Roestenberg, M. et al. (2009) Protection against a malaria challenge by sporozoite inoculation. N. Engl. J. Med. 361, 468–477 2 Todryk, S.M. et al. (2008) Correlation of memory T cell responses against TRAP with protection from clinical malaria, and CD4+ CD25high T cells with susceptibility in Kenyans. PLoS ONE 3, e2027 3 Boutlis, C.S. et al. (2006) Malaria tolerance–for whom the cell tolls? Trends Parasitol. 22, 371–377 4 Wykes, M.N. and Good, M.F. (2008) What really happens to dendritic cells during malaria? Nat. Rev. Microbiol. 6, 864–870 5 Bejon, P. et al. (2007) The induction and persistence of T cell IFNgamma responses after vaccination or natural exposure is suppressed by Plasmodium falciparum. J. Immunol. 179, 4193–4201 6 Hoffman, S.L. et al. (2002) Protection of humans against malaria by immunization with radiation-attenuated Plasmodium falciparum sporozoites. J. Infect. Dis. 185, 1155–1164 7 Ballou, W.R. (2009) The development of the RTS,S malaria vaccine candidate: challenges and lessons. Parasite Immunol. 31, 492–500 8 Todryk, S.M. and Hill, A.V. (2007) Malaria vaccines: the stage we are at. Nat. Rev. Microbiol. 5, 487–489 9 Belnoue, E. et al. (2004) Protective T cell immunity against malaria liver stage after vaccination with live sporozoites under chloroquine treatment. J. Immunol. 172, 2487–2495 10 Putrianti, E.D. et al. (2009) Vaccine-like immunity against malaria by repeated causal-prophylactic treatment of liver-stage Plasmodium parasites. J. Infect. Dis. 199, 899–903 11 Robert, V. et al. (2003) Malaria transmission in urban sub-Saharan Africa. Am. J. Trop. Med. Hyg. 68, 169–176 12 O’Meara, W.P. et al. (2008) Effect of a fall in malaria transmission on morbidity and mortality in Kilifi, Kenya. Lancet 372, 1555–1562 13 Gosling, R.D. et al. (2009) Intermittent preventive treatment of malaria in infants: how does it work and where will it work? Trop. Med. Int. Health 14, 1003–1010 14 Todryk, S. and Bejon, P. (2009) Malaria vaccine development: lessons from the field. Eur. J. Immunol. 39, 2007–2010 15 Vaughan, A.M. et al. (2010) Genetically engineered, attenuated wholecell vaccine approaches for malaria. Hum. Vaccine 6, 107–113 1471-4922/$ – see front matter ß 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.pt.2010.02.003 Available online 26 February 2010
Research Focus
Monitoring antimalarial resistance: launching a cooperative effort Carol Hopkins Sibley1,2, Philippe J. Guerin2 and Pascal Ringwald3 1
Department of Genome Sciences, University of Washington, Seattle, WA, USA WorldWide Antimalarial Resistance Network, Centre for Tropical Medicine, University of Oxford, UK 3 Global Malaria Program, World Health Organization, Geneva, Switzerland 2
Current information on efficacy of antimalarials is crucial to provide early warning of resistance. A collaborative effort between the Global Malaria Program of the World Health Organization (WHO) and the WorldWide Antimalarial Resistance Network (WWARN) has recently been launched. The effort is planned as a collaboration with the scientific malaria community to create a global, comprehensive, and inclusive network that will provide qualityassured information on antimalarial drug resistance. Corresponding author: Sibley, C.H. ([email protected]).
Tools for controlling malaria Currently, control of malaria relies on prevention of infection through vector-control measures, and diagnosis and chemotherapy of cases. Providing a vaccine has proved to be a formidable challenge. In this situation, availability and appropriate use of effective antimalarial drugs is crucial, as has been demonstrated worldwide in recent decades. Plasmodium falciparum evolved resistance first to the antimalarial, chloroquine (CQ) and later to sulfadoxine–pyrimethamine (SP), and deaths from malaria among children in Africa increased markedly as a con221
Update
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Table 1. Some selected recent WHO publications with specific guidelines related to antimalarial drug treatment, assessment, and resistance Title of WHO publication Susceptibility of P. falciparum to antimalarial drugs. Report on global monitoring: 1996–2004
URL of website where publication can be viewed or downloaded as a pdf http://www.who.int/malaria/publications/atoz/whohtmmal20051103/en/
Guidelines for the treatment of malaria, 2006
http://www.who.int/malaria/publications/atoz/9241546948/en/index.html
Field application of in vitro assays for the sensitivity of human malaria parasites to antimalarial drugs, 2007
http://www.who.int/malaria/publications/atoz/9789241595155/en/
Methods and techniques for clinical trials on antimalarial drug efficacy: genotyping to identify parasite populations, 2008
http://www.who.int/malaria/publications/atoz/9789241596305/en/
Global malaria control and elimination: report of a technical review, 2008
http://www.who.int/malaria/publications/atoz/9789241596305/en/
Methods for surveillance of antimalarial drug efficacy, 2009
http://www.who.int/malaria/docs/drugresistance/Protocol2009.pdf
Malaria case management, 2009
http://www.who.int/malaria/publications/atoz/9789241598088/en/index.html
World Malaria Report, 2009
http://www.who.int/malaria/world_malaria_report_2009/en/index.html
Malaria Microscopy Quality Assurance Manual, Version 1
http://www.who.int/malaria/publications/atoz/mmicroscopy_qam/en/index.html
sequence [1,2]. In an attempt to counter the development of resistance the WHO treatment guidelines for P. falciparum now recommend artemisinin combination therapies (ACTs) that include compounds derived from artemisinin and a partner drug with a longer half-life, such as lumefantrine, mefloquine, amodiaquine, SP or piperaquine. ACTs are still clinically effective against P. falciparum wherever they have been deployed, but there are clear signs that the parasites in Western Cambodia are losing their susceptibility to the artemisinin component [3]. This history of drug resistance to the ‘old’ drugs, and the potential for resistance to evolve to ACTs, demonstrate that up-to-date information on efficacy of antimalarials is crucial to provide early warning of the development of resistance. This evidence is needed to allow policy makers to propose strategies to sustain maximally the useful therapeutic life of ACTs. Drug choice Drug efficacy varies enormously within the malaria endemic regions. Clinical assessments of antimalarial efficacy are a fundamental part of national malaria control programs. The WHO co-ordinates in vivo studies, and publishes frequently updated guidelines for treatment and for organizing and analyzing the studies (Table 1 lists some of the recent WHO publications relevant to antimalarial treatment). The information from efficacy studies is then collated with the goal of generating the evidence on which local, regional or international decisions on drug choice can be made (http://www.who.int/malaria/publications/atoz/whohtmmal 20051103/en/). Data management In recent years there have been substantial increases in the scientific, technical and economic resources focused on malaria control, and even elimination [4]. These changes provide a real opportunity to build on the current systems for assessment of antimalarial efficacy, and ensure that the information is available to policy makers in a timely and useful manner. In this spirit, the Bill & Melinda Gates Foundation has recently funded grants to support a collaborative effort between the Global Malaria Programme of 222
the WHO (http://www.gatesfoundation.org/Grants-2009/ Pages/World-Health-Organization-OPP51936.aspx) and a newly organized project based at the University of Oxford, UK – the WorldWide Antimalarial Resistance Network (WWARN) (http://www.gatesfoundation.org/Grants-2009/ Pages/University-of-Oxford-OPP48807_01.aspx). The effort represents a collaboration with the malaria scientific community to create a global, comprehensive, and inclusive network that will provide quality-assured information on antimalarial drug resistance [5–10]. A database comprising individual patient records will be developed by WWARN, with the goal of allowing comprehensive analysis of data from studies completed at different times and locations. In the context of the grant, the WHO will provide support to some countries for data collection by national programs. In addition, the WHO will, on a pilot basis (and subject always to individual countries giving their consent to the transfer of data), facilitate the transfer of in vivo individual patient data from countries to WWARN for inclusion in the Project repository. Location of data sources will be identified as points on maps that will show the overall outcome of treatment trials or other analyses. Individual data will not be accessible except to the contributor, but summary data will be publically available. Freely available tools for data management and analysis will be a major focus of the early database development (due in Spring, 2010), to facilitate the work of scientists collecting data on all aspects of antimalarial efficacy. The aggregated data in the database will be searchable so that users will be able to tailor the output to their particular needs. The first phase of the database can be accessed at http://www.wwarn.org. How is this effort different from the past? A major difference from earlier compilations of treatment efficacy is that individual patient data, rather than study summaries, will now be entered in the database, allowing analysis of information from different studies to be compared directly. Clinical assessment of drug-treatment efficacy will remain the ‘gold standard’ for evaluation of drug efficacy –when patients are treated with an antimalarial, do they recover quickly with no return of those parasites for
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Table 2. Specific goals and activities of WWARN modules WWARN Module All modules
Key outputs and activities Cooperation with and technical support for data collectors in public, private and research sectors Analysis of resistance trends across modules, regions and times Dissemination of evidence on drug resistance to all interested groups
Informatics (integrated with information from all modules)
Overall database design including security and patient privacy Online and downloadable tools useful to those collecting data Automatic system for submission of database including information on: Ethical clearance Study design Patient population Time and place of study Customized outputs, including maps, to present analyzed information to specific audiences: National, regional and international policy makers Researchers Media and public
Clinical
Technical support to data collection groups for study planning and statistical analysis Provision of suggested tools for data management and standardized analysis: Parasite clearance time Treatment outcome with survival analysis Comparison by PCR of parasite genotypes
Pharmacology
QA/QC central system for provision of reference standards for drugs and metabolites Design of analytical procedures for: Assay of drug quality and quantity Determination of levels of drug in patient samples Models of pharmacokinetic and pharmacodynamic parameters in specific patient groups
In vitro
Provision of validated drugs for in vitro analysis (with quality assurance/quality control module) Provision of genetically validated 3D7 clones for in vitro standard (with the molecular module) Development of procedures for determination of: Susceptibility of fresh patient isolates to antimalarials IC50 and IC90 inhibitory concentrations of patient isolates relative to control strain 3D7 Coordination with the molecular module to define molecular markers of drug susceptibility
Molecular markers
Provision of DNA samples with known resistance alleles as reference standards Development and dissemination of procedures for genotyping isolates at known resistance markers: P. falciparum: pfcrt, pfmdr1, dhfr, dhps, msp-1, msp-2, GLURP, microsatellites P. vivax: dhfr, dhps, msp-3a, microsatellites Coordination of platform for identification and validation of markers for resistance to artemisinins and other drugs as they are introduced
at least 28 or 42 days [an adequate clinical and parasitological response (ACPR);http://apps.who.int/malaria/docs/ drugresistance/Protocol2009.pdf]? This is a key metric because the WHO recommends that alternative treatments should be considered when fewer than 90% of patients meet the ACPR standard. In addition, another clinical parameter, the parasite clearance at Day 3 after treatment, is emerging as a useful indicator of the efficacy of the artemisinin component of ACTs (http://www.statssa. gov.za/isi2009/ScientificProgramme/IPMS/0607.pdf). Despite their importance, clinical studies are complex, timeconsuming and expensive, and this reality limits the number and power of studies that can be completed. For that reason, the WWARN database will combine data collected on clinical responses with laboratory-based approaches (Table 2). For example, treatment failure does not always stem from resistant parasites; a patient could fail treatment because the drug never attained the required level in the patient’s blood or was eliminated too rapidly to clear the parasites completely [11]. Therefore, pharmacological assessment of drug levels in patients will be included whenever possible to assess whether treatment failure did not simply reflect inadequate drug dosage or absorption. Two other approaches for monitoring drug resistance will also be included in the database. First, genetic analysis of parasites has identified molecular markers associated
with parasite resistance to some antimalarials: CQ, SP, mefloquine, amodiaquine [12] and, possibly, lumefantrine [13–16]. These markers provide a very convenient and costeffective tool for monitoring changes in the prevalence of drug-resistant parasites. An increasing prevalence of alleles of genes known to confer resistance to a drug can also provide early warning of developing resistance [17]. Equally, a decrease in ‘resistant alleles’ can be an indication of returning sensitivity when a drug is withdrawn [17]. Second, parasites can be isolated from infected patients, and the responses to drugs of those parasites can be monitored in vitro [18]. These in vitro assays allow evaluation of the susceptibility of the parasites to additional drugs not currently in use in that location. Moreover, this method allows separate assessment of parasite responses to each component of a combination drug, a particular advantage when combinations such as ACTs are of such current importance. In vitro analysis is useful because decreasing susceptibility of parasites to a drug in use is one potential early warning that resistance could be increasing in that region [19]. So far, the relationship between molecular markers and in vitro drug sensitivity on one hand, and therapeutic efficacy on the other hand, is neither linear nor completely understood. Previous reports have focused mostly on the clinical outcome of drug treatment, but the WWARN project will include 223
Update all types of information for gauging antimalarial resistance (i.e. clinical, three-day parasite clearance, in vitro data, molecular and genetic means, and pharmacological data), linking clinical and pharmacological data from an individual patient and his/her parasites, whenever possible. This approach allows far greater scope for appropriate pooling and analysis of information gathered at different times and places, comparisons that are not possible when only summaries or aggregated data from the studies are available [20]. These wider comparisons have the potential to detect subtle signs of decreasing drug efficacy, and this evidence can then be communicated to policy makers to allow strategies for containment to be devised and implemented. Integration of WWARN into current antimalarial resistance activities WHO and WWARN will have complementary roles in the collation of the information. WHO has a responsibility to assist countries in the surveillance of antimalarial drug efficacy through established relationships with the National Malaria Control Programs (NMCP) in malariaendemic countries. The WHO also supports regional networks for the co-ordination of these activities, and these networks will also have an important role [21]. WWARN will focus on the development of the database itself through collaboration with the many other organizations that collect drug– efficacy information (reviewed in Ref. [12]) and will integrate data from these organizations to provide an inclusive database. The provision of new tools can support high-quality studies and data analysis, and will aid those who do the hard work of data collection, encouraging timely sharing of the data by publication and submission to the database. Both WHO and WWARN will be involved in sharing the combined data, analyzing trends and producing the evidence needed to assess drug efficacy on a worldwide basis. The goal of this cooperative effort is to design a system that will improve the overall quality of the data collected, analyze the collated data effectively and produce analyses that are accessible, informative and useful to all those involved in antimalarial drug deployment and use. The useful life of ACTs and other drugs that are in development must be prolonged, and the data-sharing effort can certainly play an important role [22]. Acknowledgements The World Health Organization has granted the publisher permission for the reproduction of this article; ß2010. World Health Organization. Published by Elsevier Ltd. All rights reserved. The authors gratefully acknowledge the support of the Bill & Melinda Gates Foundation. P.R. is a staff member of the World Health Organization (WHO). The author alone is responsible for the views expressed in this publication and they do not necessarily represent the decisions, policy or views of the WHO.
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References 1 Trape, J.F. (2001) The public health impact of chloroquine resistance in Africa. Am. J. Trop. Med. Hyg. 64, 12–17 2 Trape, J.F. et al. (1998) Impact of chloroquine resistance on malaria mortality. C. R. Acad. Sci. III 321, 689–697 3 Dondorp, A.M. et al. (2009) Artemisinin resistance in Plasmodium falciparum malaria. N. Engl. J. Med. 361, 455–467 4 Guerin, P.J. et al. (2009) Global resistance surveillance: ensuring antimalarial efficacy in the future. Curr. Opin. Infect. Dis. 22, 593– 600 5 Bacon, D.J. et al. (2007) World Antimalarial Resistance Network (WARN). II. In vitro antimalarial drug susceptibility. Malar. J. 6, 120 6 Barnes, K.I. et al. (2007) World Antimalarial Resistance Network (WARN). IV. Clinical pharmacology. Malar. J. 6, 122 7 Plowe, C.V. et al. (2007) World Antimalarial Resistance Network (WARN). III. Molecular markers for drug resistant malaria. Malar. J. 6, 121 8 Price, R.N. et al. (2007) World Antimalarial Resistance Network (WARN). I. Clinical efficacy of antimalarial therapy. Malar. J. 6, 119 9 Sibley, C.H. et al. (2007) The rationale and plan for creating a World Antimalarial Resistance Drug Network (WARN). Malar. J. 6, 118 10 Sibley, C.H. et al. (2008) A network to monitor antimalarial drug resistance: a plan for moving forward. Trends Parasitol. 24, 43–48 11 Barnes, K.I. et al. (2008) Antimalarial dosing regimens and drug resistance. Trends Parasitol. 24, 127–134 12 Laufer, M.K. et al. (2007) Monitoring and deterring drug-resistant malaria in the era of combination therapy. Am. J. Trop. Med. Hyg. 77, 160–169 13 Dokomajilar, C. et al. (2006) Selection of Plasmodium falciparum pfmdr1 alleles following therapy with artemether–lumefantrine in an area of Uganda where malaria is highly endemic. Antimicrob. Agents Chemother. 50, 1893–1895 14 Sisowath, C. et al. (2007) The role of pfmdr1 in Plasmodium falciparum tolerance to artemether–lumefantrine in Africa. Trop. Med. Int. Health. 12, 736–742 15 Sisowath, C. et al. (2005) In vivo selection of Plasmodium falciparum pfmdr1 86N coding alleles by artemether–lumefantrine (Coartem). J. Infect. Dis. 191, 1014–1017 16 Humphreys, G.S. et al. (2007) Amodiaquine and artemether– lumefantrine select distinct alleles of the Plasmodium falciparum mdr1 gene in Tanzanian children treated for uncomplicated talaria. Antimicrob. Agents Chemother. 51, 991–997 17 Kublin, J.G. et al. (2003) Reemergence of chloroquine-sensitive Plasmodium falciparum malaria after cessation of chloroquine use in Malawi. J. Infect. Dis. 187, 1870–1875 18 Basco, L.K. (2007) Field Application of In Vitro Assays for the Sensitivity of Human Malaria Parasites to Antimalarial Drugs. World Health Organization 19 Carrara, V.I. et al. (2009) Changes in the treatment responses to artesunate–mefloquine on the northwestern border of Thailand during 13 years of continuous deployment. PLoS ONE 4, e4551 20 Zwang, J. et al. (2009) Efficacy of artesunate–amodiaquine for treating uncomplicated P. falciparum malaria in sub-Saharan Africa: a multicentre analysis. Malar. J. 8, 203 21 Sibley, C.H. and Ringwald, P. (2006) A database of antimalarial drug resistance. Malar. J. 5, 48–56 22 Kleppner, D. and Sharp, P.A. (2009) Research data in the digital age. Science 325, 368 1471-4922/$ – see front matterß 2010 World Health Organization. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.pt.2010.02.008 Available online 20 March 2010
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and immune suppression-free development of immunity, particularly in non-immune children who are most at risk. References 1 Roestenberg, M. et al. (2009) Protection against a malaria challenge by sporozoite inoculation. N. Engl. J. Med. 361, 468–477 2 Todryk, S.M. et al. (2008) Correlation of memory T cell responses against TRAP with protection from clinical malaria, and CD4+ CD25high T cells with susceptibility in Kenyans. PLoS ONE 3, e2027 3 Boutlis, C.S. et al. (2006) Malaria tolerance–for whom the cell tolls? Trends Parasitol. 22, 371–377 4 Wykes, M.N. and Good, M.F. (2008) What really happens to dendritic cells during malaria? Nat. Rev. Microbiol. 6, 864–870 5 Bejon, P. et al. (2007) The induction and persistence of T cell IFNgamma responses after vaccination or natural exposure is suppressed by Plasmodium falciparum. J. Immunol. 179, 4193–4201 6 Hoffman, S.L. et al. (2002) Protection of humans against malaria by immunization with radiation-attenuated Plasmodium falciparum sporozoites. J. Infect. Dis. 185, 1155–1164 7 Ballou, W.R. (2009) The development of the RTS,S malaria vaccine candidate: challenges and lessons. Parasite Immunol. 31, 492–500 8 Todryk, S.M. and Hill, A.V. (2007) Malaria vaccines: the stage we are at. Nat. Rev. Microbiol. 5, 487–489 9 Belnoue, E. et al. (2004) Protective T cell immunity against malaria liver stage after vaccination with live sporozoites under chloroquine treatment. J. Immunol. 172, 2487–2495 10 Putrianti, E.D. et al. (2009) Vaccine-like immunity against malaria by repeated causal-prophylactic treatment of liver-stage Plasmodium parasites. J. Infect. Dis. 199, 899–903 11 Robert, V. et al. (2003) Malaria transmission in urban sub-Saharan Africa. Am. J. Trop. Med. Hyg. 68, 169–176 12 O’Meara, W.P. et al. (2008) Effect of a fall in malaria transmission on morbidity and mortality in Kilifi, Kenya. Lancet 372, 1555–1562 13 Gosling, R.D. et al. (2009) Intermittent preventive treatment of malaria in infants: how does it work and where will it work? Trop. Med. Int. Health 14, 1003–1010 14 Todryk, S. and Bejon, P. (2009) Malaria vaccine development: lessons from the field. Eur. J. Immunol. 39, 2007–2010 15 Vaughan, A.M. et al. (2010) Genetically engineered, attenuated wholecell vaccine approaches for malaria. Hum. Vaccine 6, 107–113 1471-4922/$ – see front matter ß 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.pt.2010.02.003 Available online 26 February 2010
Research Focus
Monitoring antimalarial resistance: launching a cooperative effort Carol Hopkins Sibley1,2, Philippe J. Guerin2 and Pascal Ringwald3 1
Department of Genome Sciences, University of Washington, Seattle, WA, USA WorldWide Antimalarial Resistance Network, Centre for Tropical Medicine, University of Oxford, UK 3 Global Malaria Program, World Health Organization, Geneva, Switzerland 2
Current information on efficacy of antimalarials is crucial to provide early warning of resistance. A collaborative effort between the Global Malaria Program of the World Health Organization (WHO) and the WorldWide Antimalarial Resistance Network (WWARN) has recently been launched. The effort is planned as a collaboration with the scientific malaria community to create a global, comprehensive, and inclusive network that will provide qualityassured information on antimalarial drug resistance. Corresponding author: Sibley, C.H. ([email protected]).
Tools for controlling malaria Currently, control of malaria relies on prevention of infection through vector-control measures, and diagnosis and chemotherapy of cases. Providing a vaccine has proved to be a formidable challenge. In this situation, availability and appropriate use of effective antimalarial drugs is crucial, as has been demonstrated worldwide in recent decades. Plasmodium falciparum evolved resistance first to the antimalarial, chloroquine (CQ) and later to sulfadoxine–pyrimethamine (SP), and deaths from malaria among children in Africa increased markedly as a con221
Update
Trends in Parasitology Vol.26 No.5
Table 1. Some selected recent WHO publications with specific guidelines related to antimalarial drug treatment, assessment, and resistance Title of WHO publication Susceptibility of P. falciparum to antimalarial drugs. Report on global monitoring: 1996–2004
URL of website where publication can be viewed or downloaded as a pdf http://www.who.int/malaria/publications/atoz/whohtmmal20051103/en/
Guidelines for the treatment of malaria, 2006
http://www.who.int/malaria/publications/atoz/9241546948/en/index.html
Field application of in vitro assays for the sensitivity of human malaria parasites to antimalarial drugs, 2007
http://www.who.int/malaria/publications/atoz/9789241595155/en/
Methods and techniques for clinical trials on antimalarial drug efficacy: genotyping to identify parasite populations, 2008
http://www.who.int/malaria/publications/atoz/9789241596305/en/
Global malaria control and elimination: report of a technical review, 2008
http://www.who.int/malaria/publications/atoz/9789241596305/en/
Methods for surveillance of antimalarial drug efficacy, 2009
http://www.who.int/malaria/docs/drugresistance/Protocol2009.pdf
Malaria case management, 2009
http://www.who.int/malaria/publications/atoz/9789241598088/en/index.html
World Malaria Report, 2009
http://www.who.int/malaria/world_malaria_report_2009/en/index.html
Malaria Microscopy Quality Assurance Manual, Version 1
http://www.who.int/malaria/publications/atoz/mmicroscopy_qam/en/index.html
sequence [1,2]. In an attempt to counter the development of resistance the WHO treatment guidelines for P. falciparum now recommend artemisinin combination therapies (ACTs) that include compounds derived from artemisinin and a partner drug with a longer half-life, such as lumefantrine, mefloquine, amodiaquine, SP or piperaquine. ACTs are still clinically effective against P. falciparum wherever they have been deployed, but there are clear signs that the parasites in Western Cambodia are losing their susceptibility to the artemisinin component [3]. This history of drug resistance to the ‘old’ drugs, and the potential for resistance to evolve to ACTs, demonstrate that up-to-date information on efficacy of antimalarials is crucial to provide early warning of the development of resistance. This evidence is needed to allow policy makers to propose strategies to sustain maximally the useful therapeutic life of ACTs. Drug choice Drug efficacy varies enormously within the malaria endemic regions. Clinical assessments of antimalarial efficacy are a fundamental part of national malaria control programs. The WHO co-ordinates in vivo studies, and publishes frequently updated guidelines for treatment and for organizing and analyzing the studies (Table 1 lists some of the recent WHO publications relevant to antimalarial treatment). The information from efficacy studies is then collated with the goal of generating the evidence on which local, regional or international decisions on drug choice can be made (http://www.who.int/malaria/publications/atoz/whohtmmal 20051103/en/). Data management In recent years there have been substantial increases in the scientific, technical and economic resources focused on malaria control, and even elimination [4]. These changes provide a real opportunity to build on the current systems for assessment of antimalarial efficacy, and ensure that the information is available to policy makers in a timely and useful manner. In this spirit, the Bill & Melinda Gates Foundation has recently funded grants to support a collaborative effort between the Global Malaria Programme of 222
the WHO (http://www.gatesfoundation.org/Grants-2009/ Pages/World-Health-Organization-OPP51936.aspx) and a newly organized project based at the University of Oxford, UK – the WorldWide Antimalarial Resistance Network (WWARN) (http://www.gatesfoundation.org/Grants-2009/ Pages/University-of-Oxford-OPP48807_01.aspx). The effort represents a collaboration with the malaria scientific community to create a global, comprehensive, and inclusive network that will provide quality-assured information on antimalarial drug resistance [5–10]. A database comprising individual patient records will be developed by WWARN, with the goal of allowing comprehensive analysis of data from studies completed at different times and locations. In the context of the grant, the WHO will provide support to some countries for data collection by national programs. In addition, the WHO will, on a pilot basis (and subject always to individual countries giving their consent to the transfer of data), facilitate the transfer of in vivo individual patient data from countries to WWARN for inclusion in the Project repository. Location of data sources will be identified as points on maps that will show the overall outcome of treatment trials or other analyses. Individual data will not be accessible except to the contributor, but summary data will be publically available. Freely available tools for data management and analysis will be a major focus of the early database development (due in Spring, 2010), to facilitate the work of scientists collecting data on all aspects of antimalarial efficacy. The aggregated data in the database will be searchable so that users will be able to tailor the output to their particular needs. The first phase of the database can be accessed at http://www.wwarn.org. How is this effort different from the past? A major difference from earlier compilations of treatment efficacy is that individual patient data, rather than study summaries, will now be entered in the database, allowing analysis of information from different studies to be compared directly. Clinical assessment of drug-treatment efficacy will remain the ‘gold standard’ for evaluation of drug efficacy –when patients are treated with an antimalarial, do they recover quickly with no return of those parasites for
Update
Trends in Parasitology
Vol.26 No.5
Table 2. Specific goals and activities of WWARN modules WWARN Module All modules
Key outputs and activities Cooperation with and technical support for data collectors in public, private and research sectors Analysis of resistance trends across modules, regions and times Dissemination of evidence on drug resistance to all interested groups
Informatics (integrated with information from all modules)
Overall database design including security and patient privacy Online and downloadable tools useful to those collecting data Automatic system for submission of database including information on: Ethical clearance Study design Patient population Time and place of study Customized outputs, including maps, to present analyzed information to specific audiences: National, regional and international policy makers Researchers Media and public
Clinical
Technical support to data collection groups for study planning and statistical analysis Provision of suggested tools for data management and standardized analysis: Parasite clearance time Treatment outcome with survival analysis Comparison by PCR of parasite genotypes
Pharmacology
QA/QC central system for provision of reference standards for drugs and metabolites Design of analytical procedures for: Assay of drug quality and quantity Determination of levels of drug in patient samples Models of pharmacokinetic and pharmacodynamic parameters in specific patient groups
In vitro
Provision of validated drugs for in vitro analysis (with quality assurance/quality control module) Provision of genetically validated 3D7 clones for in vitro standard (with the molecular module) Development of procedures for determination of: Susceptibility of fresh patient isolates to antimalarials IC50 and IC90 inhibitory concentrations of patient isolates relative to control strain 3D7 Coordination with the molecular module to define molecular markers of drug susceptibility
Molecular markers
Provision of DNA samples with known resistance alleles as reference standards Development and dissemination of procedures for genotyping isolates at known resistance markers: P. falciparum: pfcrt, pfmdr1, dhfr, dhps, msp-1, msp-2, GLURP, microsatellites P. vivax: dhfr, dhps, msp-3a, microsatellites Coordination of platform for identification and validation of markers for resistance to artemisinins and other drugs as they are introduced
at least 28 or 42 days [an adequate clinical and parasitological response (ACPR);http://apps.who.int/malaria/docs/ drugresistance/Protocol2009.pdf]? This is a key metric because the WHO recommends that alternative treatments should be considered when fewer than 90% of patients meet the ACPR standard. In addition, another clinical parameter, the parasite clearance at Day 3 after treatment, is emerging as a useful indicator of the efficacy of the artemisinin component of ACTs (http://www.statssa. gov.za/isi2009/ScientificProgramme/IPMS/0607.pdf). Despite their importance, clinical studies are complex, timeconsuming and expensive, and this reality limits the number and power of studies that can be completed. For that reason, the WWARN database will combine data collected on clinical responses with laboratory-based approaches (Table 2). For example, treatment failure does not always stem from resistant parasites; a patient could fail treatment because the drug never attained the required level in the patient’s blood or was eliminated too rapidly to clear the parasites completely [11]. Therefore, pharmacological assessment of drug levels in patients will be included whenever possible to assess whether treatment failure did not simply reflect inadequate drug dosage or absorption. Two other approaches for monitoring drug resistance will also be included in the database. First, genetic analysis of parasites has identified molecular markers associated
with parasite resistance to some antimalarials: CQ, SP, mefloquine, amodiaquine [12] and, possibly, lumefantrine [13–16]. These markers provide a very convenient and costeffective tool for monitoring changes in the prevalence of drug-resistant parasites. An increasing prevalence of alleles of genes known to confer resistance to a drug can also provide early warning of developing resistance [17]. Equally, a decrease in ‘resistant alleles’ can be an indication of returning sensitivity when a drug is withdrawn [17]. Second, parasites can be isolated from infected patients, and the responses to drugs of those parasites can be monitored in vitro [18]. These in vitro assays allow evaluation of the susceptibility of the parasites to additional drugs not currently in use in that location. Moreover, this method allows separate assessment of parasite responses to each component of a combination drug, a particular advantage when combinations such as ACTs are of such current importance. In vitro analysis is useful because decreasing susceptibility of parasites to a drug in use is one potential early warning that resistance could be increasing in that region [19]. So far, the relationship between molecular markers and in vitro drug sensitivity on one hand, and therapeutic efficacy on the other hand, is neither linear nor completely understood. Previous reports have focused mostly on the clinical outcome of drug treatment, but the WWARN project will include 223
Update all types of information for gauging antimalarial resistance (i.e. clinical, three-day parasite clearance, in vitro data, molecular and genetic means, and pharmacological data), linking clinical and pharmacological data from an individual patient and his/her parasites, whenever possible. This approach allows far greater scope for appropriate pooling and analysis of information gathered at different times and places, comparisons that are not possible when only summaries or aggregated data from the studies are available [20]. These wider comparisons have the potential to detect subtle signs of decreasing drug efficacy, and this evidence can then be communicated to policy makers to allow strategies for containment to be devised and implemented. Integration of WWARN into current antimalarial resistance activities WHO and WWARN will have complementary roles in the collation of the information. WHO has a responsibility to assist countries in the surveillance of antimalarial drug efficacy through established relationships with the National Malaria Control Programs (NMCP) in malariaendemic countries. The WHO also supports regional networks for the co-ordination of these activities, and these networks will also have an important role [21]. WWARN will focus on the development of the database itself through collaboration with the many other organizations that collect drug– efficacy information (reviewed in Ref. [12]) and will integrate data from these organizations to provide an inclusive database. The provision of new tools can support high-quality studies and data analysis, and will aid those who do the hard work of data collection, encouraging timely sharing of the data by publication and submission to the database. Both WHO and WWARN will be involved in sharing the combined data, analyzing trends and producing the evidence needed to assess drug efficacy on a worldwide basis. The goal of this cooperative effort is to design a system that will improve the overall quality of the data collected, analyze the collated data effectively and produce analyses that are accessible, informative and useful to all those involved in antimalarial drug deployment and use. The useful life of ACTs and other drugs that are in development must be prolonged, and the data-sharing effort can certainly play an important role [22]. Acknowledgements The World Health Organization has granted the publisher permission for the reproduction of this article; ß2010. World Health Organization. Published by Elsevier Ltd. All rights reserved. The authors gratefully acknowledge the support of the Bill & Melinda Gates Foundation. P.R. is a staff member of the World Health Organization (WHO). The author alone is responsible for the views expressed in this publication and they do not necessarily represent the decisions, policy or views of the WHO.
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